Difference between revisions of "Application Tables and Guideline Data for Use of Electrical Contact Design"

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===6.1 Application Ranges for Switching Contacts===
+
==<!--6.1--> Application Ranges for Switching Contacts==
  
−
===6.1.1 Low and Medium Electrical Loads===
+
===<!--6.1.1 -->Low and Medium Electrical Loads===
−
Switching processes at low and medium electrical loads are experienced for example in relays and switches for the measuring technology, telecommunications, automotive usage, and appliances. The switching voltage ranges from μV to 400V with currents between μA and about 100A.
+
Switching processes at low and medium electrical loads are experienced for example in relays and switches for the measuring technology, telecommunications, automotive usage and appliances. The switching voltage ranges from μV to 400V with currents between μA and about 100A.
  
−
Guided by empirically developed arc-limiting graphs typical switching processes can be distinguished. As Fig. 6.1 illustrates, voltage and current
+
Main Article: [[Low and Medium Electrical Loads| Low and Medium Electrical Loads]]
−
determine if switching occurs without arcing, results in a glow discharge, short instable arcs are generated, or a fully developed electrical arc is created. The more exact current-voltage curve characte-ristics are depending on the electrical contact material used. They also depend on the contact gap and the atmosphere the switching occurs in; an ambient air atmosphere is assumed in the shown schematic example.
 
  
−
Fig. 6.1:
+
===<!--6.1.2-->High Electrical Loads===
−
Arc-limiting graphs (schematic)
+
With high electrical loads, as usually occuring in power engineering equipment, the switching phenomena are usually due to arcing. For most applications the management of the switching arc is the key problem. Depending on the device type, different requirements are dominant, which influence the selection of the contact material. Similar to those in communications engineering, issues related to the switching characteristics and current path have to be considered.
−
1. Arc-less switching
 
−
2. Short instable arcs
 
−
3. Glow discharge
 
−
4. Full electrical arcs
 
  
−
For the different requirements on the electrical contacts in various applications it is useful to differentiate across the broad spectrum of possible load conditions guided by the arc-limiting graphs between four different partial ranges which result in typical physical effects:
+
Main Article: [[High Electrical Loads| High Electrical Loads]]
  
−
*Dry Circuit Contacts
+
==<!--6.2-->Contact Materials and Design of Contact Components==
 +
The highest reliability and electrical life of electromechanical components and switching devices can only be achieved if both, the material selection and the design of the actual contact parts, are optimized. Of course, economic considerations must also be applied when selecting the most suitable contact material and its way of application as an electrical contact. In the following <xr id="tab:Material Selection and Contact Component Design"/><!--Table 6.1--> recommendations are made for selected application examples for contact materials and contact shape or configuration.
  
−
<br/>U < 80mV <br/> I < 10mA <br/>  
+
<figtable id="tab:Material Selection and Contact Component Design">
 +
<caption>'''<!--Table 6.1:-->Material Selection and Contact Component Design'''</caption>  
  
 +
{| class="twocolortable" style="text-align: left; font-size: 12px"
 +
|-
 +
!Type of Contacts or Devices
 +
!Characteristic Requirements for Contacts
 +
!Contact Material
 +
!Design Form of Contacts
 +
|-
 +
|Contacts for dry circuits
 +
|Reliable contacting at very low currents and voltages and mostly at also<br />low contact forces
 +
|AuAg alloys, (AuPt), Au
 +
|Contact rivets, welded miniature profiles (tapes), electroplated Au, sputtered Au layers
 +
|-
 +
|Switching contacts in measuring devices
 +
|Reliable switching at low voltages and currents at low contact forces
 +
|Au and Pt alloys, (AgPd alloys)
 +
|Contact rivets, welded tips, clad parts
 +
|-
 +
|Keyboard contacts
 +
|Defined contacting, close to bounce-free make, high reliability at low switching loads
 +
|Au alloys, (AgPd), Au on Ni substrate
 +
|Au plated snap discs, Au clad wires and stamped parts, hard gold electroplated contact spots on printed circuit boards
 +
|-
 +
|Rotary switches on printed circuit boards
 +
|Good frictional wear resistance, low contact résistance
 +
|Sliding track: hard gold on Ni substrate Slider: AgPd alloy, (Hard silver)
 +
|Electroplated coatings on slide tracks; clad, welded, or riveted stamping parts
 +
|-
 +
|Slip rings with high reliability
 +
|Low and consistent contact resistance at low contact forces
 +
|Brushes: Au alloys, AgPd, AgPdCu; Slip rings: Au alloys, Ag alloys (Rh); For higher currents: Ag/C brushes against Ag slip rings
 +
|Brush wires, stamped brushes; solid, clad, or electroplated slip rings, Ag/C formed parts
 +
|-
 +
|Sliding contacts in miniature motors
 +
|Very high frictional wear resistance, sure contacting even at very low contact forces
 +
|Ag and Au alloys, Pd alloys, Au multi component alloys
 +
|Brushes from flat rolled wire or stamped; collector hard gold electroplated or clad; made from miniature profile segments
 +
|-
 +
|Centrifugal controllers for small motors
 +
|Little shape changes, defined contacting at very low contact forces and high frequency of operation
 +
|Pd alloys
 +
|Contact rivets, contact screws, welded parts
 +
|-
 +
|Connectors
 +
|Low contact resistance, corrosion resistance, sufficient frictional wear resistance, good sliding capabilities
 +
|Ag and Au alloys, Pd, PdNi; For automotive and consumer electronic at low operation numbers: Sn and Sn alloys
 +
|Electroplated layers or clad, often Au flash plated, mostly with Ni substrate layer, stamped parts from hot tin dipped strip
 +
|-
 +
|Telecommunication relays
 +
|Reliable contacting even at high operational frequency
 +
|Ag, AgPd, Au alloys, PdRu
 +
|Rivets, welded profile segments
 +
|-
 +
|Reed relay contacts
 +
|High reliability at low currents independent of atmospheric environment
 +
|Au, (Rh)
 +
|Switch paddles FeNi with partially diffused Au, (electroplated Rh)
 +
|-
 +
|Relays in electronic circuits
 +
|High reliability at low switching loads and compact device design
 +
|Au alloys, AgPd, Ag alloys
 +
|Stamped springs from seam-welded profiles, welded miniature profile (tape) segments, contact rivets
 +
|-
 +
|GP relais (Elementary relays)
 +
|Low arc erosion, high weld resistance, low and consistent contact resistance
 +
|Ag/Ni, Ag/SnO<sub>2</sub>, (Ag/CdO), Ag/ZnO,AgNi0.15, (Ag)
 +
|Solid and composite contact rivets, welded miniature profile (tape) segments
 +
|-
 +
|Automotive relays
 +
|Low material transfer, low contact resistance, high weld resistance
 +
|AgNi0.15, Ag/SnO<sub>2</sub>, Ag/Ni
 +
|Contact rivets, welded miniature profile (tape) segments
 +
|-
 +
|Flasher relays (automotive, > 3 Mio operations)
 +
|Low material transfer, high arc erosion resistance, low contact resistance
 +
|PdCu15 and 40 (Anode) vs. AgNi0.15, AgCu3 (Cathode), Ag/ZnO, Ag/SnO<sub>2</sub>
 +
|Contact rivets, welded miniature profile (tape) and strip segments
 +
|-
 +
|Breaker points (automotive ignition)
 +
|Very high arc erosion resistance, high switching frequency
 +
|W
 +
|Tips or discs welded to formed parts or Fe supports
 +
|-
 +
|Automotive horn contacts
 +
|High arc erosion resistance at extremely high number of switching operations
 +
|W, Ag/SnO<sub>2</sub>
 +
|Contact rivets, W weld buttons, springs or formed parts with brazed or welded tips
 +
|-
 +
|Appliance switches
 +
|Low contact resistance, reasonable arc erosion and weld resistance
 +
|AgNi0.15, Ag/Ni, Ag/SnO<sub>2</sub>, (Ag/CdO)
 +
|Contact rivets, welded contact parts
 +
|-
 +
|Temperature controllers (Thermostats)
 +
|Defined contacting point even at slow motion make, high operating temperatures
 +
|AgNi0.15, Ag/Ni, Ag/SnO<sub>2</sub>, (Ag/CdO)
 +
|Contact rivets, welded contact parts, weld buttons
 +
|-
 +
|Wiring devices (Light switches)
 +
|Low contact resistance, reasonable arc erosion and weld resistance
 +
|AgNi0.15, AgCu, Ag/Ni, with make peaks also Ag/ZnO, (Ag/CdO)
 +
|Contact rivets, welded contact parts
 +
|}
 +
</figtable>
  
−
*Low Level (Load) Contacts
 
  
−
U = 80 to 300mV
+
Table 1: '''Material Selection and Contact Component Design (Fortsetzung)'''
−
I < 10mA
 
  
−
*Intermediate Level (Load) Contacts
+
{| class="twocolortable" style="text-align: left; font-size: 12px"
 +
|-
 +
!Type of Contacts or Devices
 +
!Characteristic Requirements for Contacts
 +
!Contact Material
 +
!Design Form of Contacts
 +
|-
 +
|Automatic staircase lighting switches
 +
|High arc erosion and weld resistance
 +
|Ag/Ni, Ag/SnO<sub>2</sub>, (Ag/CdO), Ag/C against Ag/SnO<sub>2</sub>
 +
|Rivets, welded contact parts
 +
|-
 +
|Miniature Circuit breakers
 +
|Extremely high weld resistance, low temperature rise in use, sufficient arc erosion resistance
 +
|I< 50 A: Ag/C97/3 (Cu/C) against Cu, I> 50 A : Ag/C97/3 o. 95/5 against AgCu3, Ag/Ni90/10 o. 80/20, Ag/W, Ag/WC (USA)
 +
|Welded contact parts (Ag/C), clad stamped parts
 +
|-
 +
|Fault current circuit breakers
 +
|Extremely high weld resistance, low contact resistance, high arc erosion resistance
 +
|Stationary contact: Ag/C96/4 o. 95/5 Movable contact: Ag/Ni, Ag/MeO, Ag/W, Ag/WC, Ag/WC/C
 +
|Welded and brazed contact parts
 +
|-
 +
|Micro snap switches
 +
|Low contact resistance, no sticking during make operation
 +
|AgNi 0,15, Ag/Ni, Ag/SnO<sub>2</sub>, (Ag/CdO)
 +
|Rivets, clad or welded contact parts
 +
|-
 +
|Control and auxiliary switches
 +
|Low contact resistance over extended life span
 +
|Ag, AgNi 0,15, AgCu, Ag/Ni
 +
|Rivets, clad stamped parts, (gold plated rivets), welded contact parts
 +
|-
 +
|Auxiliary and control relays
 +
|High reliability over extended life span, low contact resistance
 +
|AgNi 0,15, Ag/Ni
 +
|Rivets, clad profile parts, welded contact parts
 +
|-
 +
|Cam switches (higher loads)
 +
|High arc erosion and weld resistance, low contact resistance
 +
|AgCu, Ag/Ni, Ag/SnO<sub>2</sub>, Ag/ZnO, (Ag/CdO)
 +
|Rivets, welded contact parts
 +
|-
 +
|Contactors
 +
|High arc erosion and weld resistance, low contact resistance
 +
|I< 20A : Ag/Ni, Ag/SnO<sub>2</sub> I>20A : Ag/SnO<sub>2</sub>, (AgCdO)
 +
|Welded and brazed contact tips
 +
|-
 +
|Motor -protective circuit breakers
 +
|Extremely high weld resistance, low contact resistance
 +
|Ag/ZnO, Ag/C against Ag/Ni
 +
|Welded contact parts, toplay stamping parts
 +
|-
 +
|Power switches and circuit breakers
 +
|Extremely high arc erosion and weld resistance, low contact resistance
 +
|Ag/ZnO, Ag/SnO<sub>2</sub> , Ag/C against Ag/Ni o. Ag/W, Ag/W, Ag/WC/C, Ag/W against Ag/CdO
 +
|Brazed and welded contact tips and formed parts
 +
|-
 +
|Power switches with arcing and main contacts
 +
|High weld resistance, low contact resistance, high arc erosion resistance
 +
|Arcing contacts: W/Ag, W/Cu, (Cu) Main contacts: Ag/Ni, Ag/ZnO, Ag/W, Ag/WC
 +
|Brazed and welded contact tips and formed parts
 +
|-
 +
|Disconnect switches
 +
|Low contact resistance, sufficient mechanical strength
 +
|AgNi 0,15, Ag/Ni, Ag (electroplated)
 +
|Electroplated coatings, brazed contact parts
 +
|-
 +
|High voltage circuit breakers
 +
|Arcing contacts: highest arc erosion resistance Main contacts: low contact resistance
 +
|Arcing contacts: W/Cu-infiltrated Main contact CuCrZr silver plated,
 +
|Cast-on, electron-beam welded (or brazed) formed parts, percussion welded pins
 +
|-
 +
|Load disconnect switches (medium and high voltage)
 +
|Low contact resistance, sufficient mechanical strength, high arc erosion resistance of precontacts
 +
|Arcing contact: W/Cu, Cu, Ag/C Main contact: Cu, CuCrZr silver plated, Ag/Ni, AgNi0,15, Ag/C
 +
|Arcing contacts: brazed or welded parts Main contacts: silver plated, brazed or welded parts
 +
|-
 +
|Vacuum contactors
 +
|Low chopping current, high arc erosion resistance, low contact resistance
 +
|Low gas content W/Cu, W/CuSb, WC/Ag, CuCr
 +
|Contact discs, shaped rings
 +
|-
 +
|Vacuum circuit breakers
 +
|High switching capacity, low contact resistance
 +
|Low gas content CuCr
 +
|Contact discs
 +
|-
 +
|Transformer tab changers
 +
|High arc erosion resistance in oil environment
 +
|W/Cu in filtrated with approx. 70%
 +
|Brazed contact tips
 +
|-
 +
|Disconnect switches in high voltage circuits
 +
|Low contact resistance, low mechanical wear, sufficient arc erosion resistance during current commutation
 +
|Ag (electroplated), AgNi0,15, Ag/SnO<sub>2</sub>
 +
|Electroplated coatings, brazed parts, Toplay profile segments
 +
|}
 +
'''Notes:'''
 +
<xr id="tab:Material Selection and Contact Component Design"/><!--Table 6.1--> is meant to give suggestions for the use of contact materials for the specified devices. For most of the contact materials, we deliberately did not indicate the exact composition and, as for Ag/SnO<sub>2</sub> and AgZnO, did also not include specific additives. The final material composition depends on specific design parameters of the electrical device. Advise on the special properties of specific contact materials can be found in chapter 2 [[Contact Materials for Electrical Engineering| Contact Materials for Electrical Engineering ]].
  
−
U = 300mV – 10V
+
==<!--6.3-->Design Technologies for Contacts==
−
I = 10mA – 100mA
+
A multitude of technologies is available and used for the actual manufacturing of contact components (see chapter 3 [[Manufacturing Technologies for Contact Parts|Manufacturing Technologies for Contact Parts]]). The desired contact shape however, requires specific material properties like formability and weldability, which cannot be fulfilled by all materials in the same way. In addition, the design of the contact part must be compatible with the stresses and requirements of each switching device. The following <xr id="tab:Design Technologies for Contacts"/><!--table 6.2--> combines contact design, contact material and specific applications.
  
−
*Low Power (Load) Contacts
 
  
−
U > 10V
+
<figtable id="tab:Design Technologies for Contacts">
−
I > 300mA
+
<caption>'''<!--Table 6.2:-->Design Technologies for Contacts'''</caption>
  
−
*Dry Circuit Contacts
+
{| class="twocolortable" style="text-align: left; font-size: 12px"
−
This load range is characterized by the fact that the voltage is below the
+
|-
−
softening voltage of the respective contact material (< approx. 80mV) and the
+
!Contact Parts, Semi-finished Materials
−
current stays below 10mA. Because of this low electrical load the switching
+
!Typical Contact Materials and Dimensions
−
occurs without any electrical discharge and also without any significant thermal
+
!Main Areas of Application
−
stress on the contact spot. The main influences on the contact behavior are
+
!Remarks
−
therefore chemical and mechanical in nature, such as contamination, and dust
+
|-
−
or abrasion particles for-med on the contact surfaces. The required high
+
|Contact rivets solid, inserted wire segments
−
reliability can only be reached by using highly corrosion resistant contact
+
|Ag, Ag alloys, Au alloys, Pd alloys, Ag/Ni, Ag/C97/3, Ag/MeO (1.2 – 8 mm Ø)
−
materials. Since dust particle contamina-tions play a major role in determining
+
|All types of switches in the communications, automotive or power distribution technology simple contact component, universally applied, selection through economic aspects
−
the failure rate of these contacts, double (bifurcated) or multiple contacts are
+
|Secure rivet attachment only with sufficiently thick shank (shank Ø = 1⁄2 head Ø); change-over contacts by forming secondary head from longer shanks
−
used frequently.
+
|-
 +
|Contact rivets, clad (Composite Rivets)
 +
|Ag, Ag alloys, Ag/Ni, Ag/MeO on Cu base (2 ~ 10 mm Ø)
 +
|All types of switches in the communications, automotive or power engineering
 +
|Secure rivet attachment only with sufficiently thick shank (shank Ø = 1⁄2 head Ø)
 +
|-
 +
|Contact rivets with brazed surface layer
 +
|Tungsten and difficult to form powder metallurgical materials (i.e. Ag/C) on Cu or Fe bases (1 ~ 12 mm Ø)
 +
|Switches for power engineering, W layers mostly for controls
 +
|Tungsten contact to be staked (riveted) with moderate force or using orbital riveting; for Fe bases also warm-forming
 +
|-
 +
|Contact screws
 +
|Any contact material on Fe and CuZn screws, brazed, (1 ~ 10 mm Ø, M 2 ~ M 10)
 +
|Adjustable contacts for controls and horns
 +
|During brazing carrier may get soft
 +
|-
 +
|Vertically welded wire segments
 +
|Ag, Ag alloys, Ag/Ni, AgPd, Au alloys (wire 0.6 ~ 5 mm Ø)
 +
|Contact parts for control functions and power engineering; economical manufacturing at higher quantities
 +
|Welding and subsequently heading or orbital forming of head shape
 +
|-
 +
|Horizontally welded wire and profile segments
 +
|Au alloys, Pd alloys, Ag, Ag alloys, Ag/Ni, Ag/MeO, Ag/C in strip or profile form, Miniature profiles - also multi-layered (profile width 0.2 ~ 5 mm)
 +
|Contact parts for communication, measurement, controls and power engineering; very economical with respect to precious metal usage
 +
|Welding synchronized to stamping / forming on special equipment
 +
|-
 +
|Weld buttons
 +
|Ag, Ag alloys, Ag/Ni, Ag/MeO on Steel, Ni, Monel; Ag/W, Ag/Mo (1.5 ~ 10 mm Ø)
 +
|Welded for example to steel springs or thermostatic bimetals for temperature controls
 +
|Metallurgical bond through simple projection welding remains strong in temperature cycling applications
 +
|-
 +
|Tungsten weld buttons
 +
|W on Ni or Ni-plated Fe, (2 ~ 6 mm) with weld projections
 +
|Contacts for controls, ignition points and horns; arcing contacts in special relays
 +
|For change-over contact welded on both sides of carrier
 +
|-
 +
|Brazed contact tips
 +
|All materials and dimensions, oxide and graphite containing materials with brazable backing, carrier parts from Fe, Cu and Cu alloys, at higher strength requirements also CuCrZr or CuBe
 +
|Medium and higher load switching devices for power engineering
 +
|Braze alloy layer with low meting point, carriers may soften during brazing
 +
|-
 +
|Clad contact materials (Contact Bimetals), totally covered or with inlayed strips
 +
|Ductile precious metals on Cu and Cu alloys, minimum precious metal layer 2% of total strip thickness for Ag and Ag alloys, 0.5% of total strip thickness for Au alloys (with Ni intermediate layer), max. inlayed thickness 50% of total, strip width starting at 2 mm
 +
|Clad contact springs; stamped and formed parts for communications and power engineering; aluminum clad for bonding capability
 +
|Metallurgical bond; inlayed strip stamped perpendicular or at angle to strip direction; avoid bends at the cladding edges
 +
|-
 +
|Strips or profiles with brazed contact material layers (Toplay material)
 +
|Ag, Ag alloys, Ag/Ni, Ag/MeO on Cu and Cu alloy carriers, total width 10 ~ 100mm, carrier thickness 0.3 – 5 mm, Ag strip cross section from 0.3 x 3 mm<sup>2</sup>, strip thickn. to be &le; carrier thickn.
 +
|Stationary and moving contact bridges for power engineering switching devices
 +
|Contact layers brazed with Ag brazing alloys; strips re-hardened during profile rolling
 +
|-
 +
|Seam-welded contact strips or profiles
 +
|Wire, strip, miniature profiles (solid or clad) welded to Cu alloy carrier strip (0.3 – 3 mm Ø or up to 5 mm width)
 +
|Switches, pushbuttons, relays, auxiliary contactors, sliding contacts
 +
|Broad usability, highly economical, thin spring hard carriers can be used
 +
|-
 +
|Miniature profiles (Weld tapes)
 +
|Mostly high precious contact materials, double or multi layer, Ni, Monel, or Cu alloy carrier; miniature-profile width 0.2 – 2 mm
 +
|Welded profile segments for contact parts in communication, measurement and control engineering
 +
|Manufacturing of cross-directional contact spots; most economical precious metal usage
 +
|}
  
−
*Low Level Contacts
 
−
In this load range the voltage is between the softening and melting voltage of the
 
−
contact material and the current is below 10mA. Because of the higher voltage
 
−
compared to dry circuits a temperature induced softening of the contacting
 
−
surface area occurs which increases the contacting area. Besides high
 
−
corrosion resistance a higher hardness of the contact materials is required for
 
−
this load range.
 
  
−
*Intermediate Level Contacts
+
Table 2: '''Design Technologies for Contacts (Fortsetzung)'''
−
This load range is characterized by a voltage below the minimum arc voltage
 
−
and a current below 300mA. In this range discharges occur between the
 
−
contacts which can electrically or thermally destroy at least partially
 
−
contamination layers on the contact surfaces. At lower electrical load organic
 
−
films may not be thermally destroyed completely which may lead to a steep
 
−
increase in contact resistance. In DC circuits short arcs may result in material
 
−
transfer. Contact materials for this load range need to be resistant against
 
−
corrosion and the tendency to material transfer.
 
  
−
*Low Power (Load) Contacts
+
{| class="twocolortable" style="text-align: left; font-size: 12px"
−
The main characteristic of this load range is the presence of stable electrical
+
|-
−
arcs. Caused by the interaction between contact material and electrical arcs the
+
!Contact Parts, Semi-finished Materials
−
electrical life of contacts is limited by arc erosion or material transfer and in the
+
!Typical Contact Materials and Dimensions
−
case of higher make currents also by weld failures. For contact material
+
!Main Areas of Application
−
selection the type of electrical load, i.e. resistive, inductive, capacitive, motor
+
!Remarks
−
load, which determine the time function of the electrical current, is most critical.
+
|-
 +
|Clad profiles
 +
|Ag, Ag alloys, Ag/Ni, Ag/MeO, on Cu or Cu alloy carriers, all cross-sectional areas that can be drawn or rolled; Profile width: 2 ~ 10 mm
 +
|Profile segments as contact areas for low and high voltage switching devices
 +
|More complex shapes require costly tooling
 +
|-
 +
|Sintered and infiltrated parts
 +
|W-, WC-, Mo-based materials, in almost any contact shapes
 +
|Contact parts for low and high voltage switching devices
 +
|Single parts pressing; mostly with weld projec- tions and braze alloy coating on underside
 +
|-
 +
|Formed arc erosion parts
 +
|W/Cu infiltration materials, parts in almost any shapes
 +
|Arcing contacts for extreme duty switching devices, i.e. SF<sub>6</sub> circuit breakers
 +
|Attachment to Cu carriers by cast-on, percussion welding, electron-beam welding; rarely by brazing
 +
|-
 +
|Low gas content contact parts
 +
|W/Cu-, WC/Ag-, CuCr-based materials, rings and discs in almost any shape
 +
|Shaped contact parts for vacuum switches (contactors, power switches, circuit breakers)
 +
|Brazing to Cu carriers requires special brazing alloys
 +
|-
 +
|Cast-on contact parts
 +
|W/Cu cast on with Cu, shaped parts and rings up to 100 mm Ø
 +
|Arcing contacts in high voltage switchgear
 +
|Seamless bond interface, carriers get hardened through subsequent forming
 +
|-
 +
|Electron-beam welded contact parts
 +
|W/Cu on Cu or CuCrZr contact rods, tubes, tulips
 +
|Arcing contacts in high voltage circuit breakers
 +
|Seamless bond interface, withstands high mechanical and thermal stresses
 +
|-
 +
|Silver electroplating
 +
|Layer thickness up to 20 μm, mostly on Cu and Cu alloys
 +
|Connecting areas and no-load switching contacts in power engineering; rotary switches, sliding contacts, connectors
 +
|For switching contacts only under very low loads
 +
|-
 +
|Gold electroplating
 +
|Flash plating 0.1 – 0.2 μm on Ag alloys, and Cu alloys; contact layers 0.5 – 5 μm mostly with intermediate Ni layer
 +
|Contacts with low current and voltage loads, connectors, rotary and sliding switches, contact areas on printed circuit boards
 +
|Flash plating only limited effective as corrosion resistant layer on silver contacts
 +
|-
 +
|Selectively electroplated strips
 +
|Stripe coatings: Tin plating 1- 10 μm, Ag plating 1 – 20 μm, Au plating 0.2 – 5 μm; stripe width 2 mm min, stripe distance > 2 mm; carrier material: Cu and Cu alloys, Ni alloys, stainless steel; strip thickness: 0.1 ~ 1 mm; strip width: 5 ~ 100 mm
 +
|Contact parts for connectors, keyboard switches, rotary and sliding switches; bondable areas (Au) for electronic components
 +
|Economic manufacturing for partially plated parts; hard gold with Ni intermediate layer possible but has limited formability
 +
|-
 +
|Selectively electroplated pre-stamped strips, Spot gold plating
 +
|Continuous partial electroplating of pre-stamped and coined contact spots; all
 +
precious metals; intermediate layers of Cu or Ni; selective tinning of connector contact areas and terminal ends; carrier materials up to 1 mm thick, strip width up to ~ 80 mm
 +
|Precious metal plating of switching contacts, connector parts, and terminal pins in the communication technology
 +
|Crack-free and wear resistant layers possible since contact areas are already formed to final shape
 +
|-
 +
|Sputtered profiles
 +
|Au, Au alloys in any composition; layer thickness 0.1 – 5 μm
 +
|Contact profiles for relays, switches and keyboard contacts in the information and measuring technology
 +
|High purity contact layers for high reliability
 +
|-
 +
|Hot-dip tinned strips
 +
|All around or stripe tinning 1 ~ 15 μm
 +
|Connectors for automotive and consumer technology; screw and crimp connectors
 +
|Economic coating method; does not form (Sn) whiskers
 +
|}
 +
</figtable>
  
−
Fig. 6.2 gives an overview for commonly used electrical contact materials for
+
==<!--6.4-->Formulas and Design Rules==
−
different load ranges in switches used in the information technology up to the
 
−
transition range towards power switching applications. The ranges are
 
−
illustrated as a function of switching current and voltage.
 
  
−
Fig. 6.2:
+
===<!--6.4.1-->Definition of Terms and Symbols===
−
Application ranges (switching current
 
−
and voltage) of contact materials for
 
−
information technology and
 
−
transitioning into the power switching
 
−
devices
 
−
 
 
−
For lower electrical loads mainly high precious materials based on Au and Pt are
 
−
used because of their high corrosion resistance, the latter materials however
 
−
used only in limited quantities because of the high price of platinum metals. Ag
 
−
based materials cover the medium load range and are alloyed with Pd for
 
−
currents <1A and voltages > 24V, and for loads above these levels Ag
 
−
composite materials with additions of Ni, or the metal oxides SnO<sub>2</sub>, ZnO, or CdO
 
−
are used. While the Pd addition reduces the silver sulfide formation in sulfur
 
−
containing environments, adding metal oxides increases the resistance against
 
−
welding and arc erosion at higher make currents. At high switching currents and
 
−
switching frequency tungsten containing contacts are used, mainly as switching
 
−
pre-contacts which absorb the electrical arcs at high make and break currents
 
−
while parallel contacts mainly produced from silver containing materials such as
 
−
AgNi0.15 (Fine-Grain Silver) are employed for current carrying in the closed
 
−
condition.
 
−
 
 
−
Primarily the specific stresses on the contact assemblies must be considered
 
−
during the selection of contact materials:
 
−
 
 
−
*During make of bouncing contacts mechanical wear, arc erosion,
 
−
and material transfer occur, the latter mostly in DC switching circuits.
 
−
 
 
−
*In the closed condition the value and consistency of the contact
 
−
resistance must be considered. Both are affected by the resistance to
 
−
corrosion and changes in composition caused by the effects of arcing.
 
−
 
 
−
*During off-switching (break) the frictional wear leads to material loss;
 
−
besides this material transfer and arc erosion effect contact life.
 
−
 
 
−
===6.1.2 High Electrical Loads===
 
−
At high electric loads that usually occur in power engineering devices the
 
−
switching phenomena are mostly related to arc formation. For most applications
 
−
the management of the switching arc is the key problem. Depending on the
 
−
device type different require-ments are dominant which influence the selection
 
−
of the contact material. Similar to those in communications engineering, issues
 
−
related to the switching characteristics and current path have to be considered.
 
−
 
 
−
*Make operation
 
−
Make erosion caused by pre-close and bounce arcs
 
−
Welding mainly during bounce arc
 
−
Mechanical wear mainly through bounce and relative motion
 
−
 
 
−
*Current carrying through closed contacts
 
−
Increased contact resistance and temperature rise during
 
−
nominal load
 
−
Welding through high contact resistance during overload and
 
−
short circuit load
 
−
Welding during dynamic separation of the contacts with arcing
 
−
 
 
−
*Break operation
 
−
Arc erosion during opening
 
−
Arc movement
 
−
Arc extinguishing
 
−
Mechanical wear
 
−
 
 
−
als bilder?
 
−
 
 
−
The typical application ranges for different contact materials in devices for
 
−
power engineering are illustrated in Figs. 6.3 and 6.4. In the lower load ranges
 
−
mostly silver and fine grain silver (AgNi0.15) are used because of their high
 
−
electrical and thermal conductivity. With increasing currents the more arc
 
−
erosion resistant AgCu alloy materials are used. For the medium current range
 
−
up to 100A Ag/Ni composite materials are advantageous because of their lower
 
−
and consistent contact resistance and their favorable re-solidification
 
−
properties. If higher welding and at the same time arc erosion resistance are
 
−
required, such as for example in motor contactors for switching currents up to
 
−
5,000A, silver – metal oxide materials are superior. In protective switches
 
−
(mainly circuit breakers) which are required to handle high short circuit energies,
 
−
asymmetrical contact pairings are used where the fixed contact is made from
 
−
Ag/C materials and the moving ones consist, depending on the device
 
−
characteristics, of Cu, Ag/Ni, or Ag/W. For UL rated and certified circuit
 
−
breakers (UL = Underwriters Laboratories) which are mainly used in North
 
−
American power distribution networks symmetrical pairings of Ag/W or Ag/WC
 
−
are the preferred contact materials.
 
−
 
 
−
For very high loads in main power switches and power circuit breakers for
 
−
medium and high voltage power engineering applications the most suitable
 
−
materials are tungsten based infiltration materials such as W/Cu.
 
−
 
 
−
Fig. 6.3:
 
−
Typical application ranges
 
−
for contact materials in
 
−
power engineering
 
−
switching devices as a
 
−
function of switching
 
−
current and voltage
 
−
 
 
−
Fig. 6.4:
 
−
Application ranges for
 
−
contact materials in power
 
−
engineering switching
 
−
devices as a function of
 
−
switching current and
 
−
numbers of operation
 
−
 
 
−
 
 
−
===6.2 Contact Materials and Design of Contact Components===
 
−
The highest reliability and electrical life of electromechanical components and
 
−
switching devices can only be achieved if both, the material selection and the
 
−
design of the actual contact parts, are optimized. Economic considerations
 
−
must of course also be applied when selecting the most suitable contact
 
−
material and its way of application as an electrical contact. In the following Table
 
−
6.1 recommendations are made for selected application examples for contact
 
−
materials and contact shape or configuration.
 
−
 
 
−
Table 6.1: Material Selection and Contact Component Design
 
−
 
 
−
Table 6.1: Material Selection and Contact Component Design
 
−
 
 
−
 
 
−
===Notes:===
 
−
Table 6.1 is meant to give suggestions for the use of contact materials for the
 
−
specified devices. For most of the contact materials we deliberately did not
 
−
indicate the exact composition and, as for Ag/SnO<sub>2</sub> and AgZnO, did also not
 
−
include specific additives. The final material composition depends on specific
 
−
design parameters of the electrical device. Advise on the special properties of
 
−
specific contact materials can be found in chapter 2.
 
−
 
 
−
===6.3 Design Technologies for Contacts===
 
−
A multitude of technologies is available and used for the actual manufacturing of
 
−
contact components (see chapter 3). The desired contact shape however
 
−
requires specific material properties like for example formability and weldability
 
−
which cannot be fulfilled by all materials in the same way. In addition the design
 
−
of the contact part must be compatible with the stresses and requirements of
 
−
each switching device. The following table 6.2 combines contact design,
 
−
contact material, and specific applications.
 
−
 
 
−
 
 
−
 
 
−
Manufacturing of Conductive Preparations
 
−
bild
 
−
 
 
−
Table 6.2: Design Technologies for Contacts
 
−
 
 
−
Table 6.2: Design Technologies for Contacts
 
−
 
 
−
 
 
−
===6.4 Formulas and Design Rules===
 
−
 
 
−
===6.4.1 Definition of Terms and Symbols===
 
 
Note: The symbols for electrical contact specific terms (i.e. contact area,
 
Note: The symbols for electrical contact specific terms (i.e. contact area,
 
contact resistance, etc. have been retained from the german version of the Data
 
contact resistance, etc. have been retained from the german version of the Data
Line 232: Line 386:
 
used here from german R<sub>k</sub>, in english mostly R<sub>c</sub>.
 
used here from german R<sub>k</sub>, in english mostly R<sub>c</sub>.
  
−
*'''Electrical contact''' is a property which is generated through the touching of
+
Main Article: [[Definition of Terms and Symbols| Definition of Terms and Symbols]]
−
two electrically conducting surfaces.
 
−
 
 
−
*'''Contact part''' is a metallic component which is designed to create or interrupt
 
−
an electrical contact (is frequently replaced by the term “contact” if it is clearly
 
−
understandable that a physical piece or item is meant).
 
−
 
 
−
*'''Contact area''' is the whole area on a contact part that may be used for
 
−
contacting.
 
−
 
 
−
*'''Apparent contact area A<sub>s</sub>''' is the part of the contact area on contact parts that
 
−
can make physical contact during the touching of two contacts.
 
−
 
 
−
*'''Load bearing contact area A<sub>t</sub>''' is the part of the apparent contact area which
 
−
is affected by the contact force. It is the sum of all microscopic actual touching
 
−
points.
 
−
 
 
−
*'''Effective contact area A<sub>w</sub>''' is the part of the load bearing contact area through
 
−
which current is flowing and therefore the sum of all current carrying touching
 
−
areas (a-spots), A<sub>w</sub>< A<sub>t</sub>< A<sub>s</sub>.
 
−
 
 
−
*'''Contour area A<sub>n</sub>''' is the contiguous area which includes all effective
 
−
a-spots, A<sub>w</sub>< A<sub>n</sub>< A<sub>s</sub>; A<sub>n</sub>≠ A<sub>t</sub>.
 
−
 
 
−
*'''Contact resistance R<sub>k</sub>''' is composed of the constriction resistance and the film
 
−
resistance.
 
−
 
 
−
*'''Constriction resistance R<sub>e</sub>''' is the incremental electrical resistance generated
 
−
by the constriction of the currents paths in the touching area
 
−
(a-spot).
 
−
 
 
−
*'''Film resistance R<sub>f</sub>''' is generated by a foreign matter layer, which for ex. is
 
−
formed by a reaction of the contact material surface with the surrounding
 
−
atmosphere (a surface film is a substance on the contact surface with
 
−
different properties than those of the actual contact material).
 
−
 
 
−
*'''Path resistance R<sub>d</sub>''' is the total electrical resistance between reference
 
−
points (usually the device terminals) which can be freely chosen but must
 
−
be defined. It is the sum of the conductor resistance R<sub>b</sub> and the contact resistance R<sub>k</sub>.
 
−
 
 
−
*'''Contact force F<sub>k</sub>''' is the force that is exerted between the two contact
 
−
parts in the closed position.
 
−
 
 
−
*'''Frictional wear''' is the loss of material caused by mechanical wear
 
−
between contact parts.
 
−
 
 
−
*'''Bounce''' is the single or multiple interruption of conduction between
 
−
contact parts during the make operation caused by alternating
 
−
transformation of kinetic to potential energy.
 
−
 
 
−
*'''Contact wear''' includes all changes on a contact surface. Mechanical
 
−
and electrical wear must be distinguished.
 
−
 
 
−
*'''Material transfer''' is the transfer of contact material from one contact
 
−
part to the other. It occurs mainly during switching of DC loads. The
 
−
direction of the transfer depends on the load circuit properties and the
 
−
contact materials used.
 
−
 
 
−
*'''Arc erosion''' is the loss of material into the surrounding of the contact
 
−
spot which is generated by electrical arcing. It occurs during contact make
 
−
as well as break operations.
 
−
 
 
−
*'''Contact welding''' occurs when melt-liquefied touching areas of the
 
−
contact parts come in contact with each other. The melting occurs during
 
−
high current carrying through these areas. During make operations this
 
−
occurs through bounce arcs, on closed contacts a too high contact
 
−
resistance or dynamic separation of the contacts due to high short circuit
 
−
currents can cause the welding of the contacts. The welding then may
 
−
cause a device failure if the device specific opening forces cannot break
 
−
the weld connection.
 
−
 
 
−
*'''Arc movement''' happens when during the break operation a sufficiently high
 
−
magnetic field is generated which exerts a force on the electrical arc which is
 
−
then moved from the originating spot towards an arc chute (or arc splitting
 
−
plates).
 
−
 
 
−
*'''Arc extinguishing''' means the process of letting the current go to zero and
 
−
transferring the arcing gap from a conducting to the non-conducting stage.
 
−
Selecting the most effective extinguishing measures depend mostly on the
 
−
current characteristics, the current value and the circuit voltage.
 
−
 
 
−
*'''Recovery''' of an arc gap during contact opening is defined as the process of
 
−
the electrically conducting plasma of an arc losing its electrical conductivity after
 
−
reaching current-zero.
 
−
 
 
−
*'''Symbole used'''
 
−
 
 
−
bild
 
−
 
 
−
 
 
−
===6.4.2 Contact Physics – Formulas===
 
−
 
 
−
*'''Constriction resistance'''
 
−
 
 
−
Re = D/2a
 
−
(Single spot contact according to Holm; circular touching spot between clean
 
−
contact surfaces)
 
−
Re = D/2Na
 
−
(Multi-spot contact according to Holm without influence between the N
 
−
individual spots)
 
−
Re = D/2 x E ai + 3B D/32N² x E E (sij) i = j
 
−
(Multi-spot contact according to Greenwood considering the influence between
 
−
the spots)
 
−
 
 
−
als bild?
 
−
 
 
−
 
 
−
*'''Contact resistance'''
 
−
RK = Re + Rf
 
−
 
 
−
*'''Path resistance'''
 
−
Rd = Rb + RK
 
−
 
 
−
*'''Contact resistance and contact force'''
 
−
R = 280D ³ E(F · r) K K
 
−
(According to Holm model for film-free spherical contact surfaces with plastic
 
−
deformation of the contact material; F < 1 N for typical contact materials) k
 
−
RK = 9000 D H/ FK
 
−
(According to Holm model for film-free spherical contact surfaces with plastic
 
−
deformation of the contact material; F > 5 N for typical contact materials)
 
−
 
 
−
 
 
−
*'''Dynamic contact separation''' (without considering magnetic fields caused by the current path)
 
−
 
 
−
FA 0,8 x I²
 
−
(Rule of thumb with F in N and I in kA)
 
  
−
*'''Contact voltage and max. contact temperature'''
+
===<!--6.4.2-->Contact Physics – Formulas===
−
T kmax 3200 UK
 
  
−
*'''Contact resistance at higher contact forces (according to Babikow)'''
+
Main Article: [[Contact Physics – Formulas| Contact Physics – Formulas]]
−
R = cF -m K K
 
−
For F between 10 and 200 N K
 
−
c = material dependent proportionality factor
 
−
m = shape dependent exponent of the contact force
 
  
 +
===<!--6.4.3-->Closed Contacts===
  
−
===6.4.3 Closed Contacts===
+
<div class="multiple-images">
  
−
Fig. 6.5: Rough flat surface. a) before and b) during making contact with an ideally
+
<figure id="fig:Rough flat surface">
 +
[[File:Rough flat surface.jpg|left|thumb|Figure1: Rough flat surface. a) before and b) during making contact with an ideally
 
smooth flat surface; c) Schematic of the apparent, load bearing and effective
 
smooth flat surface; c) Schematic of the apparent, load bearing and effective
−
contact areas (not to scale; dashed lines are elevation lines)
+
contact areas (not to scale; dashed lines are elevation lines)]]
−
 
+
</figure>
−
Fig. 6.6:
 
−
Contact resistance of crossed rods
 
−
as a function of the contact force for gold, silver
 
−
and silver-palladium alloys
 
  
−
Table 6.3: Thermo-electrical Voltage of Contact Materials (against Copper)
+
<figure id="fig:Contact-resistance-of-crossed-rods">
 +
[[File:Contact-resistance-of-crossed-rods.jpg|right|thumb|Figure 2: Contact resistance of crossed rods as a function of the contact force for gold, silver and silver-palladium alloys]]
 +
</figure>
 +
</div>
 +
<div class="clear"></div>
  
  
−
===6.4.4 Switching Contacts===
+
<figtable id="tab:Thermo-electrical Voltage of Contact Materials (against Copper)">
 +
<caption>'''<!--Table 6.3:-->Thermo-electrical Voltage of Contact Materials (against Copper)'''</caption>
  
−
*'''Effects during switching operations'''
+
{| class="twocolortable" style="text-align: left; font-size: 12px"
 +
|-
 +
!
 +
!Contact Materials
 +
!Thermo-electric Voltage (0 - 100°C) [mV]
 +
|-
 +
|Pure metals
 +
|Ag<br />Au<br />Pt<br />Ir<br />Pd<br />Rh<br />Re<br />Cu<br />W<br />Mo
 +
| + 0.04<br />+ 0.06<br />+ 0.78<br />+ 0.13<br />+ 1.35<br />+ 0.08<br />+ 0.78<br />0<br />- 0.46<br />- 0.73
 +
|-
 +
|Alloys/Composite materials
 +
|AgCu 3<br />AgPd 30<br />AgPd 40<br />AgPd 50<br />AgPd 60<br />Ag/Ni 10<br />Ag/Ni 20<br />Ag/W 65<br />AuNi 5<br />AuAg 20<br />AuPt 10<br />PtW 5<br />Ptlr 10<br />Ptlr 20<br />PtRu 5<br />PtRu 10<br />PdCu 15<br />PdCu 40
 +
| + 0.026<br />+ 0.125<br />+ 0.198<br />+ 0.321<br />+ 0.412<br />+ 0.23<br />+ 0.27<br />+ 0.01<br />+ 4.7<br />+ 2.76<br />+ 1.11<br />+ 0.67<br />+ 0.56<br />+ 0.60<br />+ 0.32<br />+ 0.13<br />+ 0.180<br />+ 0.247
 +
|}
 +
</figtable>
  
−
Fig. 6.7 Contact opening with arc formation (schematic)
+
===<!--6.4.4-->Switching Contacts===
  
−
*'''Influence of out-gasing from plastics'''
+
Main Article: [[Switching Contacts| Switching Contacts]]
−
Fig. 6.9:
 
−
Histogram of the contact
 
−
resistance R of an electroplated K
 
−
palladium layer (3 μm) with and
 
−
without hard gold flash plating
 
−
(0.2 μm) after exposure with
 
−
different plastic materials
 
  
−
Fig. 6.10: Contact resistance with exposure to out-gasing from plastics as a function of numbers of
+
===<!--6.4.5-->Physical Effects in Sliding and Connector Contacts===
−
operations at 6 V ,100 mA: 1 Silicon containing plastic; 2 Plastics with strongly out-gasing DC
 
−
components; 3 Plastics with minimal out-gasing components
 
  
−
*'''Influence of corrosive gases on the contact resistance'''
+
Main Article: [[Physical Effects in Sliding and Connector Contacts| Physical Effects in Sliding and Connector Contacts]]
  
−
Fig. 6.11: Distribution of cumulative frequency H of the contact resistance for solid contact rivets
+
===<!--6.4.6-->General Rules for Dimensioning of Contacts===
−
after 10 days exposure in a three-component test environment with 400 ppb each of H<sub>2</sub>S, SO<sub>2</sub> and
 
−
NO<sub>2</sub> at 25°C, 75% RH; Contact force 10cN; Measuring parameters: ≤ 40 mV<sub>DC</sub>,10 mA; Probing
 
−
contact: Gold rivet
 
  
−
Fig. 6.8: Influences on contact areas in relays
+
Main Article: [[General Rules for Dimensioning of Contacts| General Rules for Dimensioning of Contacts]]
  
 +
===<!--6.4.7-->Contact Spring Calculations===
  
−
*'''Contact Phenomena under the influence of arcing Matertia'''
+
Main Article: [[Contact Spring Calculations| Contact Spring Calculations]]
−
*'''Material transfer'''
 
−
Fig. 6.12: Material transfer under DC load a) Cathode; b) Anode.
 
−
6 Material: AgNi0.15; Switching parameters: 12VDC, 3 A, 2x10 operations
 
  
−
*'''Arc erosion'''
+
==References==
−
 
 
−
Fig. 6.13 Arc erosion of a Ag/SnO<sub>2</sub> contact pair after extreme arcing conditions
 
−
a) Overall view; b) Partial detail view
 
−
 
 
−
*'''Contact welding'''
 
−
Fig. 6.14: Micro structure of a welded contact pair (Ag/SnO<sub>2</sub> 88/12 - Ag/CdO88/12)
 
−
after extremely high current load. a) Ag/SnO<sub>2</sub> 88/12; b) Ag/CdO88/12
 
−
 
 
−
 
 
−
===6.4.5 Physical Effects in Sliding and Connector Contacts===
 
−
 
 
−
*'''Mechanical wear of sliding contacts'''
 
−
 
 
−
dV/dx = k x FK /3 HW
 
−
3 dV/dx Wear volume in mm per slide path length in mm
 
−
k Coefficient of frictional wear
 
−
HW Hardness of the softer material
 
−
(Brinell or Vickers units)
 
−
FK Contact force in cN
 
−
Wear coefficient k during material transfer
 
−
-4 Silver – Silver 120 x 10
 
−
-4 Platinum – Platinum 400 x 10
 
−
-4 Silver – Platinum 1.3 x 10
 
−
Coefficient of fractional wear k during wear loss
 
−
-4 Silver – silver 8 x 10
 
−
-4 Gold – gold 9 x 10
 
−
-4 Platinum – platinum 40 x 10-
 
−
4 Silver – gold 9 x 10
 
−
-4 Silver – platinum 5 x 10
 
−
 
 
−
Fig. 6.15: Coefficient of frictional wear for the wear loss of sliding contacts Silver/Silver
 
−
and hard gold/hard gold as a function of the contact force
 
−
 
 
−
*'''Contact behavior of connectors'''
 
−
Fig. 6.16: Contact resistance R as a function k
 
−
of the contact force F for different surface k
 
−
coating materials. Measured against a
 
−
spherical gold probe; I = 10 mA, U < 20 mV
 
−
 
 
−
Fig. 6.17: Contact resistance R as a function k
 
−
of the fretting wear cycles for different surface
 
−
coating materials
 
−
 
 
−
Tab.6.4: Surface Coating Materials for Connectors
 
−
 
 
−
 
 
−
===6.4.6 General Rules for Dimensioning of Contacts===
 
−
*'''Recommended Minimum Contact Forces at Slightly Sliding
 
−
Contact Make:'''
 
−
 
 
−
Gold 0.03 N
 
−
Silver 0.1 N
 
−
Tungsten 0.5 N
 
−
 
 
−
*'''Contact Force Recommendations:'''
 
−
 
 
−
Signal relays >3 cN
 
−
AC power relays > 20 cN
 
−
Automotive relays > 20 cN
 
−
Motor switches (Contactors) 0.05 - 0.08 N/A
 
−
(Silver – Metal oxide contacts)
 
−
Power switches 0.1 - 0.2 N/A
 
−
Connectors > 30 cN/contact element
 
−
(Gold coating)
 
−
Connectors > 50 cN/contact element
 
−
(Silver coating)
 
−
Connectors > 1 N/contact element
 
−
(Tin coating)
 
−
 
 
−
*'''General Rules for Dimensioning of Contact Rivets'''
 
−
bild
 
−
 
 
−
*'''Head diameter for electrical loads'''
 
−
 
 
−
For AC currents: approx. 1 – 1.5 A/mm²
 
−
For 1 A min. 2 mm head diameter
 
−
10 A approx. 3 – 3.5 mm head diameter
 
−
20 A approx. 5 mm head diameter
 
−
For DC currents: approx. 0.5 – 0.8 A/mm²
 
−
 
 
−
*'''Head radius R for electrical loads'''
 
−
 
 
−
for I < 1 A R 1,5 mm
 
−
I = 6 A R 5 mm
 
−
I = 10 A R 10 mm
 
−
I = 20 A R 15 mm
 
−
 
 
−
*'''Failure Probability of Single and Double (Bifurcated) Contacts''' (according to Thielecke)
 
−
 
 
−
Fig. 6.18: Failure probability of a contact as a
 
−
function of the voltage (according to Kirchdorfer);
 
−
Ag/Ni10; 10 mA
 
−
 
 
−
Fig. 6.19: Failure probability of a contact as a
 
−
function of the current (according to
 
−
Kirchdorfer); Ag/Ni10; F = 0.45 N; U = 24 V
 
−
 
 
−
===6.4.7 Contact Spring Calculations===
 
−
Fig. 6.20:
 
−
One side fixed contact bending spring
 
−
L = Length of spring
 
−
E = Modulus of elasticity
 
−
B = Width of spring
 
−
F = Spring force
 
−
D = Thickness of spring
 
−
x = Deflection
 
−
max = maximum bending force
 
−
 
 
−
The influence of the dimensions can be illustrated best by using the single side
 
−
fixed beam model (Fig. 6.20). For small deflections the following equation is valid:
 
−
 
 
−
F= x
 
−
3 x E x J
 
−
L³
 
−
 
 
−
where J is the momentum of inertia of the rectangular cross section of the beam
 
−
 
 
−
J=
 
−
B x D³
 
−
12
 
−
 
 
−
For springs with a circular cross-sectional area the momentum of inertia is
 
−
 
 
−
J=BD4/64
 
−
D= Durchmesser
 
−
 
 
−
To avoid plastic deformation of the spring the max bending force σ cannot be max
 
−
exceeded
 
−
 
 
−
Fmax= 3 x E x D xmax
 
−
2L²
 
−
 
 
−
The stress limit is defined through the fatigue limit and the 0.2% elongation limit
 
−
resp.
 
−
 
 
−
xmax= 2 x L ² Rp0,2
 
−
3 x D x E
 
−
 
 
−
and/or
 
−
 
 
−
Fmax= B x D ² Rp0,2
 
−
6L
 
−
 
 
−
 
 
−
*'''Special Spring Shapes'''
 
−
 
 
−
*'''Triangular spring'''
 
−
 
 
−
Deflection
 
−
x= L³
 
−
F
 
−
2 x E x J
 
−
 
 
−
= x L³
 
−
D³
 
−
6 x F
 
−
E x B
 
−
 
 
−
Max. bending force
 
−
Fmax= 1 8 x F x L
 
−
B x D²
 
−
 
 
−
*'''Trapezoidal spring'''
 
−
 
 
−
Deflection
 
−
x= x L³
 
−
E x J
 
−
F
 
−
(2 + B /B )
 
−
 
 
−
x= x L³
 
−
E x B x D³
 
−
12 x F
 
−
(2 + B /B ) min ma
 
−
 
 
−
Max. bending force
 
−
 
 
−
Fmax= 1 8 x F x L
 
−
(2 + B /B ) x B x D² min max max
 
−
 
 
−
 
 
−
===Referencens===
 
  
 
Vinaricky, E. (Hrsg): Elektrische Kontakte-Werkstoffe und Anwendungen.
 
Vinaricky, E. (Hrsg): Elektrische Kontakte-Werkstoffe und Anwendungen.
Line 627: Line 472:
 
Kirchdorfer, J.: Schalter für elektrische Steuerkreise, Blaue TR-Reihe, Heft 91,
 
Kirchdorfer, J.: Schalter für elektrische Steuerkreise, Blaue TR-Reihe, Heft 91,
 
Verlag Hallwag, Bern und Stuttgart 1969
 
Verlag Hallwag, Bern und Stuttgart 1969
 +
 +
[[de:Anwendungstabellen_und_Richtwerte_für_den_Einsatz_elektrischer_Kontakte]]

Latest revision as of 13:41, 10 January 2023

Application Ranges for Switching Contacts

Low and Medium Electrical Loads

Switching processes at low and medium electrical loads are experienced for example in relays and switches for the measuring technology, telecommunications, automotive usage and appliances. The switching voltage ranges from μV to 400V with currents between μA and about 100A.

Main Article: Low and Medium Electrical Loads

High Electrical Loads

With high electrical loads, as usually occuring in power engineering equipment, the switching phenomena are usually due to arcing. For most applications the management of the switching arc is the key problem. Depending on the device type, different requirements are dominant, which influence the selection of the contact material. Similar to those in communications engineering, issues related to the switching characteristics and current path have to be considered.

Main Article: High Electrical Loads

Contact Materials and Design of Contact Components

The highest reliability and electrical life of electromechanical components and switching devices can only be achieved if both, the material selection and the design of the actual contact parts, are optimized. Of course, economic considerations must also be applied when selecting the most suitable contact material and its way of application as an electrical contact. In the following Table 1 recommendations are made for selected application examples for contact materials and contact shape or configuration.

Table 1: Material Selection and Contact Component Design
Type of Contacts or Devices Characteristic Requirements for Contacts Contact Material Design Form of Contacts
Contacts for dry circuits Reliable contacting at very low currents and voltages and mostly at also
low contact forces 		AuAg alloys, (AuPt), Au Contact rivets, welded miniature profiles (tapes), electroplated Au, sputtered Au layers
Switching contacts in measuring devices Reliable switching at low voltages and currents at low contact forces Au and Pt alloys, (AgPd alloys) Contact rivets, welded tips, clad parts
Keyboard contacts Defined contacting, close to bounce-free make, high reliability at low switching loads Au alloys, (AgPd), Au on Ni substrate Au plated snap discs, Au clad wires and stamped parts, hard gold electroplated contact spots on printed circuit boards
Rotary switches on printed circuit boards Good frictional wear resistance, low contact résistance Sliding track: hard gold on Ni substrate Slider: AgPd alloy, (Hard silver) Electroplated coatings on slide tracks; clad, welded, or riveted stamping parts
Slip rings with high reliability Low and consistent contact resistance at low contact forces Brushes: Au alloys, AgPd, AgPdCu; Slip rings: Au alloys, Ag alloys (Rh); For higher currents: Ag/C brushes against Ag slip rings Brush wires, stamped brushes; solid, clad, or electroplated slip rings, Ag/C formed parts
Sliding contacts in miniature motors Very high frictional wear resistance, sure contacting even at very low contact forces Ag and Au alloys, Pd alloys, Au multi component alloys Brushes from flat rolled wire or stamped; collector hard gold electroplated or clad; made from miniature profile segments
Centrifugal controllers for small motors Little shape changes, defined contacting at very low contact forces and high frequency of operation Pd alloys Contact rivets, contact screws, welded parts
Connectors Low contact resistance, corrosion resistance, sufficient frictional wear resistance, good sliding capabilities Ag and Au alloys, Pd, PdNi; For automotive and consumer electronic at low operation numbers: Sn and Sn alloys Electroplated layers or clad, often Au flash plated, mostly with Ni substrate layer, stamped parts from hot tin dipped strip
Telecommunication relays Reliable contacting even at high operational frequency Ag, AgPd, Au alloys, PdRu Rivets, welded profile segments
Reed relay contacts High reliability at low currents independent of atmospheric environment Au, (Rh) Switch paddles FeNi with partially diffused Au, (electroplated Rh)
Relays in electronic circuits High reliability at low switching loads and compact device design Au alloys, AgPd, Ag alloys Stamped springs from seam-welded profiles, welded miniature profile (tape) segments, contact rivets
GP relais (Elementary relays) Low arc erosion, high weld resistance, low and consistent contact resistance Ag/Ni, Ag/SnO2, (Ag/CdO), Ag/ZnO,AgNi0.15, (Ag) Solid and composite contact rivets, welded miniature profile (tape) segments
Automotive relays Low material transfer, low contact resistance, high weld resistance AgNi0.15, Ag/SnO2, Ag/Ni Contact rivets, welded miniature profile (tape) segments
Flasher relays (automotive, > 3 Mio operations) Low material transfer, high arc erosion resistance, low contact resistance PdCu15 and 40 (Anode) vs. AgNi0.15, AgCu3 (Cathode), Ag/ZnO, Ag/SnO2 Contact rivets, welded miniature profile (tape) and strip segments
Breaker points (automotive ignition) Very high arc erosion resistance, high switching frequency W Tips or discs welded to formed parts or Fe supports
Automotive horn contacts High arc erosion resistance at extremely high number of switching operations W, Ag/SnO2 Contact rivets, W weld buttons, springs or formed parts with brazed or welded tips
Appliance switches Low contact resistance, reasonable arc erosion and weld resistance AgNi0.15, Ag/Ni, Ag/SnO2, (Ag/CdO) Contact rivets, welded contact parts
Temperature controllers (Thermostats) Defined contacting point even at slow motion make, high operating temperatures AgNi0.15, Ag/Ni, Ag/SnO2, (Ag/CdO) Contact rivets, welded contact parts, weld buttons
Wiring devices (Light switches) Low contact resistance, reasonable arc erosion and weld resistance AgNi0.15, AgCu, Ag/Ni, with make peaks also Ag/ZnO, (Ag/CdO) Contact rivets, welded contact parts


Table 1: Material Selection and Contact Component Design (Fortsetzung)

Type of Contacts or Devices Characteristic Requirements for Contacts Contact Material Design Form of Contacts
Automatic staircase lighting switches High arc erosion and weld resistance Ag/Ni, Ag/SnO2, (Ag/CdO), Ag/C against Ag/SnO2 Rivets, welded contact parts
Miniature Circuit breakers Extremely high weld resistance, low temperature rise in use, sufficient arc erosion resistance I< 50 A: Ag/C97/3 (Cu/C) against Cu, I> 50 A : Ag/C97/3 o. 95/5 against AgCu3, Ag/Ni90/10 o. 80/20, Ag/W, Ag/WC (USA) Welded contact parts (Ag/C), clad stamped parts
Fault current circuit breakers Extremely high weld resistance, low contact resistance, high arc erosion resistance Stationary contact: Ag/C96/4 o. 95/5 Movable contact: Ag/Ni, Ag/MeO, Ag/W, Ag/WC, Ag/WC/C Welded and brazed contact parts
Micro snap switches Low contact resistance, no sticking during make operation AgNi 0,15, Ag/Ni, Ag/SnO2, (Ag/CdO) Rivets, clad or welded contact parts
Control and auxiliary switches Low contact resistance over extended life span Ag, AgNi 0,15, AgCu, Ag/Ni Rivets, clad stamped parts, (gold plated rivets), welded contact parts
Auxiliary and control relays High reliability over extended life span, low contact resistance AgNi 0,15, Ag/Ni Rivets, clad profile parts, welded contact parts
Cam switches (higher loads) High arc erosion and weld resistance, low contact resistance AgCu, Ag/Ni, Ag/SnO2, Ag/ZnO, (Ag/CdO) Rivets, welded contact parts
Contactors High arc erosion and weld resistance, low contact resistance I< 20A : Ag/Ni, Ag/SnO2 I>20A : Ag/SnO2, (AgCdO) Welded and brazed contact tips
Motor -protective circuit breakers Extremely high weld resistance, low contact resistance Ag/ZnO, Ag/C against Ag/Ni Welded contact parts, toplay stamping parts
Power switches and circuit breakers Extremely high arc erosion and weld resistance, low contact resistance Ag/ZnO, Ag/SnO2 , Ag/C against Ag/Ni o. Ag/W, Ag/W, Ag/WC/C, Ag/W against Ag/CdO Brazed and welded contact tips and formed parts
Power switches with arcing and main contacts High weld resistance, low contact resistance, high arc erosion resistance Arcing contacts: W/Ag, W/Cu, (Cu) Main contacts: Ag/Ni, Ag/ZnO, Ag/W, Ag/WC Brazed and welded contact tips and formed parts
Disconnect switches Low contact resistance, sufficient mechanical strength AgNi 0,15, Ag/Ni, Ag (electroplated) Electroplated coatings, brazed contact parts
High voltage circuit breakers Arcing contacts: highest arc erosion resistance Main contacts: low contact resistance Arcing contacts: W/Cu-infiltrated Main contact CuCrZr silver plated, Cast-on, electron-beam welded (or brazed) formed parts, percussion welded pins
Load disconnect switches (medium and high voltage) Low contact resistance, sufficient mechanical strength, high arc erosion resistance of precontacts Arcing contact: W/Cu, Cu, Ag/C Main contact: Cu, CuCrZr silver plated, Ag/Ni, AgNi0,15, Ag/C Arcing contacts: brazed or welded parts Main contacts: silver plated, brazed or welded parts
Vacuum contactors Low chopping current, high arc erosion resistance, low contact resistance Low gas content W/Cu, W/CuSb, WC/Ag, CuCr Contact discs, shaped rings
Vacuum circuit breakers High switching capacity, low contact resistance Low gas content CuCr Contact discs
Transformer tab changers High arc erosion resistance in oil environment W/Cu in filtrated with approx. 70% Brazed contact tips
Disconnect switches in high voltage circuits Low contact resistance, low mechanical wear, sufficient arc erosion resistance during current commutation Ag (electroplated), AgNi0,15, Ag/SnO2 Electroplated coatings, brazed parts, Toplay profile segments

Notes: Table 1 is meant to give suggestions for the use of contact materials for the specified devices. For most of the contact materials, we deliberately did not indicate the exact composition and, as for Ag/SnO2 and AgZnO, did also not include specific additives. The final material composition depends on specific design parameters of the electrical device. Advise on the special properties of specific contact materials can be found in chapter 2 Contact Materials for Electrical Engineering .

Design Technologies for Contacts

A multitude of technologies is available and used for the actual manufacturing of contact components (see chapter 3 Manufacturing Technologies for Contact Parts). The desired contact shape however, requires specific material properties like formability and weldability, which cannot be fulfilled by all materials in the same way. In addition, the design of the contact part must be compatible with the stresses and requirements of each switching device. The following Table 2 combines contact design, contact material and specific applications.


Table 2: Design Technologies for Contacts
Contact Parts, Semi-finished Materials Typical Contact Materials and Dimensions Main Areas of Application Remarks
Contact rivets solid, inserted wire segments Ag, Ag alloys, Au alloys, Pd alloys, Ag/Ni, Ag/C97/3, Ag/MeO (1.2 – 8 mm Ø) All types of switches in the communications, automotive or power distribution technology simple contact component, universally applied, selection through economic aspects Secure rivet attachment only with sufficiently thick shank (shank Ø = 1⁄2 head Ø); change-over contacts by forming secondary head from longer shanks
Contact rivets, clad (Composite Rivets) Ag, Ag alloys, Ag/Ni, Ag/MeO on Cu base (2 ~ 10 mm Ø) All types of switches in the communications, automotive or power engineering Secure rivet attachment only with sufficiently thick shank (shank Ø = 1⁄2 head Ø)
Contact rivets with brazed surface layer Tungsten and difficult to form powder metallurgical materials (i.e. Ag/C) on Cu or Fe bases (1 ~ 12 mm Ø) Switches for power engineering, W layers mostly for controls Tungsten contact to be staked (riveted) with moderate force or using orbital riveting; for Fe bases also warm-forming
Contact screws Any contact material on Fe and CuZn screws, brazed, (1 ~ 10 mm Ø, M 2 ~ M 10) Adjustable contacts for controls and horns During brazing carrier may get soft
Vertically welded wire segments Ag, Ag alloys, Ag/Ni, AgPd, Au alloys (wire 0.6 ~ 5 mm Ø) Contact parts for control functions and power engineering; economical manufacturing at higher quantities Welding and subsequently heading or orbital forming of head shape
Horizontally welded wire and profile segments Au alloys, Pd alloys, Ag, Ag alloys, Ag/Ni, Ag/MeO, Ag/C in strip or profile form, Miniature profiles - also multi-layered (profile width 0.2 ~ 5 mm) Contact parts for communication, measurement, controls and power engineering; very economical with respect to precious metal usage Welding synchronized to stamping / forming on special equipment
Weld buttons Ag, Ag alloys, Ag/Ni, Ag/MeO on Steel, Ni, Monel; Ag/W, Ag/Mo (1.5 ~ 10 mm Ø) Welded for example to steel springs or thermostatic bimetals for temperature controls Metallurgical bond through simple projection welding remains strong in temperature cycling applications
Tungsten weld buttons W on Ni or Ni-plated Fe, (2 ~ 6 mm) with weld projections Contacts for controls, ignition points and horns; arcing contacts in special relays For change-over contact welded on both sides of carrier
Brazed contact tips All materials and dimensions, oxide and graphite containing materials with brazable backing, carrier parts from Fe, Cu and Cu alloys, at higher strength requirements also CuCrZr or CuBe Medium and higher load switching devices for power engineering Braze alloy layer with low meting point, carriers may soften during brazing
Clad contact materials (Contact Bimetals), totally covered or with inlayed strips Ductile precious metals on Cu and Cu alloys, minimum precious metal layer 2% of total strip thickness for Ag and Ag alloys, 0.5% of total strip thickness for Au alloys (with Ni intermediate layer), max. inlayed thickness 50% of total, strip width starting at 2 mm Clad contact springs; stamped and formed parts for communications and power engineering; aluminum clad for bonding capability Metallurgical bond; inlayed strip stamped perpendicular or at angle to strip direction; avoid bends at the cladding edges
Strips or profiles with brazed contact material layers (Toplay material) Ag, Ag alloys, Ag/Ni, Ag/MeO on Cu and Cu alloy carriers, total width 10 ~ 100mm, carrier thickness 0.3 – 5 mm, Ag strip cross section from 0.3 x 3 mm2, strip thickn. to be ≤ carrier thickn. Stationary and moving contact bridges for power engineering switching devices Contact layers brazed with Ag brazing alloys; strips re-hardened during profile rolling
Seam-welded contact strips or profiles Wire, strip, miniature profiles (solid or clad) welded to Cu alloy carrier strip (0.3 – 3 mm Ø or up to 5 mm width) Switches, pushbuttons, relays, auxiliary contactors, sliding contacts Broad usability, highly economical, thin spring hard carriers can be used
Miniature profiles (Weld tapes) Mostly high precious contact materials, double or multi layer, Ni, Monel, or Cu alloy carrier; miniature-profile width 0.2 – 2 mm Welded profile segments for contact parts in communication, measurement and control engineering Manufacturing of cross-directional contact spots; most economical precious metal usage


Table 2: Design Technologies for Contacts (Fortsetzung)

Contact Parts, Semi-finished Materials Typical Contact Materials and Dimensions Main Areas of Application Remarks
Clad profiles Ag, Ag alloys, Ag/Ni, Ag/MeO, on Cu or Cu alloy carriers, all cross-sectional areas that can be drawn or rolled; Profile width: 2 ~ 10 mm Profile segments as contact areas for low and high voltage switching devices More complex shapes require costly tooling
Sintered and infiltrated parts W-, WC-, Mo-based materials, in almost any contact shapes Contact parts for low and high voltage switching devices Single parts pressing; mostly with weld projec- tions and braze alloy coating on underside
Formed arc erosion parts W/Cu infiltration materials, parts in almost any shapes Arcing contacts for extreme duty switching devices, i.e. SF6 circuit breakers Attachment to Cu carriers by cast-on, percussion welding, electron-beam welding; rarely by brazing
Low gas content contact parts W/Cu-, WC/Ag-, CuCr-based materials, rings and discs in almost any shape Shaped contact parts for vacuum switches (contactors, power switches, circuit breakers) Brazing to Cu carriers requires special brazing alloys
Cast-on contact parts W/Cu cast on with Cu, shaped parts and rings up to 100 mm Ø Arcing contacts in high voltage switchgear Seamless bond interface, carriers get hardened through subsequent forming
Electron-beam welded contact parts W/Cu on Cu or CuCrZr contact rods, tubes, tulips Arcing contacts in high voltage circuit breakers Seamless bond interface, withstands high mechanical and thermal stresses
Silver electroplating Layer thickness up to 20 μm, mostly on Cu and Cu alloys Connecting areas and no-load switching contacts in power engineering; rotary switches, sliding contacts, connectors For switching contacts only under very low loads
Gold electroplating Flash plating 0.1 – 0.2 μm on Ag alloys, and Cu alloys; contact layers 0.5 – 5 μm mostly with intermediate Ni layer Contacts with low current and voltage loads, connectors, rotary and sliding switches, contact areas on printed circuit boards Flash plating only limited effective as corrosion resistant layer on silver contacts
Selectively electroplated strips Stripe coatings: Tin plating 1- 10 μm, Ag plating 1 – 20 μm, Au plating 0.2 – 5 μm; stripe width 2 mm min, stripe distance > 2 mm; carrier material: Cu and Cu alloys, Ni alloys, stainless steel; strip thickness: 0.1 ~ 1 mm; strip width: 5 ~ 100 mm Contact parts for connectors, keyboard switches, rotary and sliding switches; bondable areas (Au) for electronic components Economic manufacturing for partially plated parts; hard gold with Ni intermediate layer possible but has limited formability
Selectively electroplated pre-stamped strips, Spot gold plating Continuous partial electroplating of pre-stamped and coined contact spots; all

precious metals; intermediate layers of Cu or Ni; selective tinning of connector contact areas and terminal ends; carrier materials up to 1 mm thick, strip width up to ~ 80 mm

Precious metal plating of switching contacts, connector parts, and terminal pins in the communication technology Crack-free and wear resistant layers possible since contact areas are already formed to final shape
Sputtered profiles Au, Au alloys in any composition; layer thickness 0.1 – 5 μm Contact profiles for relays, switches and keyboard contacts in the information and measuring technology High purity contact layers for high reliability
Hot-dip tinned strips All around or stripe tinning 1 ~ 15 μm Connectors for automotive and consumer technology; screw and crimp connectors Economic coating method; does not form (Sn) whiskers

Formulas and Design Rules

Definition of Terms and Symbols

Note: The symbols for electrical contact specific terms (i.e. contact area, contact resistance, etc. have been retained from the german version of the Data Book. In related English literature some of them may vary using subscript symbols related to the language used – for example “contact resistance”: as used here from german Rk, in english mostly Rc.

Main Article: Definition of Terms and Symbols

Contact Physics – Formulas

Main Article: Contact Physics – Formulas

Closed Contacts

Figure1: Rough flat surface. a) before and b) during making contact with an ideally smooth flat surface; c) Schematic of the apparent, load bearing and effective contact areas (not to scale; dashed lines are elevation lines)
Figure 2: Contact resistance of crossed rods as a function of the contact force for gold, silver and silver-palladium alloys


Table 3: Thermo-electrical Voltage of Contact Materials (against Copper)
Contact Materials Thermo-electric Voltage (0 - 100°C) [mV]
Pure metals Ag
Au
Pt
Ir
Pd
Rh
Re
Cu
W
Mo 		+ 0.04
+ 0.06
+ 0.78
+ 0.13
+ 1.35
+ 0.08
+ 0.78
0
- 0.46
- 0.73
Alloys/Composite materials AgCu 3
AgPd 30
AgPd 40
AgPd 50
AgPd 60
Ag/Ni 10
Ag/Ni 20
Ag/W 65
AuNi 5
AuAg 20
AuPt 10
PtW 5
Ptlr 10
Ptlr 20
PtRu 5
PtRu 10
PdCu 15
PdCu 40 		+ 0.026
+ 0.125
+ 0.198
+ 0.321
+ 0.412
+ 0.23
+ 0.27
+ 0.01
+ 4.7
+ 2.76
+ 1.11
+ 0.67
+ 0.56
+ 0.60
+ 0.32
+ 0.13
+ 0.180
+ 0.247

Switching Contacts

Main Article: Switching Contacts

Physical Effects in Sliding and Connector Contacts

Main Article: Physical Effects in Sliding and Connector Contacts

General Rules for Dimensioning of Contacts

Main Article: General Rules for Dimensioning of Contacts

Contact Spring Calculations

Main Article: Contact Spring Calculations

References

Vinaricky, E. (Hrsg): Elektrische Kontakte-Werkstoffe und Anwendungen. Springer-Verlag, Berlin, Heidelberg 2002

Schröder, K.-H.: Grundlagen der Werkstoffauswahl für elektrische Kontakte. Buchreihe „Kontakt & Studium“, Band 366:zit. in „Werkstoffe für elektrische Kontakte und ihre Anwendungen“, Expert Verlag, Renningen, Bd. 366, (1997) 1-30

Horn, J.: „Steckverbinder“. zit. in Vinaricky, E. (Hrsg): „Elektrische Kontakte- Werkstoffe und Anwendungen“, Springer-Verlag, Berlin, Heidelberg 2002, 401- 419

Holm, R.: Electric Contacts, Springer-Verlag, Berlin, Heidelberg, New York 1967

Sauer, H. (Hrsg): Relais-Lexikon. 2. Aufl. Hüthig-Verlag, Heidelberg 1985

Greenwood J.A.: Constriction Resistance and the Area of Contact, Brit.J.Appl.Phys. 17 (1966) 1621

Biefer, H.: Elektrische Kontakte, Technische Rundschau (Bern) (1954/10) 17

Thielecke, K.: Anwendung von Kontakten in Schwachstromschaltern, in “Kontaktwerkstoffe in der Elektrotechnik”, Akademie-Verlag Berlin 1962, 107

Kirchdorfer, J.: Schalter für elektrische Steuerkreise, Blaue TR-Reihe, Heft 91, Verlag Hallwag, Bern und Stuttgart 1969

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