General Rules for Dimensioning of Contacts

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) (Silver – Metal oxide contacts)	0.05 - 0.08 N/A
Power switches	0.1 - 0.2 N/A
Connectors (Gold coating)	≥ 30 cN/contact element
Connectors (Silver coating)	≥ 50 cN/contact element
Connectors (Tin coating)	≥ 1 N/contact element

• General Rules for Dimensioning of Contact Rivets

Dimensioning	Solid Rivets (1)	Composite Rivets (2)
a : d	1.5 : 1 bis 2.5 : 1	2 : 1 bis 2.5 : 1
a : b	2.5 : 1 bis 10 : 1	3 : 1 bis 5 : 1
c : b	≥ 1 : 1	≥ 1 : 1
b : s		≥ 2 : 1
smin		≈ 0.3 mm

• 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)

Contact force[N]	Single contact
	Ag	AuNi 5, Pt	Ag	AuNi 5, Pt
0.04		1 x 10-4		2 x 10-8
0.1	2 x 10-3	4 x 10-5	8 x 10-5	8 x 10-9
0.2	1 x 10-4	8 x 10-6	4 x 10-6	4 x 10-8
0.3	5.5 x 10-6	1.5 x 10-6	1.8 x 10-7	3.2 x 10-10

Figure 1 Fig. 6.18: Failure probability of a contact as a function of the voltage (according to Kirchdorfer); Ag/Ni10; 10 mA

Figure 2 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

References

References