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Home > Technology > Safety Requirements    
Safety Requirements

  Safety requirements must be taken into full consideration when designing or purchasing relays, particularly those with medium or high power. The safety of the relays lies mainly in the following three aspects:

1. Insulation material
  The insulation material must be fire-retardant: resistance to maximum temperature 3 maximum ambient temperature + coil temperature rise + 15°C

2. Contact overload capacity
  The contact must be capable of switching double rated load current 100 times (200 times for alternating current).

3. Insulation dielectric strength
  Generally, insulation resistance between various conducting parts of the relay must be: >100MW; > 500MW; > 1000MW; > 10000MW. The insulation between various conducting parts of the relay must be able to withstand the maximum peak value which is likely to occur during operation without any damage; the leakage current must not exceed 100mA (or 1mA); flashover, sparkover or breakdown must be prevented to avoid damage. Special caution must be exercised regarding the withstand voltage between the coil and the contact as well as the critical creepage distance. The withstand voltage between the coil and the contact generally must exceed 4000Vac when the contact of the relay switches 220v or 380v inductive loads.

Requirements of Failure Rates
  In certain circumstances, the relay in operation must meet a very high standard of reliability. For example, relays installed in satellite, rockets, missiles, airplanes and program-controlled switches must have a failure rate up to Level L (1X10-6) or Level Q (1X10-7). Data of failure rates are as follows:

Equivalent of US-Military
Standard Failure Rates
Level Symbols
of Failure Rates
Level Failure
Rates
Maximum Permissible
Failure Rates l 1/10 times

L
M
P
YW
W
L
Q
Level V
Level V
Level VI
Level VII
3×10-5
1×10-5
1×10-6
1×10-7

  Relays with failure rates may cause the cost to rise dramatically. Caution is required when the customer requests the relay to meet certain failure rates.

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