Controlgear short circuit capacity

[sysengineer]

Supposing a standard DOL motor control circuit. If the utilization category of the contactor for example specifies it's capability to withstand overload currents as multiples of the rated current. What rating determines the ability for it to withstand short circuit currents in the time it takes for the short circuit protective device to clear?

In other words at a given short circuit current the short circuit protective device will take t seconds to clear the fault. How can you be certain the contactor can withstand this current for this amount of time?

- Dan

 

[ScottyUK]

IEC 60947 describes type-tested combination starters where a contactor, overload relay and fuse or breaker have been proven as a group to have characteristics matched to each other to prevent damage. It further describes Type 1 and Type 2 Coordination where Type 1 allows components to be damaged during a through-fault, while Type 2 does not permit material damage to occur. Now you have a couple of things to look for in Google. Here's one to start off with:

http://www.reykjafell.is/gogn/1andtype2coordination.pdf