Automatic Transfer Switch Withstand Ratings

[steve66]

I'm reviewing some shop drawings for a generator and ATS. The ATS Withstand Ratings are only for specific circuit breakers. The ATS doesn't have any withstand rating for use with current limiting fuses, and no ratings for "Any Breaker".

The problem is that the main breaker on the generator isn't one of the listed circuit breakers.

I know the generator will only provide a limited amount of fault current, usually less than 8-10X the generator current rating, which in this case, would probably be less than 5000 amps.

But still, doesn't the ATS need to be used with one of its listed breakers?

 

[jim dungar]

But still, doesn't the ATS need to be used with one of its listed breakers?

The issue is usually the rating of the Normal source fault current not the generator.

For some reason the listed device ratings are not often included with switch submittal data. We often only get a reference to the part number of the label that is shipped with the switch, requiring us to ask for additional submittals.

 

[ron]

As mentioned by Jim, you will need to ask for more info. The ATS likely has a withstand rating without a breaker even though it will be low, it may be low enough for the generator.

The normal source will generally be the worst case for the condition and be sure that has the required breaker to get the withstand rating you need.

 

[Jraef]

As to the specific breaker issue, what happens is that the ATS mfr only submitted it to UL (or some other NRTL) with that specific breaker, not wanting (or knowing) to pay extra for the testing required to allow anything else. This often happens with low-end players who are basically putting that burden off into the user to keep their costs down, or foreign mfrs who don’t understand how the NRTL listing system works.

 

[steve66]

OK, I'll check and see if there is some low withstand rating without a breaker.