Series Rating through ATS

[pzrapnbeast]

So for the past few years we've only applied series ratings using the immediate next upstream device. So for instance a branch breaker with the main or remote main. If there is an ATS between these two devices then we did not consider this an applicable situation for series ratings. I've recently changed companies and they don't seem to follow this same procedure. I haven't been able to find any documentation verifying either practice. I'm thinking my former company may have just been taking an overly conservative approach. Does anyone have any insight on to the series rating practices of going through an ATS or isolation transformer? If you have references then that would be great.

Thank You

 

[don_resqcapt19]

Assuming that the ATS is rated for the full available fault current, I don't see an issue.

 

[ron]

I don't see any active elements adding complexity to using a series rating through an ATS.

I would definitely question applying series rated devices across the primary / secondary of a transformer. The transformer adds impedance and the fact that it is a separately derived source, makes them essentially separate systems.

The transformer hopefully adds enough impedance that you can use the fully rated value for the device on the secondary on its own without an upstream device.

 

[jim dungar]

It depends on the ATS. For example; an ATS that contains breakers, which might open during a fault, would definitely affect series ratings.

If you are designing systems, but have no control over the final equipment purchased, the conservative approach is to assume the ATS will have an effect.

 

[don_resqcapt19]

Good point Jim...I was not thinking of an ATS with breakers, but that is a common design.

 

[ron]

Good point Jim...I was not thinking of an ATS with breakers, but that is a common design.

Me too, good catch