Required upstream protection of an ATS

[philly]

It is my understanding that for an ATS per its UL listing an upstream OCPD is required in order to clear faults within the ATS specific withstand rating. I cam across a situation where an ATS is fed on the normal side directly from the secondary of a transformer with no OCPD between the transformer secondary and ATS. The emergency side of the ATS has an OCPD located upstream at the generator however there is no OCPD located on the normal side.

Is it correct that an OCPD is required to be located upstream of the ATS on the normal side according to its UL listing?

 

[buddhakii]

Is this ats located on the secondary side of the poco transformer? If so either you will need a service disconnect or a service rated ats which I'm assuming you don't have. If not then you are asking a good question because I have no clue. It would seem to me you would want to protect the ats though.

 

[augie47]

Can you provide some more detail on the installation ?
Is the "normal" supply a service ? or is this a customer transformer ?
In almost every scenario I can think of, a disconnect would be required if the ATS is not so equipped, due to the rules in Art 230 and 240, but there could possibly be a commercial/industrial situation with delta/delta transformers which would be different.

 

[philly]

Can you provide some more detail on the installation ?
Is the "normal" supply a service ? or is this a customer transformer ?
In almost every scenario I can think of, a disconnect would be required if the ATS is not so equipped, due to the rules in Art 230 and 240, but there could possibly be a commercial/industrial situation with delta/delta transformers which would be different.

The "normal" supply is not a service but rather is a customer delta-wye transformer located downstream in a customers system. The normal source if fed from a 500kVA customer transformer while the emergency side is fed fom an emergency generator. The load side of the ATS only serves on MCC.

 

[augie47]

If the transformer is a XO bonded wye secondary then 240.21(C) is going to require OCP for the transformer secondary condcutors. That same OCP device, if in the same building, can serve as your ATS disconnecting means.
I see no 240.21(C) rule that would allow the ATS alone (without OCP) to provide protection for a wye secondary.

 

[philly]

If the transformer is a XO bonded wye secondary then 240.21(C) is going to require OCP for the transformer secondary condcutors. That same OCP device, if in the same building, can serve as your ATS disconnecting means.
I see no 240.21(C) rule that would allow the ATS alone (without OCP) to provide protection for a wye secondary.

Immediately after the ATS there is an MCC with a 600A main breaker. Would this main breaker in the MCC be allowed to protect the cable between the transformer and the ATS if the cable was an adequate size. In this case the cable is a 535 kCMIL DLO cable with an ampacity of 728A so this cable could be protected by the 600A MCC main breaker if this breaker was allowed to protect this upstream cable?