ATS and Transformer Primary Disconnect

[teh_engineer]

If the primary side of a transformer is connected to the load side of an ATS, would a disconnect be required, or does the disconnects at the supply and generator side suffice?

If not required, would one be practical, but not required, so that the ATS can be fully disconnected in case it needs to be serviced or replaced?

Thanks in advance.

 

[infinity]

Transformer primaries do not require disconnecting means just a label that states where the disconnecting means is located. The ATS doesn't require a disconnect either. It would be a design option if you wanted to use them or not.

 

[david luchini]

To add to what Rob said, if the disconnecting means for the the transformer is located out of sight from the transformer, with a label at the transformer noting the location of the disconnecting means, the disconnecting means shall be capable of being locked in the open position.

 

[teh_engineer]

Thank you for the replies.

The ATS and transformer (75kVA, 480-208V) are in the same room and within sight of each other. The ATS is fed from a circuit breaker at the main panelboard (also same room), and has an enclosed circuit breaker on the generator side, but nothing between the load side and the transformer. The transformer secondary protection is within 10' of the transformer.

I was under the impression that based on 450.3(B), I would need an overcurrent protection device at the transformer primary side and that the secondary is the side that is conditional.

I think another way to frame my question is that if the ATS was not present, I would provide a 125A disconnecting means on the primary side, so it stands to reason (to me anyways) that with the ATS present, I would still need the 125A disconnect on the primary side of the transformer. But do the disconnects upstream of the ATS qualify, or do I need a separate device directly on the primary side of the transformer, or is it not required?

 

[m sleem]

Thank you for the replies.

The ATS and transformer (75kVA, 480-208V) are in the same room and within sight of each other. The ATS is fed from a circuit breaker at the main panelboard (also same room), and has an enclosed circuit breaker on the generator side, but nothing between the load side and the transformer. The transformer secondary protection is within 10' of the transformer.

I was under the impression that based on 450.3(B), I would need an overcurrent protection device at the transformer primary side and that the secondary is the side that is conditional.

I think another way to frame my question is that if the ATS was not present, I would provide a 125A disconnecting means on the primary side, so it stands to reason (to me anyways) that with the ATS present, I would still need the 125A disconnect on the primary side of the transformer. But do the disconnects upstream of the ATS qualify, or do I need a separate device directly on the primary side of the transformer, or is it not required?

It's not that difficult for maintenance where you could have,
- Manual bypass switch.
- Drawable ATS.