Inserting ATS in existing service entrance

[philly]

I'm looking at an application we a cusotmer wants to add a new 480V ATS with generator provision to an existing service. Existing service is a 1200A service with utility padmount feeding 1200A SWBD. Our plan was to intercept the existing underground SE conductors between the transformer and the existing switchboard and insert a SE rated ATS with breakers that we would then re-terminate the existing SE conducotrs to the load side of the ATS.

The issue was broght up that with the existing SE condcutors being 4-wire, when we insert the ATS we will not have an Equipment ground conductor (EGC) between the ATS and the existing switchboard. If there were no requirements for 277 L-N loads off of the existing SWBD then perhaps we could use the existing grounded conductor as an oversized EGC but not sure if there is a need for any L-N loads off of the existing Switchboard (4-Wire SWBD).

Are there any NEC provisions that I may be overlooking here related to the need to add an EGC between the ATS and SWBD for this application?

 

[GoldDigger]

If the existing underground is in a metallic conduit, that will be a compliant EGC conductor.

 

[LarryFine]

The issue was broght up that with the existing SE condcutors being 4-wire, when we insert the ATS we will not have an Equipment ground conductor (EGC) between the ATS and the existing switchboard. If there were no requirements for 277 L-N loads off of the existing SWBD then perhaps we could use the existing grounded conductor as an oversized EGC but not sure if there is a need for any L-N loads off of the existing Switchboard (4-Wire SWBD).

Are there any NEC provisions that I may be overlooking here related to the need to add an EGC between the ATS and SWBD for this application?

As usual, on the line side of the ATS, the neutral is the only grounding conductor. The SE-rated ATS becomes the service main disconnect, so the load side must include an EGC.

If there is no neutral required by any load, the neutral may terminate at the ATS and only an EGC continue from that point.

As long as you're sure no neutral is required by the load, your plan sounds compliant. If a load neutral is required, you will need to add a conductor after the ATS.

 

[augie47]

agree with Larry and might add, your grounding electrode conductors will need to move to your service rated ATS if they are no at the existing service board..

 

[ActionDave]

My first choice would be not using a transfer switch as a service disconnect. This solves a lot of problems at the front end and makes any maintenance easier in the long run.

 

[philly]

If the existing underground is in a metallic conduit, that will be a compliant EGC conductor.

I had considered this but assumed that existing UG ductbank of several hundred feed would be PVC conduit. Does anyone see a reason not to assume this for SE conductors in an underground ductbank?