Installing ATS

[utilguy]

We're installing an auto transfer switch ahead of an existing main service panel. The 2 feeds will be from separate padmounted transformers on different distribution systems. The neutral conductors would normally be grounded in the transformers. The plan is to install service entrance disconnects between each transformer and the ATS. It seems the neutrals should be grounded and bonded in each new service disconnect (correct?) but would there need to be changes made in the existing service panel too?
thanks

 

[ceb58]

We're installing an auto transfer switch ahead of an existing main service panel. The 2 feeds will be from separate padmounted transformers on different distribution systems. The neutral conductors would normally be grounded in the transformers. The plan is to install service entrance disconnects between each transformer and the ATS. It seems the neutrals should be grounded and bonded in each new service disconnect (correct?) but would there need to be changes made in the existing service panel too?
thanks

The N-G bond would be in the first disconnecting means. Any thing after that would have the neutral isolated and EGC to the enclosure.

 

[augie47]

I agree. If the Neutral was bonded in the original service disconnect it must be seperated from any grounding.
The only exception I can think of would be if you currently fall under the 250.32 exception.

 

[hurk27]

We're installing an auto transfer switch ahead of an existing main service panel. The 2 feeds will be from separate pad mounted transformers on different distribution systems. The neutral conductors would normally be grounded in the transformers. The plan is to install service entrance disconnects between each transformer and the ATS. It seems the neutrals should be grounded and bonded in each new service disconnect (correct?) but would there need to be changes made in the existing service panel too?
thanks

A hospital? ISP Server center?

Much depends on where the utility stops, and the customer begins, if this is being installed by the utility, and they own it, then the NEC might not apply, and the existing service panel stays as just that.

Basically you have two redundant utility services, each new disconnect will require a MBJ, after this point the grounding and grounded conductors must be kept separate including at the ATS, which will mean at the existing panel, if the grounding conductors were landed on the neutral bar, they will have to have a bar of their own and the MBJ in the existing panel will also have to be removed, now as for the grounding electrode conductors, they also will have to be moved to the new MBJ point, which is these disconnects, I would say running them to one disconnect then tap to the other, but at least one GEC in each would have to be continuous?

Roger on here does hospitals so maybe he can chime in?

 

[utilguy]

Thanks for these helpful comments. The installation is at a university IT network operations center. One system is the local utility. The other is the university's own distribution system. The university is installing the equipment.