Service Entrance ATS and a Life Safety ATS

[Platinum]

Hey guys,

I have a service entrance rated ATS backing up the main switchboard (2000A) and have a separate life safety ATS (400A) for the life safety loads (EM lights). The generator has 2 output breakers feeding these ATS's.
Can a Article 700 (Life Safety) transfer switch be downstream of a Article 702 (Optional STBY) transfer switch?

700.10(B) separation of wiring comes to mind. We will have complete isolation on the emergency side but on the normal side of the LS ATS is fed from the main switchboard, so we will not have isolation.
Also, the downstream LS ATS will always see utility due to the upstream ATS backing up the main switchboard, so it wont ever transfer!

 

[texie]

Hey guys,

I have a service entrance rated ATS backing up the main switchboard (2000A) and have a separate life safety ATS (400A) for the life safety loads (EM lights). The generator has 2 output breakers feeding these ATS's.
Can a Article 700 (Life Safety) transfer switch be downstream of a Article 702 (Optional STBY) transfer switch?

700.10(B) separation of wiring comes to mind. We will have complete isolation on the emergency side but on the normal side of the LS ATS is fed from the main switchboard, so we will not have isolation.
Also, the downstream LS ATS will always see utility due to the upstream ATS backing up the main switchboard, so it wont ever transfer!

I think this can be done and be compliant but it would be easier to design to avoid this if it new construction. But anytime time I've seen this proposed it is because it is an existing building with a genset and a LS ATS and they now want the whole building to be backed up by installing a larger genset and an ATS on the whole service.
You will have to consider the timing issues of the 2 ATSs so that the optional ATS transfers first but yet be certain you can meet the 10 second rule if the optional switch fails to supply power.

 

[Platinum]

I think this can be done and be compliant but it would be easier to design to avoid this if it new construction. But anytime time I've seen this proposed it is because it is an existing building with a genset and a LS ATS and they now want the whole building to be backed up by installing a larger genset and an ATS on the whole service.

You are exactly right It is an existing building and they are now wanting to back up the entire building.
I wanted to add a service entrance rated Life Safety ATS but it seems that the utility transformer secondary conduit/wire is maxed out.

 

[Platinum]

Anybody else run into this?

 

[steve66]

You are exactly right It is an existing building and they are now wanting to back up the entire building.
I wanted to add a service entrance rated Life Safety ATS but it seems that the utility transformer secondary conduit/wire is maxed out.

Can you get enough lugs on the new ATS to connect the normal side of the LS ATS to the normal side of the new ATS?

That way you don't have 2 ATS's in series, and the LS ATS won't see an outage every time the main ATS does a transfer.