Do we need separate ATS for the critical branch when entire building is fed from the Generator?

[mathan1987]

Hi
I am working on a TI. We are altering an existing Call center building into Cancer treatment center with all the exam room, imaging facilities. There in an existing ATS at the service entrance feeding the Main distribution panel. Do we need to have a separate ATS to feed the critical branch loads?

 

[roger]

I don't know if it's applicable but have you looked at Figure 517.30 No. 2?

Roger

 

[don_resqcapt19]

It is based on the load. See 517.31(B) in the 2020 code.

 

[d0nut]

You would need a second transfer switch in your scenario. You cannot pick up the entire building on a single ATS (which would be an optional standby system) and use it for the essential electrical system in 517. You can certainly pick the whole building up on an ATS, but you would need, depending on load, at least one downstream transfer switch for the essential electrical system.

A better question would be if your cancer treatment center even needs an essential electrical system. Depending on what is happening in the facility, you might not have any Category 1 or Category 2 spaces at all. In that case, no essential electrical system would be required. You would be fine with the single, optional standby transfer switch and an inverter, batteries, or something similar for the emergency egress lighting.

 

[mathan1987]

You would need a second transfer switch in your scenario. You cannot pick up the entire building on a single ATS (which would be an optional standby system) and use it for the essential electrical system in 517. You can certainly pick the whole building up on an ATS, but you would need, depending on load, at least one downstream transfer switch for the essential electrical system.

A better question would be if your cancer treatment center even needs an essential electrical system. Depending on what is happening in the facility, you might not have any Category 1 or Category 2 spaces at all. In that case, no essential electrical system would be required. You would be fine with the single, optional standby transfer switch and an inverter, batteries, or something similar for the emergency egress lighting.

where can i find more information on the category 1 or category 2 space?

 

[d0nut]

Article 517 has definitions and requirements in it, but those are pulling from NFPA 99.

 

[mathan1987]

Article 517 has definitions and requirements in it, but those are pulling from NFPA 99.

thanks for the clarification.