I've seen this topic discussed before but have a slightly different question. If I have a system less than 150kva, I can use a single transfer switch. My question is can I then have a single panelboard? If life safety must remain separated on a separate panelboard, I don't see how I could effectively do this without maintaining separate transfer switches.
NEC 517.40 150 kva or less essential electrical system
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In my opinion, even with a single transfer switch, you still need separate systems for the life safety branch, and critical branch.
The reason I believe that is that the code still requires separation of those systems. (The exception you quoted only allows a single ATS to be used - it doesn't say anything else about combining any of the rest of the systems. Unless its changed since the last time I looked at it.) And that required separation can only be acheived with separate panelboards.
You could run 2 sets of wire from the ATS - one to the critical panel, and one to the Life safety panel. Each set in a separate conduit.
The reason I believe that is that the code still requires separation of those systems. (The exception you quoted only allows a single ATS to be used - it doesn't say anything else about combining any of the rest of the systems. Unless its changed since the last time I looked at it.) And that required separation can only be acheived with separate panelboards.
You could run 2 sets of wire from the ATS - one to the critical panel, and one to the Life safety panel. Each set in a separate conduit.
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