3 Phase Main Panel, 1 Phase Transfer Switch/Sub Panel


Old 02-22-16, 07:12 AM
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Join Date: Nov 2015
Posts: 914
3 Phase Main Panel, 1 Phase Transfer Switch/Sub Panel

Is it possible to move over some circuits from 3 Phase circuit to Single split phase sub panel?

The reason I'm asking is few years back at the work my boss wanted to have ability to hook up portable generator and power essential devices (phone system, server, and few computers, and some lights) during power outage.
The generator was single phase as most are. However, the building was getting 3 phase.

Only way I can think of was move essential circuits from main 3 phase circuit over to single phase transfer switch or sub panel and transfer switch combination. Then, use just 2 phases from 3 phase to feed this transfer switch.
So, the single phase panel will get 208V during normal operation and 240V on generator. But, all of the essential circuits are 120V anyway and there are no circuit requiring 3 phase.

As far as I know it will work. However, I could never find if it was allowed and safe back then. So never done.

Is this possible?
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Old 02-22-16, 09:12 AM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
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Yes that is allowed. It's very common in buildings with 3 phase service to run single phase 208Y120V panels to the office area. I don't see any reason why one of those panels couldn't have a transfer switch or interlock on it.
Old 02-22-16, 04:29 PM
Thread Starter
Join Date: Nov 2015
Posts: 914
Good to know. Haven't really touched 3 phase circuit before, so I didn't know it was very common.

Now I know what to do when same question arise.

Old 02-22-16, 04:42 PM
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Join Date: Jan 2010
Location: USA
Posts: 9,385
It should work fine, but be wary of any multiwire branch circuits you may find, they need special treatment. If you have any 3 circuit multwire branch circuits, they cannot be transferred to a single phase panel.

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