ECN Forum Forums General Topics of the Trade General Discussion Area using a 3 phase panel on a single phase system?

In interesting subject came up today.

If a fellow has a 3 phase panel, and wants to use it in his house. Could he?

The idea was to take the one phase and pick up 2 lugs, and leave the remaining phase for the third lug.

I suggested to go with single phase panel, but Im wondering if this method would be ok as well?


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I've seen it done several times but I wouldn't recommend it it

I have a 3 phase panel in my shop, using it on single phase power. Just one I had lying around when I built the shop. I only have about 5 circuits in it, so I just hooked up the a and c phases. It looks like a 3 phase high leg panel, with a blank plate in every third space. That being said I would not put a 3 phase panel in a house, just not enough breaker spaces, or if you pick up 2 phases on on leg you could be way unbalanced, not really a good idea.

Code wise...110.3 (B) on the red tag. That's IF there was a permit!

Along the same track, I came upon a single phase panel, om a three phase feeder and three phase loads. The genius used the isolated neutral bar for the 'c' leg!!!

It's tempting ... but technicall a no-no.

The panle lable lists the distribution systems that the panel is listed for - and yours won't make any reference to any single-phase system. Thus, the 'listing and labeling' violation.

Plus, of course, there's the usual doubled wires under one lug.

"But we'll be careful!" folks always say. I guess that most of the time they are. Good heavens, though ... panels are not that expensive!

It's a loser...

Get the right stuff.

I agree with the other Members - do not use the 3 Phase Panelboard on a Single Phase 3 Wire System.
Beside the Listing Issues & Code Issues, it is really sloppy; especially where Multiwire Circuitry &/or 2 Pole L-L Circuitry is used.

Going the opposite way - using a Single Phase 3 Wire Panelboard on a Three Phase System, has a few possible applications, which include:

Example 1:
120/240V 1 Phase 3 Wire Panelboard on 240/120V 3 Phase 4 Wire Delta System; connecting Lines A & C + Common Neutral to 1 Ph. Panelboard.
This has been done where 1 Phase loads are needed only.
No Wild Phase (Hi Voltage to Ground Phase) issues in the Panelboard.

Example 2:
120/240V 1 Phase 3 Wire Panelboard(s) on 208Y/120V 3 Phase 4 Wire Wye System; connect (2) Ungrounded Feeders + Star Point (Neutral) to Panelboard.
This is somewhat sloppy (IMO) for Commercial / Industrial stuff, however is very common in Multi-Family Dwellings, per a "Network" Service design.

Example 3:
120/240V 1 Phase 3 Wire Panelboard(s) on 240V Corner Grounded Delta System; connect the (2) Ungrounded Conductors - Phases / Lines A & C to the Bus Kit, then connect the Grounded Conductor - Phase / Line "B", to the Isolated Neutral kit.
Line "B" is used as a Common, where (2) 1 Phase 2 Wire loads are connected, as described in the following Illustration:



Refer to Corner Grounded 3 Phase 3 Wire Delta, at the Tech. reference section for more information.

Forgot to add...

The latter example (Example #3) would require 1 Pole devices with a Single Pole AIC rating at no less than 240V.

Furthermore, the Panelboard must be Listed for such use.

Also, this setup _SHOULD NOT_ be used where the Neutral Kit is connected to an Ungrounded Conductor.

This setup was common "Back In The Old Days" (installed up to circa 1980), and may still be found existing in "Older" Industrial areas.


-- Scott

Great description Scott, as usual.

I haven't had any experience with that apartment house system but I have heard a lot about it. Usually people wondering why their heating appliances don't work right.

The others I have seen a lot of. The corner delta is common on those pumping stations you see along the road (all 3p L/L load). We also have a lot of red leg here, in light industrial bay areas and they usually have a 3p panel in the shops and a 1p panel for the house loads and offices.

I have also come across 3 phase panels on ungrounded single phase systems where the center bus was the neutral and since it was not grounded, it had to have OCPD's and yes the breakers were rated for switching the neutral

I have seen one installed in a firehouse with 2 lugs on 1 phase. That made 30 breakers on 1 leg and 15 on the other. The panel was very unbalanced. That panel is still in operation today, I believe. Not a good installation, I doubt it was ever inspected.