1PH Main CB on 3PH panel

[designer82]

is this possible, can it be done?

installing a 1PH Main CB on 3PH panel that is....................................................

 

[don_resqcapt19]

Sure as long as you only have two ungrounded conductors and are planning on only using single phase loads.

 

[tom baker]

You will need a main breaker retaining kit. How will you feed the other 2 phases?

 

[GoldDigger]

You will need a main breaker retaining kit. How will you feed the other 2 phases?

I suspect that OP is referring to a two pole single phase main breaker designed for a split phase panel.
Would that breaker fit into the main breaker position of a three phase panel?
It is possible, but not definite, that OP is thinking of using a backfed branch breaker, in which case it might be a single pole breaker. leaving the other two hot buses disconnected. Or adding a jumper?

 

[designer82]

Thanks for your replies.

I was asking because it's an existing 3 phase panel (confirmed by Square D) but has only 2 pole breakers on it and the main breaker kind of looked like 1 phase to me (2 pole). However the front cover was not removed and most of this main breaker is covered.
Not really sure why I even got this idea.

I'm now sure it is an actual 3 phase breaker/ 3 phase service.

Thanks

 

[kwired]

Thanks for your replies.

I was asking because it's an existing 3 phase panel (confirmed by Square D) but has only 2 pole breakers on it and the main breaker kind of looked like 1 phase to me (2 pole). However the front cover was not removed and most of this main breaker is covered.
Not really sure why I even got this idea.

I'm now sure it is an actual 3 phase breaker/ 3 phase service.

Thanks

If it is a NQ panelboard with QBL main breaker (125-225A) you can't tell the difference between single and three phase mains when the cover is on. Either one fits the same assembly and just depends on if you had single or three phase bus as to which one you use.

The Newer QO "loadcenters" (newer is like the last 30 or so years now) use the QOM series mains in single phase panels and a QBL or similar style in the 125-225 amp versions or a back fed main with hold down for 100 amp and less. Those definitely are different looking even with cover on compared to the NQ panelboards.

 

[designer82]

If it is a NQ panelboard with QBL main breaker (125-225A) you can't tell the difference between single and three phase mains when the cover is on. Either one fits the same assembly and just depends on if you had single or three phase bus as to which one you use.

The Newer QO "loadcenters" (newer is like the last 30 or so years now) use the QOM series mains in single phase panels and a QBL or similar style in the 125-225 amp versions or a back fed main with hold down for 100 amp and less. Those definitely are different looking even with cover on compared to the NQ panelboards.

Thanks. Here is some pics. Not sure if you can tell..

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[kwired]

Thanks. Here is some pics. Not sure if you can tell..

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Image 1 hosted in ImgBB

ibb.co

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Image 2 hosted in ImgBB

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Image 3 hosted in ImgBB

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That is older loadcenter from before they started using the QOM mains for single phase panels.

Main breaker is a Q2 series which today the same series is now called QBL series. Doesn't matter if it is single or three phase all that shows with cover on is the handle and is same handle on two or three pole breakers so you going to have to remove cover to know for certain which it is.

newer versions pictured below, three pole is basically the same thing as the two pole but with the right pole left out. Will bolt on to same equipment as the three pole and handle still in same position.

 

[gar]

210928-2007 EDT

When you look at the main panel and see 2 pole breakers, and 1 pole breakers, located side by side and there are no gaps between them, then you almost certainly have a single phase panel. If it were a 3 phase panel used in a single phase application, then you would see every third breaker location empty. A single phase panel has two hot bus bars, and breakers are located as you see in the photo.

A single phase panel can be supplied from 2 hot phase lines and the neutral.

.

 

[kwired]

210928-2007 EDT

When you look at the main panel and see 2 pole breakers, and 1 pole breakers, located side by side and there are no gaps between them, then you almost certainly have a single phase panel. If it were a 3 phase panel used in a single phase application, then you would see every third breaker location empty. A single phase panel has two hot bus bars, and breakers are located as you see in the photo.

A single phase panel can be supplied from 2 hot phase lines and the neutral.

.

Could be three phase supply three phase panel and on 208/120 and have every position filled but no three pole breakers at all.

The particular series of main breaker OP has you can only view the handle of the main when the cover is on, and both the two and three pole versions of this series have identical handles. You must remove cover to verify unless there is other factors to indicate some possibilities. Three ungrounded and one grounded on the service drop could raise possibility there is three phase in there without ever opening anything to look. If only two ungrounded and one grounded then almost has to be single phase, that is if you have overhead drop and can see what is coming in. Unground may not be as easy to determine.

 

[gar]

210928-2101 EDT

kwired:

You are correct that it could be a 3 phase Y. In this case one can measure several outlets, and check for 208 vs 240.

.

 

[Little Bill]

That is older loadcenter from before they started using the QOM mains for single phase panels.

Main breaker is a Q2 series which today the same series is now called QBL series. Doesn't matter if it is single or three phase all that shows with cover on is the handle and is same handle on two or three pole breakers so you going to have to remove cover to know for certain which it is.

newer versions pictured below, three pole is basically the same thing as the two pole but with the right pole left out. Will bolt on to same equipment as the three pole and handle still in same position.

View attachment 2557935View attachment 2557936

Aren't those I-Line breakers?

Never mind, I see they are line/load breakers not load lug only.

 

[kwired]

Aren't those I-Line breakers?

Never mind, I see they are line/load breakers not load lug only.

QBL series is also an I line option if fitted with bus plug instead of lugs on one end. That is a factory option though, most other termination options are field convertible.