3 Phases panel at 1 phase

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Harry Alonso

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Hi, we have a old 3 phases panelboard that the owner wanted to run off; we are expanding a bulding and need a subpanel but we need 120v/240v, by 110.3(A) FPN this (3PH) isn't identified as suitable for this specific purpose. My supervisor who's hold the journeyman licence says that we can use this panel. How safe and legal will be do this change? It is any othe article that prohibit this kind of changes? Thanks for your help.
 
This shouldn't be a problem, as long as a few things are observed:

If this is an "old 3-phase" panel, it may be supplied by a Delta system. If so, is there a system neutral? If so, you must avoid the high leg. If no neutral, you cannot get 120v.

If this is a Y system, the voltage between phases will be 208, and not 240. Any 240v or 240/120v equipment must be suitable to run on 208v.

You must calculate that the existing and new loads combined are within the rating of everything in the existing service, all the way back to the utility tranformers.
 
The way I read your message is you want to use an old 3-phase panel in a building served with only single phase?

If that is the case, then it should be no problem. Just ignore the center bus, and don't try to originate any circuits from those bus bar connections. :grin:

I liken this as the same thing as using a 3-pole disconnect switch on a 2-pole load. I see that all the time. :wink:
 
kbsparky said:
The way I read your message is you want to use an old 3-phase panel in a building served with only single phase?

If that is the case, then it should be no problem. Just ignore the center bus, and don't try to originate any circuits from those bus bar connections. :grin:

I liken this as the same thing as using a 3-pole disconnect switch on a 2-pole load. I see that all the time. :wink:
Click to expand...

I didn't read it that way, I thought he was trying to feed a single phase panel from a three phase one. I am surprised that a 3 phase panel in a single phase system would be OK.

I just redesigned a service where someone had wired a three phase panel in a single phase system by taking Phase A to two of the three busses and Phase B to the third bus. Needless to say it was a mess.

Jim T
 
Harry Alonso said:
Hi, we have a old 3 phases panelboard that the owner wanted to run off; we are expanding a bulding and need a subpanel but we need 120v/240v, by 110.3(A) FPN this (3PH) isn't identified as suitable for this specific purpose. My supervisor who's hold the journeyman licence says that we can use this panel. How safe and legal will be do this change? It is any othe article that prohibit this kind of changes? Thanks for your help.
Click to expand...

If you can get 120v/240 from this panel to branch circuits then why would this be a problem to sub feed a panel. You may have to watch for unbalanced loads etc. but it is legal.
 
LarryFine said:
"How does it feel?"

Tomorrow is the birthday of the user of my avatar.
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Happy Birthday Larry Fine and Bobby D.
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AN UNCANNY RESEMBLANCE--- ESP. THE HAIR​
 
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