Three phase panelboard

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hhsting

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Glen bunie, md, us
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I have sub panelboard A 208/120V, three phase, 225A, four wire fed from 120V, 20A single phase feeder breaker in panelboard B.

Yes that means one phase, one neutral and one equipment ground conductor is bought from panelboard B 20A 120V feeder breaker to sub panel A which is 208/120V three phase.

Weirdest situation I have not seen. Is the above not in code compliance with NEC 2014? Code allow this?
 
Nothing prohibiting it, just a waste of a good panelboard.

Roger
 
Are the conductors feeding the lugs or main breaker of the 3-phase 225A panel within the acceptable wire size range for the panel? The minimum size is probably something like #1 gauge.
 
synchro said:
Are the conductors feeding the lugs or main breaker of the 3-phase 225A panel within the acceptable wire size range for the panel? The minimum size is probably something like #1 gauge.
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Now that I don’t know since they are existing.

The three phase sub panelboard has all 120V single phase 20A breakers and one of the breaker is feeding receptacle in Kitchen the rest maybe or not or may not be even receptacles. However the designer just gave GFCI to feeder breaker feeding the sub panelboard not just branch circuit breaker to Kitchen to GFCI. So they are suppose to change feeder breaker to sub panel to GFCI breaker however feeder cable is existing to remain
 
hhsting said:
Now that I don’t know since they are existing.

The three phase sub panelboard has all 120V single phase 20A breakers and one of the breaker is feeding receptacle in Kitchen the rest maybe or not or may not be even receptacles. However the designer just gave GFCI to feeder breaker feeding the sub panelboard not just branch circuit breaker to Kitchen to GFCI. So they are suppose to change feeder breaker to sub panel to GFCI breaker however feeder cable is existing to remain
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Once again nothing wrong with it.
If the conductors are to small for the lugs a larger conductor can be spliced on to accommodate the lug. Just approve the plans and be done with it

Are you sure the designer doesn't have a typo?


Roger
 
Of course, if someone tries to make an MWBC land on that panel, they're going to be in for a surprise.
 
Is it for computer equipment? One of the restaurant brands we build does this; single 20A 120v feed to the 3P panel with maybe 8-9 120v circuits to POS & printers.


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brantmacga said:
Is it for computer equipment? One of the restaurant brands we build does this; single 20A 120v feed to the 3P panel with maybe 8-9 120v circuits to POS & printers.


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Could be not sure but panel schedule for three phase panelboard shows loads on A, B , C phase how if it’s fed from single pole 120V feeder breaker?

Let’s see ask the designer for sure what is going on.
 
hhsting said:
Could be not sure but panel schedule for three phase panelboard shows loads on A, B , C phase how if it’s fed from single pole 120V feeder breaker?
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The three busbars could be tied together and fed with the one phase.
I think it's still worthwhile to verify it with the designer.
 
hhsting said:
Could be not sure but panel schedule for three phase panelboard shows loads on A, B , C phase how if it’s fed from single pole 120V feeder breaker?

Let’s see ask the designer for sure what is going on.
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So in the type of install I mentioned, we run a single 120v feed into the panel board, and splice the single 120v across all three terminals. Generally all of the restaurants we build want all computer equipment on the same phase.

Some restaurants just have the POS in a panel that has other general receptacles and specify to use the same phase for all POS. Some have a three phase panel, with a three phase feeder, and then specify use a single phase for all. And then some do what you’ve described and have a separate panel with a single phase 120v feeder.


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It sounds like the OP is using a panel as a break-out box to feed a large number of receptacles from a single 20a circuit.

Why not just run one large 20a circuit? Individual breakers aren't going to open before the single breaker feeding it all.
 
LarryFine said:
Why not just run one large 20a circuit? Individual breakers aren't going to open before the single breaker feeding it all.
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If it's feeding different registers like brandtmacga mentioned maybe they want to be able to shut them down individually for service and keep the other ones running.
 
LarryFine said:
It sounds like the OP is using a panel as a break-out box to feed a large number of receptacles from a single 20a circuit.

Why not just run one large 20a circuit? Individual breakers aren't going to open before the single breaker feeding it all.
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They probably figure on disconnecting the loads separately instead of ocp, such as resetting one server or register individually. Probably makes it easier for their tech support to tell the employee to turn off breaker #**, instead of unplugging it at the piece of equipment.
 
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