Existing Delta Service?

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Npstewart

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Hello, working on a renovation and cant figure out if this is a delta service. The panel is marked as a delta, the electronic meter says 240 on it, its definitley 3-phase, the MDP has all 3-phase breakers in it, but the panel attached is filled with single pole circuit breakers. Does this make sense? Ill see if I can post a picture of the service mast.
 

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Service Mast.

Service is 600A, looks to be a parallel drop, one of the phase conductors looks much smaller then the other 2.
 

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The smaller phase is probably the high leg running limited 3 phase loads. I also see single pole breakers on the B slot?
 
Ok just figured it out.. Look at the top of the panel, it says "A" & "B". Somehow they installed a 3 phase panel and only connected phase A&B. Something illegal is going on here im sure.. They must have either phase "A" or "B" connected to two of the phases.
 

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Npstewart said:
Ok just figured it out.. Look at the top of the panel, it says "A" & "B". Somehow they installed a 3 phase panel and only connected phase A&B. Something illegal is going on here im sure.. They must have either phase "A" or "B" connected to two of the phases.
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Perhaps, but that wouldn't correlate with A left, B right.
 
The panel in the OP has movable 'breaker fingers'. It would be possible to reconfigure the branch panel so that all available spaces are 1-phase. The name tag on the panel lists the 'maximum' voltage it can be used on.

You need to remove the interior deadfront and look at the incoming cables and actual finger locations.
 
jim dungar said:
The panel in the OP has movable 'breaker fingers'. It would be possible to reconfigure the branch panel so that all available spaces are 1-phase. The name tag on the panel lists the 'maximum' voltage it can be used on.

You need to remove the interior deadfront and look at the incoming cables and actual finger locations.
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Still wouldn't correlate with A left, B right, at least not phasing. The fingers from outside buses extend across to cover both left and right spaces.

And what about listing if there is a phase-to-space diagram???
 
Smart $ said:
Still wouldn't correlate with A left, B right, at least not phasing. The fingers from outside buses extend across to cover both left and right spaces.
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Yes, the breakers, across from each other share a common finger, but so what. The A-Left and B-Right may have been describing the incoming lug arrangement. At the time and location of the original installation, it may have been acceptable to have C-Phase as the high leg as shown on the nameplate.

But most likely the A and B have simply to do with either left side or right side columns of breakers. They were probably put there by someone who had no intention of linking them to the wiring.

And what about listing if there is a phase-to-space diagram???
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The OP should post the diagram, but I'll bet it is generic.

Everything will be a guess, until the deadfront is removed.
 
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Picture of the supply transformer as well as picture of panel with deadfront removed would have been more helpful.

Panel could have been modified - as said this age of a QO panel had removable "fingers" on the bus and would be possible.

Service could also have been converted from 240/120 delta to 208/120 wye at some point in time as well.

It could even be a single phase panel, though the label says it is three phase. May not be original cover for some reason.
 
kwired said:
Note the label that says the C phase is the high leg.

When did NEC start requiring high leg to be B phase?
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A long time ago? Can't name the year but I would say at least 20 years ago.
I know some utilities won't allow it on B phase.
 
qcroanoke said:
A long time ago? Can't name the year but I would say at least 20 years ago.
I know some utilities won't allow it on B phase.
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The panel in the OP is a type NQOB. Square D stopped making these around 1985, when they introduced their NQOD panel.

Utility metering standards almost always require the High Leg to be connected at the C-Phase location of the meter socket. Other than that, utilities don't typically care about 'phase positions' inside of service entrance equipment.
 
qcroanoke said:
A long time ago? Can't name the year but I would say at least 20 years ago.
I know some utilities won't allow it on B phase.
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I've been in the trade about 27 years and high leg was required to be the center bus when I was first starting in the trade, was using 1987 NEC when I started.
 
jim dungar said:
The panel in the OP is a type NQOB. Square D stopped making these around 1985, when they introduced their NQOD panel.

Utility metering standards almost always require the High Leg to be connected at the C-Phase location of the meter socket. Other than that, utilities don't typically care about 'phase positions' inside of service entrance equipment.
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I remember , early 80's , High Leg came in on C phase and was moved to B phase after . South East .



Don
 
Loads?

Loads?

Just curious if you have researched the connected loads? Could the original installer have used two 1P breakers to server a single plase or three breakers to serve three phase loads with no handle ties installed? Not saying this is correct of code compliant but could be how it was installed??
 
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