Where's the Violation?

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charlie b

charlie b

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Existing (old, small) building. Only one panel: 175 amp, 120/208V, 3 phase, circa 1976. Served by outdoor pad-mounted, 112.5 KVA transformer. There is no conductor connected to X3. Hand-written label on panel says 120/208V-1 ph. There are 1-pole breakers in all 42 positions. Panel schedule shows most of them in use, including all three phases.

My best guess is that there is a jumper conductor between two of the phases, so that power can be fed to any breaker on any leg. I don’t know service conductor sizes, so I can’t say whether one leg is carrying too much current. My project will be adding load for HVAC equipment.

I want to tell the owner that the panel has to be replaced. I want to include code citations to forestall any gripes about cost. Other than 110.3B, what can I cite?
 
charlie b said:
Existing (old, small) building. Only one panel: 175 amp, 120/208V, 3 phase, circa 1976. Served by outdoor pad-mounted, 112.5 KVA transformer. There is no conductor connected to X3. Hand-written label on panel says 120/208V-1 ph. There are 1-pole breakers in all 42 positions. Panel schedule shows most of them in use, including all three phases.

My best guess is that there is a jumper conductor between two of the phases, so that power can be fed to any breaker on any leg. I don’t know service conductor sizes, so I can’t say whether one leg is carrying too much current. My project will be adding load for HVAC equipment.

I want to tell the owner that the panel has to be replaced. I want to include code citations to forestall any gripes about cost. Other than 110.3B, what can I cite?
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Did they pull a neutral for every circuit?

JAP>
 
Based on the information on the panel schedule and a photo of the panel as a whole, I infer that all circuits are single pole, with separate neutrals. I did not get a chance to ask an electrician to remove the panel cover. If I go to the site again, I will arrange that.
 
The fact that you have 112.5 KVA transformer feeding this implies that it must be a 3 phase transformer. And the panel is 3 phase. Why in the world would they not have run the 3rd phase conductor? Maybe there was one and it went bad and they just abandoned it since they had no 3 phase load?
As others mention it would be interesting to know the branch circuits neutral setup.
 
The transformer and the panel are definitely constructed with three phase capability. I have no idea why the third phase is not connected. But it appears to have been that way for 40 years.
 
It's odd all together.

Generally a 112.5 KVA Xfmr is used for a 400 amp service.

JAP>
 
There is another nearby building fed from the same transformer. I know nothing about its loading conditions.
 
charlie b said:
There is another nearby building fed from the same transformer. I know nothing about its loading conditions.
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Hopefully that one has a conductor attached to X3 for the 3rd phase doesn't it?

JAP>
 
But if all the details are handled correctly, there's fundamentally no violation using a 3 phase panel for a single phase supply, right?

Cheers, Wayne
 
wwhitney said:
But if all the details are handled correctly, there's fundamentally no violation using a 3 phase panel for a single phase supply, right?
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I think that is right. But the "details" would include blanking off every third breaker slot, to prevent attempts to get power from a de-energized bus bar.

 
I would bet historically it was supplied by single phase and when the other 3 phase building was added POCO simply picked the single phase up on their 3 phase pad
If my thinking is correct the main problem would occur if the 3rd phase is supplied by jumping the line side of the breaker to another phase which cause a severe overload to that phase conductor. On a more minor nature likely a termination problem of lug ratings.
 
charlie b said:
But the "details" would include blanking off every third breaker slot, to prevent attempts to get power from a de-energized bus bar.
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Why would that be required? With a proper splice (no double lugging unless the lug is so listed), what's wrong with feeding two busbars with the same phase? Obviously you'd have to avoid inadvertently sharing a neutral between two circuits that are not an MWBC because they are on the same phase [edit: and you'd need to pay attention to proper OCPD on the feeder conductor feeding two busbars]. Otherwise, I don't see any issue, it would be similar to using a standard 120/240V panel for a 120V only distribution.

Cheers, Wayne
 
wwhitney said:
Why would that be required? With a proper splice (no double lugging unless the lug is so listed), what's wrong with feeding two busbars with the same phase? Obviously you'd have to avoid inadvertently sharing a neutral between two circuits that are not an MWBC because they are on the same phase [edit: and you'd need to pay attention to proper OCPD on the feeder conductor feeding two busbars]. Otherwise, I don't see any issue, it would be similar to using a standard 120/240V panel for a 120V only distribution.

Cheers, Wayne
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Unless the feeder conductor to the double load on the panel is sized for the double load you'd have a problem with an undersized conductor. Plus you'd need an upsized neutral, I'd think.
 
augie47 said:
I would bet historically it was supplied by single phase and when the other 3 phase building was added POCO simply picked the single phase up on their 3 phase pad
If my thinking is correct the main problem would occur if the 3rd phase is supplied by jumping the line side of the breaker to another phase which cause a severe overload to that phase conductor. On a more minor nature likely a termination problem of lug ratings.
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If that were the case the panel in the building in question would have been a 1ph panel to begin with, not 3ph.

It would make more sense if the services were 3ph to begin with and the 3rd phase petered out on the transformer somehow and they had to jumper in the panels.

Although I cant see how that could ever be either.

JAP>
 
gadfly56 said:
Unless the feeder conductor to the double load on the panel is sized for the double load you'd have a problem with an undersized conductor.
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Hence my parenthetical comment on the OCPD.

Seems to me the simplest way to feed the other busbar would be to use a properly sized conductor from a single pole breaker on one of the phases present in the feeder to supply the main lug/main breaker lug for the missing phase.

Cheers, Wayne
 
wwhitney said:
Hence my parenthetical comment on the OCPD.

Seems to me the simplest way to feed the other busbar would be to use a properly sized conductor from a single pole breaker on one of the feeder phases to the main lug/main breaker lug for the missing phase.

Cheers, Wayne
Click to expand...

Maybe I misunderstand, but how does that protect the feeder from the transformer to the panel?
 
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