Where's the Violation?

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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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I agree there is no explicit violation. One could argue manufacturers instructions.
 
gadfly56 said:
Maybe I misunderstand, but how does that protect the feeder from the transformer to the panel?
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Say the feeder is on phases A and B, the feeder lands on 2 of 3 lugs of the main breaker, and the main breaker size properly protects the feeder conductors. Install a single pole breaker on phase A or B, and run a conductor of sufficiently large size to be protected by that single pole breaker from the single pole breaker to the phase C lugs of the main breaker.

Cheers, Wayne
 
jap said:
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>
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True. I didn't think about a 3ph panel would not have been usedc:thumbsup:

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 phases present in the feeder to supply the main lug/main breaker lug for the missing phase.

Cheers, Wayne
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That would certainly work and not result in an overloaded service conductor. The only limitation I can think of is I believe a 50 amp SP breaker is the largest available.
 
augie47 said:
The only limitation I can think of is I believe a 50 amp SP breaker is the largest available.
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That might be fine, as you'd need to avoid overloading the leg feeding two busbars anyway. But you could always use just one pole on a double pole breaker.

Cheers, Wayne
 
It could have been a high leg delta, but the current occupants only have 120 V loads, so they somehow (hopefully legally) put a jumper between two of the bus bars. That way they avoid the high leg and get a third more slots to use.
 
gadfly56 said:
I have a crazy idea: re-pull with all three conductors.
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That is exactly what I plan to do. I will advise the contractor (it's a design/build project and I am not the engineer of record, so I have no command authority) to do the following:
  • Disconnect and remove the existing service conductors and conduit.
  • Run a new set of service conductors in a new conduit, this time including all three phases, the neutral, and the supply side bonding jumper.
  • Replace the existing panel with a new, 120/208 volt, three phase, 225 amp panel.

It seems that the only direct answer to the specific question I asked is the 110.3(B) that I cited already. If that is all there is, I will consider it enough.

Many thanks for all the contributions.
 
I would pull the panel cover and look at the main lug wiring, rather than speculate. It's possible it's a 1ph panel as often used in a 3ph-supplied apartment building. It's also possible the panel was built (or rebuilt) with all stabs bolted to only two buses.
 
Barbqranch said:
It could have been a high leg delta, but the current occupants only have 120 V loads, so they somehow (hopefully legally) put a jumper between two of the bus bars. That way they avoid the high leg and get a third more slots to use.
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That's not possible because there is no wild leg in this panel.
How do we know this?
Because we already know there's only 2 phases coming into the existing 3 phase panel from the transformer.
How do we know one of them is not the wild leg?
Because the panel is full of 1p 20's and they would have already burned up half or more of anything coming off of this panel because it's full of 1p 20's.

Plus,

If you put a jumper between 2 bussbars where 240v delta actually did exist, the panel would have had a nice smokey smell and most of the parts would have been blown out of it from a direct phase to phase fault.

Jap>
 
LarryFine said:
I would pull the panel cover and look at the main lug wiring, rather than speculate. It's possible it's a 1ph panel as often used in a 3ph-supplied apartment building. It's also possible the panel was built (or rebuilt) with all stabs bolted to only two buses.
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I agree.

We need to know if the panel itself is actually 1ph or 3ph.
The 1ph tap on the transformer is easier to explain than using a 3ph panel for a 1ph service.

JAP>
 
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?

Cheers, Wayne
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If all three legs are used, I'm not seeing how the jumper wire between say legs B and C would be installed compliantly, and you'd probably wind up with an odd load distribution to not overload one of the hot feeds from the transformer, like 200A on leg A (feeding "A" phase) and 100A ea on Leg B, which is feeding 2x as many breakers on phases "B" and "C".
 
wwhitney said:
Are the instructions really going to say that that voltage between any two of the busbars has to be positive? Surely the instructions are just going to put an upper bound on that voltage, not a lower bound.

Cheers, Wayne
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Many times loadcenter type panelboards have a schematic of the lines and and the busbars. Depending on what exactly it shows.......

BTW I'm not necessarily on the side of it goes against the instructions. Was just throwing it out as a possible. I actually think most 110.3(B) calls are based on something that isn't specifically disallowed.
 
charlie b said:
That is exactly what I plan to do. I will advise the contractor (it's a design/build project and I am not the engineer of record, so I have no command authority) :
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Bit of your old Navy days slipping in there, Charlie? Not really a term we civies hear a lot.:)

IIRC, LCDR (Ret), USN.

Division leader of gennys on a carrier? Or something about two ships? Cannot recall.
 
charlie b said:

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.
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The other possibility is that the tabs that connect the breakers to the buss have been re-arranged, so none of the breakers are actually connected to the 3rd buss.

I ran across my first panel like this on a high leg service, and it took a while to figure out what was going on.

Going down one side, the breakers were phased ABC, ABC, ABC, then at about the 15 space it changed to AB, AB, AB.....

I'm still not sure if that was a field modification, or a custom ordered panel.
 
jumper said:
(Referring to "command authority") Bit of your old Navy days slipping in there, Charlie? Not really a term we civies hear a lot.
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It surrounds me now. I recently started a new job with the US Army Corps of Engineers.
jumper said:
IIRC, LCDR (Ret), USN. Division leader of gennys on a carrier? Or something about two ships? Cannot recall.
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If you are talking about me, it would be CDR (Ret) USNR, having served as electrical division officer and electrical officer on two carriers and one cruiser.
 
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