480/277 panel to straight 480 sub panel

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bar714

Member
I've searched forum but haven't found answer I'm looking for. I have a 480/277 panel 3P 4W and a contractor wants to run a straight 480 3P 3W sub panel off it. What are the requirements per the NEC. I believe not running a neutral is ok, but what rating does the sub panel and breakers have to have? Should everything be 480 rated or is 480/277 ok for panel and breakers? Obviously no 277 circuits will be run from sub but I think a 120/208 x-former and 480 single and three phase equipment. I've looked at 240.85, but I dont think that pertains to this. Thanks
 

pete m.

Senior Member
Location
Ohio
I believe not running a neutral is ok, but what rating does the sub panel and breakers have to have?

Not running the neutral to the sub-panel is fine as long as a properly sized EGC is installed or the raceway serves as the EGC. The rating of the sub-panel is determined by the load that is to be served. Further, the sub-panel must be protected within it's ampacity rating.

Should everything be 480 rated or is 480/277 ok for panel and breakers?

Slash rated breakers are fine for this install since you are dealing with a grounded source.

Pete
 

kwired

Electron manager
Location
NE Nebraska
I have always installed the bonding jumper and the neutral bar is now an equipment grounding bar.

Don't give me "what if someone installs a 277 volt load". They are supposed to know better.

Chances are they will attempt to install the 277 volt load to the usual EGC bar if there is no usual neutral bar if they don't know better anyway.
 

Barndog

Senior Member
Location
Spring Creek Pa
I have always installed the bonding jumper and the neutral bar is now an equipment grounding bar.

Don't give me "what if someone installs a 277 volt load". They are supposed to know better.

Chances are they will attempt to install the 277 volt load to the usual EGC bar if there is no usual neutral bar if they don't know better anyway.

Is thats allowed by code. We are installing a 3 phase 480 panel without a neutral and I was thinking on doing the same thing was wondering if there was a code issue with this. Seem to me this would be an acceptable way.
 

kwired

Electron manager
Location
NE Nebraska
Is thats allowed by code. We are installing a 3 phase 480 panel without a neutral and I was thinking on doing the same thing was wondering if there was a code issue with this. Seem to me this would be an acceptable way.

I don't see why not. It is acceptable to land EGC's on that bar if it is used as service equipment. Why wouldn't you be able to put in bonding jumper and use it for EGC's if there is no neutrals to connect to it? Have always done this when there is no need for a neutral and never been questioned about it.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I don't see why not. It is acceptable to land EGC's on that bar if it is used as service equipment. Why wouldn't you be able to put in bonding jumper and use it for EGC's if there is no neutrals to connect to it? Have always done this when there is no need for a neutral and never been questioned about it.

I hate that answer with a passion....but alas, it is the way I have always done it as well.:D
 

kwired

Electron manager
Location
NE Nebraska
I hate that answer with a passion....but alas, it is the way I have always done it as well.:D

Didn't give it much thought when I posted. Generally I don't like that answer either. I guess the better response is to ask where does it say it can't be done? I have found nothing, but have not looked too hard either.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
It is not to uncommon for me to find the arrangement you noted. A fair number of the industrial installations I have seen have limited 277v loads (if any) and the neutral is omitted from many panels.
It is also common to bond the "neutral" bar in those situations and use it as an equipment grounding bar.
I have never thought to question that as a violation but think the only possible violation would be a hazy one if the manufacturer identified it as a neutral bar.
 

kwired

Electron manager
Location
NE Nebraska
I would think again about not pulling a neutral. If you ever want it in the future, you would then have it.

If your intention is to supply motors and transformers the need for a neutral is not that great.

Different story if running 120/240 or 120/208 panel. 120 volt loads are too common and somebody is always wanting a neutral for something there.

There can be times where you maybe intend a panel to not have any neutral load and fill it entirely with line to line loads and have no extra spaces - what is the point of a neutral in this case?
 

Barndog

Senior Member
Location
Spring Creek Pa
I would think again about not pulling a neutral. If you ever want it in the future, you would then have it.

In my case I asked my boss if he wanted a neutral pulled in and he said no. So we did not pull the neutral. I also found the ground bar with the panel so i will install that. Our only load on this panel will be 3 phase battery chargers.
 
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