Combining phase conductors in parallel sets

Chris3585

Member
Location
Smyrna, Georgia
I am working on a project with multiple 4000 amp, 480 volt electrical services. The contractor has proposed grouping the phase conductors for the parallel sets to make installation easier and also to reduce the stress on the lugs.

Is it acceptable to group the phase conductors? I think that this type of installation would be in possible violation with NEC 300.20(B) since the exterior pad mounted transformer can not be vented. The contractors disagrees and says that we would not be in violation because we will not be passing through any form of hole or cut-out in ferrous metal resulting in unwanted heating of the surrounding metal (as there is not bottom in either the transformer or switchgear).

Does anyone else have an opinion on this?

Thank you,

Chris IMG_1024.jpg
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
It can be done based on 300.20(B) when you have an open bottom switch or MCC. I think Iwire has some pics of this type install.
 

kwired

Electron manager
Location
NE Nebraska
Read the exception to 300.3(B)(1), it permits this installation.

Add: 300.20 can complicate it but it can be dealt with by cutting slots if entering an enclosure with a ferrous bottom.
 
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iwire

Moderator
Staff member
Location
Massachusetts
I do have pictures somewhere, I will see if I can find them.

I have personally done it with two different 3000 amp services. It does make things easier at the switchgear.

One thing I would like to point out is that the job may have been engineered assuming only 3 current carrying conductors in each raceway (neutral not counted as a current carrying conductor) and doing it the way the EC proposes is four current carrying conductors per raceway possible causing a ampacity rating violation.
 

kwired

Electron manager
Location
NE Nebraska
One thing I would like to point out is that the job may have been engineered assuming only 3 current carrying conductors in each raceway (neutral not counted as a current carrying conductor) and doing it the way the EC proposes is four current carrying conductors per raceway possible causing a ampacity rating violation.
Good point - that is something that could be easily overlooked.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector
If it's a utility transformer, you might run it by them. For some reason (an attempt was made to explain it to me, but it was wayyyyy over my head), the local utilities will not allow such.
 

kwired

Electron manager
Location
NE Nebraska
If it's a utility transformer, you might run it by them. For some reason (an attempt was made to explain it to me, but it was wayyyyy over my head), the local utilities will not allow such.
Sounds more like an attempt to baffle you with BS in hopes you give up and do it the way they want you to do it:happyyes:
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Here is a picture a friend of mine took and I posted a few years ago.

Seems like you'd have to be sure there were no metal bends or fittings in the conduit runs. On the service side, utilities sometimes require metal bends to minimize the likelihood of conduit damage on long pulls of large wire.
 

kwired

Electron manager
Location
NE Nebraska
Seems like you'd have to be sure there were no metal bends or fittings in the conduit runs. On the service side, utilities sometimes require metal bends to minimize the likelihood of conduit damage on long pulls of large wire.
That is true, and usually would be more of an issue if you are installing it for them then if it is considered customer's equipment. In many cases such conductors and raceways are considered on the customer side of the service point and POCO has little or no say in what gets installed beyond the service point. The part that enters their transformer or metering cabinet is about all they will have a say on.
 
Are we missing something here?

Are we missing something here?

Are we missing something here?

Doesen't a grounding conductor need to be in the conduits with the current carrying conductors?
You know, just in case there is a nick, a cut or ground hog should happen to occur in the wiring.:blink: "The ground wire makes the breaker trip"

I have always installed a complete set of wires in each feeder conduit.
Normally, The AHJ requires it.
 

jap

Senior Member
To me, The larger bar is the Neutral bar and the smaller bar at the bottom down low would be the Equipment Groud bar so I'd say technically the smaller wires phased Grey and landed on the larger bar are in fact Neutral Conductors.
 

jap

Senior Member
Are we missing something here?

Doesen't a grounding conductor need to be in the conduits with the current carrying conductors?
You know, just in case there is a nick, a cut or ground hog should happen to occur in the wiring.:blink: "The ground wire makes the breaker trip"

I have always installed a complete set of wires in each feeder conduit.
Normally, The AHJ requires it.
If a wire gets nicked or cut inside a PVC Conduit, having an equipment grounding conductor run along with them with do nothing to clear a fault.
 
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