Feeders length for parallel runs must be within 3% length for both runs of one phase...?

Danny89

Member
Location
Indian Land
I was told to change how I ran my wire for parralel runs of feeders. What's the code requirement for running parralel runs for feeders does the length need to match within 3%?


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winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Code just says they have to be the same length with no specified tolerance. Arguably the 3% spec is looser than what the NEC allows.

The point of parallel feeders is that current divides between the various paths so that you can add the ampacity of the paths. Uneven length means uneven current flow, thus one of the parallel paths could overheat.

-Jon
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Never heard of a percentage, just need to be reasonably close, all must take the same path, an example would be, two in the slab, one overhead would not be compliant. I know one contractor cut all pieces the exact same length, and wadded up the excess 500 mcm in the bottom of the switchgear! LOL!
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
As already stated, they are to be the same length and with that said, the picture does not tell whether they are the same length or not. It's like hillbilly said, they could be wadded up in the other enclosure.

Roger
 

kwired

Electron manager
Location
NE Nebraska
From a theory perspective each conductor of a parallel set should have equal impedance so that current will divide evenly through each conductor of the set. That basically means you should try to attain same characteristics for each conductor of a set including same size, conductor type, length, all run through same raceway/raceway type or other closure or cable assembly type. NEC basically requires same characteristics with little else on details.

3% mentioned is probably a design specification.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
As said above, all of the conductors in each phase must match. There is no need that all phases match.
 

kwired

Electron manager
Location
NE Nebraska
I was told to change how I ran my wire for parralel runs of feeders. What's the code requirement for running parralel runs for feeders does the length need to match within 3%?


Sent from my Moto Z (2) using Tapatalk
Question - is this the supply or is it the feed through lugs with service disconnect (or first disconnect of SDS) at the top end?

I ask because it looks like the EGC's are likely landed on the neutral bus, which would only be acceptable in either situation I mentioned.

Though from past experiences with NQ panels the main breaker would go on this end where the neutral bus is and feed thru lugs would be on the other end. The large lug on the neutral is included when ordering feed thru lugs and is intended for feed thru neutral, but usually isn't there without feed thru kit though you could still order that item and add it anyway.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
Never heard of a percentage, just need to be reasonably close, all must take the same path, an example would be, two in the slab, one overhead would not be compliant. I know one contractor cut all pieces the exact same length, and wadded up the excess 500 mcm in the bottom of the switchgear! LOL!
Don't laugh. That's exactly the way my old boss did it and made us do it.
 

kwired

Electron manager
Location
NE Nebraska
I really wanna see someone take the cover off the LB under the panel.

No, not the big LB (actually, the LL)... the little one behind the connector...........
No problem, take bottom panel off the cabinet - it is attached with screws. If they didn't remove the ones in the back wall before mounting it gets more difficult.
 

480sparky

Senior Member
Location
Iowegia
No problem, take bottom panel off the cabinet - it is attached with screws. If they didn't remove the ones in the back wall before mounting it gets more difficult.
You've got better eyes that I do. I've never seen a cabinet screwed together... just welded.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The EGCs are not on the neutral lugs; they go to the top of the panel.

The words "main lugs" are printed on the bottom of the enclosure.
 
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