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

[Danny89]

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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[ptonsparky]

Where did you come up with 3%?

 

[480sparky]

Probably someone quoting a job spec they ran across.

 

[ptonsparky]

Probably someone quoting a job spec they ran across.

At least that may be attainable.

 

[winnie]

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]

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]

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

 

[hillbilly1]

And it’s each phase that needs to be the relatively same length, not all phases exactly the same as the others.

 

[kwired]

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.

 

[zbang]

I was told to change how I ran my wire for parralel runs of feeders.

Were they complaining about the length or the path? Sounds like the length because you asked, but....? Unless they don't like the almost-trivial difference in the white, it looks fine to me. (How long are those feeders, overall?)

 

[LarryFine]

As said above, all of the conductors in each phase must match. There is no need that all phases match.

 

[sameguy]

Looks fine to me

 

[kwired]

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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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]

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.

 

[480sparky]

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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...........

 

[kwired]

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.

 

[ptonsparky]

I remember taking the amp readings on a larger service after the POCO had trimmed up their ends to make connections at the pole top transformers. Noticeable difference but it sure wasn‘t going to cause a melt down.

 

[480sparky]

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.

 

[kwired]

You've got better eyes that I do. I've never seen a cabinet screwed together... just welded.

I didn't see it in that photo, but do know Square D cabinets like that one have the end panels screwed on.

 

[LarryFine]

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.