Parallelling Conductors

[necnotevenclose]

Reading through NEC 310.4(1) it states that the conductors shall be the same length. This makes sense to me in a straight run, but if you have to make any bends or turns it seems to me that in a horizontal run the inside feeder and the further most outside feeder would not be the same lengths. My question is how can I meet this code requirement?

 

[iwire]

My question is how can I meet this code requirement?

You can't meet the requirement, the conductors will never be the same length. You can try to get them as close as possible to the same length.

 

[qcroanoke]

Usually when we pull the conductors off the spool we make sure to get them all the same length per phase and mark them for their phase right then.
And whatever we cut off of one conductor when terminating we cut that same amount off of the rest in that phase. Sometimes it looks horrible but
this is a situation where neatness doesn't always count.That's the way it is. I don't think you can get any closer than that.

 

[hardworkingstiff]

Your point is a good one. It shows the installer must be thinking and planning when roughing in the conduit.

 

[necnotevenclose]

Thanks for the replies guys. Just so I'm understanding this correctly let me give a for instance:

If I'm planning on running (4) runs of 600kcmil and the most inner feeder is 200' and the most outer feeder is say 205' then with allowing for an additional 10' of feeder to terminate I might be looking at providing (4) runs of feeder that are at least 215'. Is that correct? If there was any extra cable where would that be stored at? Would it be in the transformer vault?

 

[iwire]

You would store it wherever you can find room.

Better if you can re-think your conduit run, perhaps in a square configuration instead of flat or a different route with opposing bends.

The longer the total length the less critical the individual lengths become. Which is good because your not going to lay out four 200' sets of 600 CU on the floor to compare lengths.....at least I would not.

 

[hardworkingstiff]

The longer the total length the less critical the individual lengths become. Which is good because your not going to lay out four 200' sets of 600 CU on the floor to compare lengths.....at least I would not.

I wouldn't either, but I would pull a measuring tape in each conduit and write down the length of the conduit run. Then I would try to leave enough "extra" wire in the panel or transformer to make the conductors equal in length (or at least as close as I can get them).

 

[bkludecke]

The engineers that I've worked with have been OK with +/- 1% on the lengths as being essentially the same length. Like already stated, no-one really checks on this (other that the plaintiff's experts).:grin:

 

[don_resqcapt19]

Assuming a 1600 amp circuit and runs of 210, 215, 220 and 225 feet the current distribution would be 414A on the 210', 405 amps on the 215', 385 amps on the 220' and 386 amps on the 225'. I would have no problem with those lengths for this circuit as the 600 kcmil is rated at 420 amps and this is not exceeded even with a 15' difference between the shortest and longest. Note, as Bob said, there is no code allowance for any difference in length between the conductors, but this is impossible to comply with.
Don

 

[jrannis]

Reading through NEC 310.4(1) it states that the conductors shall be the same length. This makes sense to me in a straight run, but if you have to make any bends or turns it seems to me that in a horizontal run the inside feeder and the further most outside feeder would not be the same lengths. My question is how can I meet this code requirement?

You should do the best you can. I wouldnt consider trying to hide an extra 5 or 10 feet of 600MCM. I have never been called out on 310.4(1). If it wasnt in the NEC you would see conductors coming from three different directions, and random lengths.

 

[infinity]

You should do the best you can. I wouldnt consider trying to hide an extra 5 or 10 feet of 600MCM..

I agree. As long as all of the conduits are run together I wouldn't be concerned with the conductor length.