Parallel Conductors

[millers520]

In reguards to parallel conductors in the same conduit, how critical is it to have all of the conductors the same length. I know that overheating can result but can they be several inches longer than each other? In other words, how exact must they be? Also, the same rule for the neutral and ground in the same conduit?

 

[electricalperson]

in my experience a foot does not matter very much. one conductor might carry a few amps more than the other. try to keep them as exact as possible.

 

[electricalperson]

if they are in the same conduit you should have no problem keeping everything the same length.

 

[raider1]

A few inches difference will most likely not be a issue.

Chris

 

[iwire]

In reguards to parallel conductors in the same conduit, how critical is it to have all of the conductors the same length. I know that overheating can result but can they be several inches longer than each other? In other words, how exact must they be? Also, the same rule for the neutral and ground in the same conduit?

Each conductor of the same phase or neutral must be the same lenght but each group can be different lengths.

'A' phase could be 10', 'B' 12', 'C' 14' and neutral 20'.

 

[G._S._Ohm]

My take on this follows:

Ohms per foot for 4/0 = 49 uohms and for 3/0, 62 uohms.
The worst case tolerance would be for only two paralleled conductors.

If you needed a value halfway between these two, that is 56 uohms, it would be manufactured by someone.
Probably it's not.

56 is about 13% away from either 49 or 62.

Therefore, +/- 13% is a reasonably close tolerance to follow for length, until somebody can find an NEC table or statement that seems to dictate the need for a closer tolerance.

 

[iwire]

My take on this follows:

Ohms per foot for 4/0 = 49 uohms and for 3/0, 62 uohms.
The worst case tolerance would be for only two paralleled conductors.

If you needed a value halfway between these two, that is 56 uohms, it would be manufactured by someone.
Probably it's not.

56 is about 13% away from either 49 or 62.

I have to be honest, I have no idea what the above means. :grin:

Therefore, +/- 13% is a reasonably close tolerance to follow for length, until somebody can find an NEC table or statement that seems to dictate the need for a closer tolerance.

In my opinion the NECs choice of wording is poor. The NEC tells us parallel conductors 'shall be the same length' they do not give a tolerance.

In the real world they will be different lengths and sometimes by quite a bit. If that matters or not greatly depends on how oversized the conductors are in relation to the over current protection rating is.

For example I ran 5 sets of conductors for a 1600 amp feeder but the total ampacity of the 5 sets was well over 2200 amps so if one of the conductors was taking more of the load the conductor would still not be overloaded.

 

[Dennis Alwon]

It also depends on the length of the conductors. A 10' piece with a 1 foot difference is much different than a 200' run with a 1' difference. I suspect one can get it closer than 1' hopefully within a few inches. LOL This comment is coming from a guy who has run parallel conductors less than 3 times in his life---

 

[iwire]

It also depends on the length of the conductors. A 10' piece with a 1 foot difference is much different than a 200' run with a 1' difference.

I agree and I think that is why G._S._Ohm was using percentages.

I would like to see the NEC give a percentage of allowable difference.