Conductors in Parallel

[jap]

Do you feel parallel conductors are ever truly the same lenghth ?
I think not.

Especially if your running 2 seperate conduits.
Say for instance you pulled in 1 set of conductors in 1 of 2 parallel conduits and cut and terminated both ends of the conductor you just pulled into pipe #1.

Then turned right aroud and took what you just terminated loose, pulled that wire out of pipe #1 and pulled it back into pipe #2 and tried to reterminate it. I'd almost guarantee they would not fall exactly back into place as it did the first time you terminated it.

Is there any lee way on the requirement of parallel conductors being the same length?

 

[electrofelon]

Do you feel parallel conductors are ever truly the same lenghth ?
I think not.

Especially if your running 2 seperate conduits.
Say for instance you pulled in 1 set of conductors in 1 of 2 parallel conduits and cut and terminated both ends of the conductor you just pulled into pipe #1.

Then turned right aroud and took what you just terminated loose, pulled that wire out of pipe #1 and pulled it back into pipe #2 and tried to reterminate it. I'd almost guarantee they would not fall exactly back into place as it did the first time you terminated it.

Is there any lee way on the requirement of parallel conductors being the same length?

I typically lay the conductors on the ground and measure them. Funny you should post this though as I have some parallels to install tomorrow and i was wondering how much a given length difference would effect current. Could have done some math but I didnt want to know that badly

 

[GoldDigger]

I typically lay the conductors on the ground and measure them. Funny you should post this though as I have some parallels to install tomorrow and i was wondering how much a given length difference would effect current. Could have done some math but I didnt want to know that badly

Rule of thumb for parallel resistances (for small differences between nominally equal resistances) is that a 1% difference in resistance will cause s 1% imbalance in current. And because of the contributions of the terminations at each end, a 1% difference in length will be less than a 1% difference in branch resistance.

 

[ActionDave]

Do you feel parallel conductors are ever truly the same lenghth ?
I think not.

The journeyman I learned under would do his best to make sure they were.

He would start with equal length conductors, make up one end them move to the other; grab one conductor, see where it needed to land cut it off and land it, save the scrap and use it to measure how much to cut off all the others.

Then he would weave, bend, curl, cuss, kick the conductors, cuss some more, bend the conductors the other way, curl them around his forearm and stuff them in the panel, cuss, cuss, cuss, pull them out, step on them, cuss some more, stuff them back in, give the ones that needed it another good kick, land and tighten everything. After that we got to go home.

Sometimes it was before sundown, other times I had to pull the truck around and shine the headlights toward where we were working.

There is no leeway in the code. Parallel conductors have to be the same length.

 

[Wilg]

You must have learned from the same guys I did. They were sticklers that all conductors were exactly equal in length. We would pull them out across the parking lot if needed.
I went on to work for a larger firm and on the first parallel pull the guys just pulled them into the panel and chopped them at the lugs. When I asked why they said "it don't matter...nobody ever checks anyway".:blink:

 

[jap]

If 2 pipes rise side by siide vertically up from a Panel then turn horizontally (flat) and travel some distance, then make a horizontal bend to the righ or left , then turn verically down into another panel. there's no way the wire in both pipes could be exactly the same length. The spacing between the pipes themselves and the radius of the outside 90 would make the 2 runs different lengths to begin with, regardless if you tried to keep them the same length where they terminate.

 

[don_resqcapt19]

The code gives no allowance for the differences in length that will almost always exist in a parallel installation. I guess you could say that the code does not really permit parallel installations.

 

[ActionDave]

If 2 pipes rise side by siide vertically up from a Panel then turn horizontally (flat) and travel some distance, then make a horizontal bend to the righ or left , then turn verically down into another panel. there's no way the wire in both pipes could be exactly the same length. The spacing between the pipes themselves and the radius of the outside 90 would make the 2 runs different lengths to begin with, regardless if you tried to keep them the same length where they terminate.

The conductors do not appear to have the same length where they emerge in the gear no doubt.

 

[jap]

The code gives no allowance for the differences in length that will almost always exist in a parallel installation. I guess you could say that the code does not really permit parallel installations.

As odd as that sounds that is exactly correct. until the requirement is reworded somehow.

 

[jap]

We may have to just add a turn here or there in our pipe runs to make the two even out.
i could see where an even number of horizontal 90d bends in a run might get them closer, but with an odd number of horizontal 90d bends, one would always be longer thaan the other, even if there was no spacing between the pipes. On Verticle 90d Bends not so much

 

[iwire]

As odd as that sounds that is exactly correct. until the requirement is reworded somehow.

It is correct, the current wording is impossible to comply with.

 

[GoldDigger]

It is correct, the current wording is impossible to comply with.

And yet we recognize that a difference limit of 1% of the run length plus six inches is probably a perfectly reasonable standard to apply for our own personal satisfaction.
For the CMP to get the code language to define a usable standard would require them first to understand what happens when parallel conductors are used, second to make it clear what "parallel conductors" actually means (take a look at the loop circuit and multiple switch threads to see more about that), third to decide on a reasonable standard and fourth to agree on wording to make it all happen.
All when it is "obvious" what is really meant.
I am not holding my breath.

 

[iwire]

And yet we recognize that a difference limit of 1% of the run length plus six inches is probably a perfectly reasonable standard to apply for our own personal satisfaction.
For the CMP to get the code language to define a usable standard would require them first to understand what happens when parallel conductors are used, second to make it clear what "parallel conductors" actually means (take a look at the loop circuit and multiple switch threads to see more about that), third to decide on a reasonable standard and fourth to agree on wording to make it all happen.
All when it is "obvious" what is really meant.
I am not holding my breath.

I am sure there was supposed to be a point in there but it went right past me.

 

[GoldDigger]

I am sure there was supposed to be a point in there but it went right past me.

Just agreeing that the current code language cannot be implemented and yet people get away with it all the time, with varying degrees or necessary or unnecessary pain in the process.
And then despairing of anything changing in the foreseeable future.