Conductor bending/parallel runs

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riverjig87

riverjig87

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Minot, North Dakota, USA
First, I have searched this forum and have found some related answers. However, I haven't found one that gives me a clear cut answer.

I have two runs of 600 THWN parallels. We have terminated them at the bottom of an equipment panel. Each phase terminal has a listed, double lug configuration.

Question 1. In order to maintain the requirements of installation of parallel conductors, must we form a loop in one (for example), A phase conductor in order to maintain the equal length as accurate as possible? (Looking at 8-10").

Question 2. It is a very tight space. In order to terminate the conductors, we have to form some bends in the wire in order to fit them. Is there a minimum bend radius for the wire? ( I have only been able to find an answer for conductors over 600v, art.300.34

I appreciate your help. Thank you.
 
riverjig87 said:
First, I have searched this forum and have found some related answers. However, I haven't found one that gives me a clear cut answer.

I have two runs of 600 THWN parallels. We have terminated them at the bottom of an equipment panel. Each phase terminal has a listed, double lug configuration.

Question 1. In order to maintain the requirements of installation of parallel conductors, must we form a loop in one (for example), A phase conductor in order to maintain the equal length as accurate as possible? (Looking at 8-10").

Question 2. It is a very tight space. In order to terminate the conductors, we have to form some bends in the wire in order to fit them. Is there a minimum bend radius for the wire? ( I have only been able to find an answer for conductors over 600v, art.300.34

I appreciate your help. Thank you.
Click to expand...
I am not sure what exactly you are looking for but look here
article 312.6(B) also look at article 314.28 (1)(2)
 
Dennis Alwon said:
I am not sure what exactly you are looking for but look here
article 312.6(B) also look at article 314.28 (1)(2)
Click to expand...
I believe you have to maintain equal length. A loop is a good way to do this.
 
riverjig87 said:
First, I have searched this forum and have found some related answers. However, I haven't found one that gives me a clear cut answer.

I have two runs of 600 THWN parallels. We have terminated them at the bottom of an equipment panel. Each phase terminal has a listed, double lug configuration.

Question 1. In order to maintain the requirements of installation of parallel conductors, must we form a loop in one (for example), A phase conductor in order to maintain the equal length as accurate as possible? (Looking at 8-10").

Question 2. It is a very tight space. In order to terminate the conductors, we have to form some bends in the wire in order to fit them. Is there a minimum bend radius for the wire? ( I have only been able to find an answer for conductors over 600v, art.300.34

I appreciate your help. Thank you.
Click to expand...
Check out 310.4. The paralleled conductors in each phase, neutral or grounded circuit conductor must have the same characteristics.
 
riverjig87 said:
Question 1. In order to maintain the requirements of installation of parallel conductors, must we form a loop in one (for example), A phase conductor in order to maintain the equal length as accurate as possible? (Looking at 8-10").
Click to expand...

The code states 'the conductors shall be the same length'.

You should do what you can to keep them as close to the same length. In reality as the code does not allow any tolerance in the length of the conductors all parallel installations should fail inspection as it is imposable for two conductors to be the same exact length.

Question 2. It is a very tight space. In order to terminate the conductors, we have to form some bends in the wire in order to fit them. Is there a minimum bend radius for the wire?
Click to expand...

There are no minimum bending radius rules for single conductors under 600 volt.
 
riverjig87 said:
I have two runs of 600 THWN parallels.
In order to maintain the requirements of installation of parallel conductors, must we form a loop in one . . . conductor in order to maintain the equal length as accurate as possible? (Looking at 8-10").
Click to expand...
I'm curious as to what percentage of the run that 8-10" is. In other words, how long is the run? If it's 10', I can see the concern. If it's 100, I don't believe it's enough to bother with the loop.

Is anyone aware of an "industry-accepted" tolerance?
 
O f course you realize the true lenght of this conductors will never be the same, right?

Have you taken into consideration the actual conduit runs? One run is never exactly the same as the other.

Even the path the actual wire takes will vary in length....one run has an "A" phase on the inside radius, while the other run may have a "B" phase on the inside radius.

Simply trying to maintain an equal distance for the portions visible is shooting in the dark.

Like Bob (Iwire) said:
In reality as the code does not allow any tolerance in the length of the conductors all parallel installations should fail inspection as it is imposable for two conductors to be the same exact length.
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This of course begs the question: how large is the inductance of this loop, and how does it compare with the resistance caused by a difference in the length of the runs.

-Jon
 
Look at table 8. 600 has 0.0223 ohms of resistance per 1000 ft. Will 8 or 10 inches make a differance? I recently did a 1000 amp 3 phase 480 service with 3 sets of four 500's. We landed them without trying to keep them exactly the same length in the ATS,transformer or gen set. A true rms amp probe showed equal current on all 3 conductors of the same phase. Anyone dissagree?
 
Pierre C Belarge said:
I would say that we could reference 110.3(B) and then follow the manufacturer's requirements as to the proper installation methods they will have for the different types of conductors that they may produce.
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Can you show me any info included in the listing and labeling from the manufacturers of say THHN, THWN, XHHW ect. that supports your view that there are minimum bending radii for these single conductors in an enclosure? (other than during pulling)
 
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Davis9 said:
There are many manufacturers of wire/cable. Most seem to have a minimum requirement of bending radius. Final positioning is usually half the pulling minimum.

Tom


http://www.cerrowire.com/default.aspx?id=77
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Tom, I saw that before that is merely a suggestion if not included with the listing and labeling of the product.

If 110.3(B) is to be cited those bending radius recommendations have to part of the listing.

Don't get me wrong, I am no hack, at the same time an inspector can not fail a job using 110.3(B) as a catch all, there must be some paperwork to back it up.
 
iwire said:
Tom, I saw that before that is merely a suggestion if not included with the listing and labeling of the product.

If 110.3(B) is to be cited those bending radius recommendations have to part of the listing.

Don't get me wrong, I am no hack, at the same time an inspector can not fail a job using 110.3(B) as a catch all, there must be some paperwork to back it up.
Click to expand...


I figured as much. 110.3(B) is used alot here(MikeHolt) but I've never truely encountered it in the field.

Tom

P.S. I've seen some pretty aweful things in some of the areas I work in and if 110.3(B) isn't used there then I wonder where it would be.
 
Will 8 or 10 inches make a differance?
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Assuming that all other aspects of the parallel installation are identical, then the change in length is a direct change in the resistance of the run. If you have a 10' run and a 9'3" run in parallel, then ~52% of the current will be on the 9'3" run and 48% on the 10'. This would not be a problem in most cases.
Don
 
This might help

This might help

Thanks for all the feedback. This is what I got doing some in-depth research..

The min. conductor bending radius is only specified in the NEC for conductors above 600v. Conductors below 600v have a minimum bending radius set forth by the manufacturer of that particular conductor. I think I read that one person had mentioned this as well in one of the replies. So, we obtained the chart from Southwire and found we were well within the specified bending requirements.

As far as the parallel conductor length, I agree with everyone whom feels that you must get as close as possible. We went ahead and did form some bends in the conductors in order to maintain the equal length. We did attach a meter to the parallel conductors to show our inspector that we installed our system correctly by having the exact same lengths on all our conductors.

Thanks everyone for the feedback.
 
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