The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

   
Topic Options
Rate This Topic
#9913 - 05/20/02 05:51 PM Parallel conductors
rmiell Offline
Member
Registered: 11/09/00
Posts: 261
Loc: La Junta, Co. USA
How important is the rule for parallel conductors to be equal length?

Is there any leeway?

I am installing a set of 4 (phase A, B, C & Neutral) in a 4" PVC conduit, 6 times, for a 2000amp service.

How would you handle the length issue in this installation? Cut all the same length, based on the longest, and loop where needed?

What method is best to help train this wire? Has anyone used that new device that fits on a ratchet? I saw one at a trade show, looked like a good idea.

Any hints on how to do this?

Thanks in advance.

Rick Miell
Top
Work Gear for Electricians and the Trades
#9914 - 05/20/02 07:33 PM Re: Parallel conductors
resqcapt19 Offline
Member
Registered: 11/10/00
Posts: 2209
Loc: IL
Rick,
The shorter the length of wire and the higher the load, the more critical the length becomes. I normally lay the conductors out and cut them all the same length before installing them. Finding space for the excess wire is sometimes a problem.
If you look at your installation and assume 4 sets of 600 kcmil with a calculated load of 1680 amps and multiple service disconnects and cable lengths of 20', 21', 22' and 23', we will find that the two shortest cables will be carryign more than there rated 75 degree ampacity. The 21' would be at 452, the 21' at 428, the 22' at 409 and the 23' at 391 amps. The rated ampacity of 600 kcmil is 420 amps.
Don(resqcapt19)
_________________________
Don(resqcapt19)
Top
#9915 - 05/20/02 07:39 PM Re: Parallel conductors
The Watt Doctor Offline
Member
Registered: 12/23/01
Posts: 443
Loc: Mont Belvieu, TX
Rick,
It is important to get them close, but reality says that there will be some difference because all of the conduits don't enter the service equipment in the same place. I can't speak for the ratchet device. I've always used a hydraulic wire bender.
I used to have a problem from a class that I took that showed in theory how important it is to have the conductors the same length.
Good Luck, and let us know how the installation turns out.

Regards,
Doc
_________________________
The Watt Doctor
Altura Cogen
Channelview, TX
Top
#9916 - 11/10/03 09:01 AM Re: Parallel conductors
Electra Offline
Member
Registered: 07/29/02
Posts: 38
Loc: Portland, Oregon, USA
I need to find out how inspectors are treating this rule that all conductors need to be the same length. Is there any standard percentage length difference that they allow?

I find that if there is a 10% difference in length between two conductors, there is approximately a 10% difference in the current through each conductor, with the shorter conductor carrying the larger portion of the current.

Also, do inspectors look at the whole installation as to how important it is for conductor length to be exactly the same.

For example, if you have 2 parallel - 1/0 conductors, 75C rated 150A feeding a 300A load. If there is any difference in length between the conductors, the shorter conductor would exceed it's ampacity rating.

But, if those same two conductors are feeding a 250A load, the ampacity of the shorter conductor is not exceed until it there is over a 30% difference in wire length.

Can anyone help me here?

Thanks,

Laura Jenkins
IBEW 48
Top
#9917 - 11/10/03 09:29 AM Re: Parallel conductors
GETELECTRIC Offline
Member
Registered: 10/22/03
Posts: 178
Loc: toronto canada
for the length i have always worked that the shortest should be within 2%of the longest,
Top
#9918 - 11/10/03 09:40 AM Re: Parallel conductors
Electra Offline
Member
Registered: 07/29/02
Posts: 38
Loc: Portland, Oregon, USA
Are you basing that 2% off of anything in particular?

Laura
Top
#9919 - 11/10/03 10:51 AM Re: Parallel conductors
GETELECTRIC Offline
Member
Registered: 10/22/03
Posts: 178
Loc: toronto canada
i am a canadian electrician and was taught this many moons ago,but if i have time i will look through the code book to see if i can locate this rule.
Top

Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box

Recent Posts
Forum Styles
by Admin
Today at 02:08 AM
License exam
by TRUE POWER
Yesterday at 09:16 PM
Looking for older post
by sparkyinak
Yesterday at 12:27 AM
Members: Non-Members: Did you know?
by Admin
01/22/17 02:34 PM
Safety at heights?
by HotLine1
01/21/17 08:51 PM

Who's Online
0 registered (), 79 Guests and 12 Spiders online.
Key: Admin, Global Mod, Mod
New in the Gallery:
Desk-mounted "power-board"
Top Posters
gfretwell 9066
Trumpy 8560
pauluk 7693
HotLine1 6833
sparky 5545
Member Spotlight
Member Since: 11/11/05
Posts: 190

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals