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Old 04-03-2011, 08:20 AM   #1
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wires bunched together


All,
A question about running wires together. Our local code states that if running more than a 2ft together.... the max no of 14,2s can be three.

Why? My thoughts are that if the proper wiring is used for a load, there should not be heat build up...why the restriction? Something about voltage drop?
Thanks

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Old 04-03-2011, 08:39 AM   #2
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wires bunched together


youll have heat buildup regardless to some degree, (heres some basic physics)

copper has resistance and resistance creates heat with regard to current flowing through it.......

FURTHERMORE, if temperature increases in conductors (because they are bundled), the resistance increases, therefore reducing the maximum safe current......

As far as heat transfer/dissipation, CONDUCTION is more efficient means of heat xfer than conduction, if you have those wires together they will xfer more heat to each other than to the air....

Romex is rated for 60 degrees celcius, anything over that is unsafe and you must derate the wire......now service entrance is rated 75c and THHN is rated 90c, you can put more current through THHN than through NMB/UF......look at the 310 NEC ampacity charts.

It has nothing to do with voltage drop.

Look into the NEC appendixes in relation to conduit fill.......same applies.....'

to my understanding you can run them close to each other (a few inches apart) just not inside the same arbor holes, under the same staples etc.......just not bundled....

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Old 04-03-2011, 08:51 AM   #3
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wires bunched together


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Originally Posted by LyonsElecSupply View Post
As far as heat transfer/dissipation, CONDUCTION is more efficient means of heat xfer than conduction, if you have those wires together they will xfer more heat to each other than to the air....
OK, I'm confused..... as usual.....

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Old 04-03-2011, 09:43 AM   #4
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wires bunched together


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Originally Posted by gkaro View Post
All,
A question about running wires together. Our local code states that if running more than a 2ft together.... the max no of 14,2s can be three.
This has to be a local amendment. I would hope they have it in writing somewhere.
The NEC, although NOT expressly stated, limits the maximum number of #14, #12, or #10 cables bundled to four, or up nine current carrying conductors, before derating needs to be considered.
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Old 04-03-2011, 09:44 AM   #5
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wires bunched together


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Originally Posted by Powerup26 View Post
What about when I use stack its??? Thats 8wires max I have together. I smell a "mr.knowitall"
Cables run in Stack-its are NOT considered bundled due to the intentional spacing provided.
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