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Joined: Apr 2002
Posts: 178
R
Member
Yesterday we went to a plant where some conductors melted in the conduit.There was several problems all the circuits were over loaded #12`s 20+ amps about 19 8' floresant on each cir.They have 1 1/4 conduit with 36 # 12 conductors all over loaded and the conduit is very hot.The question I have how best to explain to the electrical poeple How to size the number of circuits in a pipe.The code table c8 says they can have 45 in the pipe but I tried explaining that with the ciruits over loaded and the heat generated the fill and current carrying capasity of the wires would be less.I don`t think I did a good job with them understanding so please help us out with some examples and code articals thanks guys.We ran another 1 1/4 conduit over and that reduced the heat and we split the circuits droping the current to each circuit.

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Joined: Mar 2001
Posts: 2,056
R
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See table 310.15(B)(2)(a) for adjustment factors.
36 conductors require an ampacity adjustment that results in only 40% of the Table 310.16 values.
In your case (using the 90c column for derating purposes) .4 x 30 amps = 12 amps for #12 copper.

Joined: Jan 2001
Posts: 75
G
Member
Is that 36 ungrounded conductors plus neutrals ?

Many plants have 3Ø 4W so the neutrals would be current carrying also on circuits with ballasts.

If so, could be 35 percent derate.
30A * 0.35 = 10.5 Ampacity.


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