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Old 06-18-2011, 07:07 PM   #16
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Wire size to 100 AMP subpanel


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the NEC tables are conservative.. there is a lot of wire in those cables.
Ummmm.......WHAT??


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...there are also derating factors such as duty %, load type etc..
Ummmm.......WHAT??


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...but generally you don't fill your panel more than 80% (80Amps)
Ummmm.......WHAT??

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Old 06-18-2011, 07:30 PM   #17
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Wire size to 100 AMP subpanel


Me thinx kbsparky in wrong column. THHN is rated 90 C not 75 C; and thus, 115 according to 2011 NEC Code Table 310.15(B)(16) formerly 310.16. It can be confusing with all the types of wire.
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Old 06-18-2011, 07:33 PM   #18
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Wire size to 100 AMP subpanel


Not quite. You can not use the 90 degree column for final connections unless you have equipment terminations rated at that temperature.

All the breaker box manufacturers that I am aware only have their terminations rated at 75 degrees, thus you are limited to wire with that capacity/rating.

You can start with the 90 degree ratings before any adjustments are made for things like ambient temperature and conduit fill deratings, but your final figure is restricted to the 75 degree values or less.
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Old 06-18-2011, 07:45 PM   #19
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Wire size to 100 AMP subpanel


what i mean is.. the 12 gauge wire can take more than 20Amps.. before it has any problems. but your local code does not allow it, so this is what i mean by conservative.

duty %, i am refering to that not all the loads are on at any one time. for instance, a 100A panel with 30 slots, even if they were all just 15 Amp breakers, would be 450Amps. obviously the idea is that not all the breakers will be on giving full power to the load. so this is what i mean by duty.

not filling more than 80%, i am refering to CEC (i don't know if it is in NEC) where it talks about if you don't know what the load is, then don't fill more than 80%. that is just from memory.. section 8, part I.

didn't mean to lead anyone astray..
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Old 06-18-2011, 07:47 PM   #20
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You posted this in the wrong thread, knucklez
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Old 06-18-2011, 07:50 PM   #21
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Wire size to 100 AMP subpanel


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Me thinx kbsparky in wrong column. THHN is rated 90 C not 75 C; and thus, 115 according to 2011 NEC Code Table 310.15(B)(16) formerly 310.16. It can be confusing with all the types of wire.
Aside from the fact that we are talking about NM cable, which is limited to the 60 deg C column.
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Old 06-18-2011, 08:03 PM   #22
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Wire size to 100 AMP subpanel


No we weren't. As stated previously, you can't get #3 in NM cable. This part of the discussion is definitely about #3 THHN/THWN.
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Old 06-19-2011, 06:28 PM   #23
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Wire size to 100 AMP subpanel


kbsparky and I are on #3 THHN we dropped the Romex #2/3 line of inquiry.

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