distance for which percent fill does not apply

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mshields

Senior Member
Location
Boston, MA
Article 310.15 defines the number of conductors in a conduit limits before having to derate. I'm running multiple circuits to a pull box above the ceiling and then down via multiple 2 inch conduits into the panelboard below. I'm doing this because it's a 60 pole panel and if I bring in an MC cable for each circuit, they won't all fit in the top of a 20" by 6" panel top.

Is this permissible without derating given that I'm only running these multiple conductors in 2 inch conduit for about 4 feet?

Thanks,

Mike
 

GoldDigger

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Article 310.15 defines the number of conductors in a conduit limits before having to derate. I'm running multiple circuits to a pull box above the ceiling and then down via multiple 2 inch conduits into the panelboard below. I'm doing this because it's a 60 pole panel and if I bring in an MC cable for each circuit, they won't all fit in the top of a 20" by 6" panel top.

Is this permissible without derating given that I'm only running these multiple conductors in 2 inch conduit for about 4 feet?

Thanks,

Mike
Look at 310.15(A)(2) [2011] (the ten feet or ten percent rule) and see if that gives you the relief that you need.
 

infinity

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New Jersey
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Since you asked about fill generally raceways with 3 or more conductors are limited to 40% fill, nipples (raceways 24" or less) can have up to 60% fill. The same 24" length would allow to avoid derating adjustments.
 

Smart $

Esteemed Member
Location
Ohio
If you go over the 24" mentioned by Rob, and the 310.15(A)(2) Exception doesn't help, consider running 2?2 wireway between pull box and panel, as CCC derating doesn't apply until you go over 30.... but you'll be limited to 20% fill.
 
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Smart $

Esteemed Member
Location
Ohio
Just a rough calculation, but if each of the 60 breakers was a 2-wire 120V circuit, that'd be 120 CCC's. If #12 THHN@.0133 in? per, 1.6 in? total. Divided by 20% is 8 in?... which would be (2) 2?2 wireways... but you'd be over the 30 CCC limit without derating. You'd have to go with (4) 2?2 wireways, 30 conductors, 10% fill each.
 
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mshields

Senior Member
Location
Boston, MA
How about this for a loopole

How about this for a loopole

A colleague of mine points out that most of the circuits we're talking about on a 208Y/120V panel are receptacle circuits. We never put more than 6 receptacles on a circuit; 6 x 180 = 1080W which is 9Amps.

Therefore, if the rules say we have to derate a 20Amp circuit by 50% we're all set.

My immediate reaction is that obviously someone could come along and add receptacles some point down the line. I'm wondering if there is anything explicitly disallowing this.

What do you think?

Thanks,

Mike
 

david luchini

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Connecticut
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Engineer
A colleague of mine points out that most of the circuits we're talking about on a 208Y/120V panel are receptacle circuits. We never put more than 6 receptacles on a circuit; 6 x 180 = 1080W which is 9Amps.

Therefore, if the rules say we have to derate a 20Amp circuit by 50% we're all set.

If you are derating your 20A receptacles circuits by 50%, you will need to start with a 40A conductor (#10 @ 90deg, or #8 @ 75deg.)
 

Nom Deplume

Senior Member
Location
USA
Mike, If the project is in MA then we have an amendment to the fill derateing that is in our favor.

Check 310.15(B)(3)(a) MA Amendment

So at 42 CCC you would need to derate to 60% of 30 amps. That would be 18 amps and good for a 20 amp CB based on your calculated load.

I would use 1-1/4" or 1-1/2" instead of 2" and run an extra one.
 
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infinity

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Location
New Jersey
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Journeyman Electrician
Next standard size up rule works for lighting and single receptacles but not multi-receptacle circuits.
 
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