de-rating
- Thread starter rbs
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electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: de-rating
Me too.
Me too.
Re: de-rating
I have reviewed code book and web and am more confused than ever. New commercial type building. Do i de rate the lighting circuits? Do i de rate the receptacle circuits? Is up sizing all wire to #10 an accepted method? Is up sizing conduit (under filling) an accepted method? All panels are furnished with breakers will any of the above effect breaker size?
I have reviewed code book and web and am more confused than ever. New commercial type building. Do i de rate the lighting circuits? Do i de rate the receptacle circuits? Is up sizing all wire to #10 an accepted method? Is up sizing conduit (under filling) an accepted method? All panels are furnished with breakers will any of the above effect breaker size?
Re: de-rating
Not meaning to sound condescending, (although I'm sure it does) but I think you need to look into some educational material.
The NEC is not a training manual, and in fact there are books writen just for understanding it.
Roger
Not meaning to sound condescending, (although I'm sure it does) but I think you need to look into some educational material.
The NEC is not a training manual, and in fact there are books writen just for understanding it.
Roger
bphgravity
Senior Member
- Location
- Florida
Re: de-rating
Derating of conductors is only required for certain conditions. Adjustment factors include how many current-carrying conductors that are installed in a raceway, the ambient temperature surrounding the conductors, the type of insulation on the conductors, the type of loads that will be served (continuous, harmonic, etc.), the temperature ratings of terminals, and possibly a few others.
Start at section 310.15 of the NEC.
Derating of conductors is only required for certain conditions. Adjustment factors include how many current-carrying conductors that are installed in a raceway, the ambient temperature surrounding the conductors, the type of insulation on the conductors, the type of loads that will be served (continuous, harmonic, etc.), the temperature ratings of terminals, and possibly a few others.
Start at section 310.15 of the NEC.
Re: de-rating
I assume you are talking about branch circuits. I also assume you are talking about derating for # of wires in a conduit.
Point #1: Increasing the conduit size doesn't affect derating. 10 conductors in a 3" conduit get derated just like it was a 3/4" conduit.
Per 310.15, you derate to 70% for up to 9 current carrying wires in a conduit. If you use THHN/THWN wire, it is good for 30A at 90 deg. Thus, 30A * .7 = 21 amps. So you can put up to 4 20A branch circuits in a single conduit without having to derate #12 wire. (4 circuits * 2 current carrying wires each = 8 wires).
Steve
I assume you are talking about branch circuits. I also assume you are talking about derating for # of wires in a conduit.
Point #1: Increasing the conduit size doesn't affect derating. 10 conductors in a 3" conduit get derated just like it was a 3/4" conduit.
Per 310.15, you derate to 70% for up to 9 current carrying wires in a conduit. If you use THHN/THWN wire, it is good for 30A at 90 deg. Thus, 30A * .7 = 21 amps. So you can put up to 4 20A branch circuits in a single conduit without having to derate #12 wire. (4 circuits * 2 current carrying wires each = 8 wires).
Steve
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: de-rating
Mike Holts Understanding the NEC Volume 1 is excellent and a good start.
Mike Holts Understanding the NEC Volume 1 is excellent and a good start.
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