OCPD SIZE
- Thread starter frank
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- Bremerton, Washington
- Occupation
- Master Electrician
Re: OCPD SIZE
For derating, ampacity of 12 THHN is 30 amps, but after derating can exceed 20 amps, but see section 240.3
Derating is given in Table 310-15(b)(a). If there were 15 current carrying conductors you would derate 50%. But are all the conductors current carrying? Typically grounded conductors don't count, unless for harmonic loads.
The amount of current does not matter, the circuit ampacity is determined by the OCPD.
For derating, ampacity of 12 THHN is 30 amps, but after derating can exceed 20 amps, but see section 240.3
Derating is given in Table 310-15(b)(a). If there were 15 current carrying conductors you would derate 50%. But are all the conductors current carrying? Typically grounded conductors don't count, unless for harmonic loads.
The amount of current does not matter, the circuit ampacity is determined by the OCPD.
russ
Senior Member
- Location
- Burbank IL
Re: OCPD SIZE
240.3(B) restricts you from useing the next higher standard overcurrent device for multioutlet branch circuits.
You can use the 90degree column for thhn derating, 50% of 30amps = 15.
Russ
[ March 26, 2003, 12:21 AM: Message edited by: russ ]
240.3(B) restricts you from useing the next higher standard overcurrent device for multioutlet branch circuits.
You can use the 90degree column for thhn derating, 50% of 30amps = 15.
Russ
[ March 26, 2003, 12:21 AM: Message edited by: russ ]
Re: OCPD SIZE
Frank, I am curious how your circuits are configured. By that I mean are there 5 circuits with L-N-G, or what? You only have to count the current carrying conductors. For example if you are supplying from a 208Y/120 you would not be required to count the neutral.
Otherwise if you have 15 current carrying conductors in a conduit with 20-amp breakers you are going to have to use 10 AWG or use two seperate conduits.
Frank, I am curious how your circuits are configured. By that I mean are there 5 circuits with L-N-G, or what? You only have to count the current carrying conductors. For example if you are supplying from a 208Y/120 you would not be required to count the neutral.
Otherwise if you have 15 current carrying conductors in a conduit with 20-amp breakers you are going to have to use 10 AWG or use two seperate conduits.
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