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The ampacity of 12 AWG THHN is 30 amps per table 310.16. However 110.14 (C) generally limits its rating to 25 amps 240.4 (D) does not change the rating of 12 AWG THHN but often requires it to be protected at 20 amps. Table 240.4 (G) lists the types of circuits where 12 AWG can be protected above 20 amps.
For example, SOOW cable is reduced in maximum carrying amperage compare to THHN for same wire gauge due to the thick multi-layer casing of SOOW which restricts ability of wire to dissipate heat. Each current carrying wire in an enclosure adds to the heating per unit length so there is derating for multiple current carrying conductors.
It is certainly easier with solid. Places where back stabbing is common probably prefer solid. There are a fair number of electricians who don't like back stabbing and blame it for all kinds of ills that it probably does not deserve. Personally I do not like trying to connect stranded wire to receptacles and switches.
Table 310.16 indicates that for #12 THHN the maximum allowed ampacity is 30 Amps. 70% of 30 Amps is 21 Amps. Footnote to Table 310.16 refers to 240.4(D) which states OCP cannot exceed 20 Amps for a #12 conductor. The OCP required by 240.4(D) is less than the derated circuit calculation by one amp.
a)THHN Construction ? Jacketed insulation for a Type NM or NMC cable shall have a nylon or similar jacket and shall comply with the thickness and other applicable requirements for Type THHN thermoplastic-insulated wire without (see 25.18) any surface marking of ?THHN?, ?-B? or any ampacity or temperature rating. b)TW Construction ?
Re: minimum bending radius THHN If we cannot make a very sharp 90 degree bend in #12 and smaller wire, how it it possible to wrap it around a wire binding terminal/screw? Actually, per UL508A for control panels, wire bending space for #14-10 is not specified. However, for field terminations a wire binding screw for #10 and #12 must be at least ...
Start with the fact that THHN wire is rated for a 90C rise above the ambient of 30C, and with the fact that at 90C #12 THHN has an ampacity of 30 amps. Now apply the derating factors of Table 310.15(B)(2)(a).
Feb 1, 2007. #2. rjhavens1 said: I am installing a peice of equipment on and existing curcuit that has a 25a breaker and 12g wire. Is 12g sufficient for a 25a curcuit, it is 3 phase commercial. Usually not unless you are feeding an a/c or something that allows you to fuse over the wire size. #12 THHN is good for a 20 amp breaker not 25.
I told my boss today that you can put 7-9 #12 AWG current carrying conductors into a 3/4" pipe each protected by a 20amp breaker. I used table 310.15(b)(16) and 310.15(C)(1) to calculate that 7-9 #12s in a conduit can be rated at 21amps. My boss claims that I can't use the 90 degree column to...
Per table 310.15 (B) (16)----under the 75 deg column #12 can carry 25 amps, But, it has 2 asterisk symbols, and refers you to 240.4 (D) (5)--12 AWG copper 20 amp. I understand that #12 THHN copper at 75 deg, can only handle 20 amps. per the NEC. Question, I am interpreting that correctly, and anything higher like 25 or 30