wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I thought I'd start posting some of the 19 PIs I've submitted so far for the next NEC. Here's the first one by location in the NEC.
Cheers, Wayne
Ampacity. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceedingits the temperature rating of it or its wiring method.
Statement of Problem and Substantiation for Public Input
The wiring method within which a conductor is installed may limit the maximum allowable operating temperature of the conductor. Namely, for LFMC 350.10(4); PVC 352.10(J); HDPE 353.10(6); RTRC 355.10(I); LFNC 356.10(9); and ENT 362.10(10). There is some confusion in the field about whether the limitations in the enumerated sections cause a reduction of ampacity, or whether they are an additional restriction that applies independent of ampacity.
For example, say #8 Cu THWN is installed in LFMC in a wet location for an application with 75C terminations and with no ampacity adjustment or correction required. All LFMC is limited to a 60C wet location rating per UL standard 360. Is (A) the ampacity of the #8 Cu THWN within the LFMC 40A, because 350.10(4) limits the conductor maximum operating temperature to 60C? Or is (B) the ampacity still 50A per the 75C rating of the THWN, but 350.10(4) imposes a separate restriction that the conductor may never be used for more than 40A?
This distinction makes a difference for the case of a 40A continuous load--that application requires a 50A ampacity conductor per 210.19(A)(1)(a), although the conductor is never expected to see a load exceeding 40A. So under interpretation (A) the connected load could not be a 40A continuous load, because 350.10(4) lowers the conductor ampacity; while under interpretation (B), the connected load could be a 40A continuous load, as the ampacity is still 50A, and the operating current does not exceed 40A.
The proposed definitional change would clarify the confusion in favor of interpretation (A), that the conductor ampacity is reduced within the LFMC.
Cheers, Wayne
Ampacity. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding
Statement of Problem and Substantiation for Public Input
The wiring method within which a conductor is installed may limit the maximum allowable operating temperature of the conductor. Namely, for LFMC 350.10(4); PVC 352.10(J); HDPE 353.10(6); RTRC 355.10(I); LFNC 356.10(9); and ENT 362.10(10). There is some confusion in the field about whether the limitations in the enumerated sections cause a reduction of ampacity, or whether they are an additional restriction that applies independent of ampacity.
For example, say #8 Cu THWN is installed in LFMC in a wet location for an application with 75C terminations and with no ampacity adjustment or correction required. All LFMC is limited to a 60C wet location rating per UL standard 360. Is (A) the ampacity of the #8 Cu THWN within the LFMC 40A, because 350.10(4) limits the conductor maximum operating temperature to 60C? Or is (B) the ampacity still 50A per the 75C rating of the THWN, but 350.10(4) imposes a separate restriction that the conductor may never be used for more than 40A?
This distinction makes a difference for the case of a 40A continuous load--that application requires a 50A ampacity conductor per 210.19(A)(1)(a), although the conductor is never expected to see a load exceeding 40A. So under interpretation (A) the connected load could not be a 40A continuous load, because 350.10(4) lowers the conductor ampacity; while under interpretation (B), the connected load could be a 40A continuous load, as the ampacity is still 50A, and the operating current does not exceed 40A.
The proposed definitional change would clarify the confusion in favor of interpretation (A), that the conductor ampacity is reduced within the LFMC.
