BarklieEstes
Member
- Location
- Richmond, VA
- Occupation
- Master Electrician
Greetings,
Under the 2017 NEC, what would the minimum conductor size be for a 40a inverter output circuit using 90° TC-ER cable? The inspector and I agree on the relevant codes [690.8 & 334.80] but disagree on how to apply them. For my part:
690.8(B)(1) says to multiply the maximum current by 125% with and not to shrink the allowable ampacity.
40 * 125% = 50a.
50a @ 90° Column = #8 conductor
690.8(B)(2) says to take the maximum current as is and to shrink the allowable ampacity. 334.80 shrinks it all the way down to the 60° Column.
40a @ 60 ° = #8 conductor
690.8(B) says to take the larger of (1) and (2), which would yield #8.
The inspector's argument, I believe, is that although 690.(B)(1) doesn't want you to shrink the allowable ampacity for some things (ambient temperatures, rooftop sunlight), it does still want you to shrink it for the purposes of 334.80. Therefore, you should increase the ampacity from 40a to 50a and shrink the allowable ampacity from the 90° to the 60° at the same time:
40 * 125% = 50a
50 @ 60° = #6 conductor
Thanks,
Barklie Estes
Under the 2017 NEC, what would the minimum conductor size be for a 40a inverter output circuit using 90° TC-ER cable? The inspector and I agree on the relevant codes [690.8 & 334.80] but disagree on how to apply them. For my part:
690.8(B)(1) says to multiply the maximum current by 125% with and not to shrink the allowable ampacity.
40 * 125% = 50a.
50a @ 90° Column = #8 conductor
690.8(B)(2) says to take the maximum current as is and to shrink the allowable ampacity. 334.80 shrinks it all the way down to the 60° Column.
40a @ 60 ° = #8 conductor
690.8(B) says to take the larger of (1) and (2), which would yield #8.
The inspector's argument, I believe, is that although 690.(B)(1) doesn't want you to shrink the allowable ampacity for some things (ambient temperatures, rooftop sunlight), it does still want you to shrink it for the purposes of 334.80. Therefore, you should increase the ampacity from 40a to 50a and shrink the allowable ampacity from the 90° to the 60° at the same time:
40 * 125% = 50a
50 @ 60° = #6 conductor
Thanks,
Barklie Estes