Should size change if cable #1 is romex what if cable #1 is SE?

H

hhsting

Senior Member
Location
Glen bunie, md, us
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Junior plan reviewer
The scenario is this is townhome so service and feeders supply entire townhome would be 83%. Would the size of cable #1 in the attached shot phase/neutral conductors change if its romex? How about if its SE cables?
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infinity said:
NM cable is available only up to #2 AWG so that cannot be used. Since these are tap conductors they need to be sized according to the 200 camp OCPD.
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Cable #1 is not tap conductors. They supply entire townhome load and allowed to be 83% of the service.


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hhsting said:
Cable #1 is not tap conductors. They supply entire townhome load and allowed to be 83% of the service.


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Yes you're correct I mixed this up with the other thread. Yes the #4/0 aluminum is correct. I removed the incorrect info.
 
Still can't get NM cable larger than 2 AWG though, isn't the overcurrent device 200 amps? Could use #2 copper for a 125 amp feeder here.
 
NM cable is prohibited for service entrances, so that portion of cable 1 from meter to disconnect can't be NM cable. For the others, if NM was made large enough, it would have to be larger because of its 60C limitation. But SE or individual conductors would most likely be the same size because of 75C ratings.
 
suemarkp said:
For the others, if NM was made large enough, it would have to be larger because of its 60C limitation. But SE or individual conductors would most likely be the same size because of 75C ratings.
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Why would the 60° C or 75° C come into play for a feeder using NM cable? 310.12(B) says that if they're are no adjustment factors then the Table 310.12 can be used. There are no temperature limits mentioned for that table.

310.12(B) Feeders.
For a feeder rated 100 amperes through 400 amperes, the feeder conductors supplying the entire load associated with a one-family dwelling, or the feeder conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the feeder rating. If no adjustment or correction factors are required, Table 310.12 shall be permitted to be applied.
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infinity said:
Why would the 60° C or 75° C come into play for a feeder using NM cable? 310.12(B) says that if they're are no adjustment factors then the Table 310.12 can be used. There are no temperature limits mentioned for that table.
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But other sections of the Code (334) limit NM to the 60c table. Wouldn’t that apply across the board?

And to the OP, if some of those runs are exterior, even in conduit, NM is not permitted.
 
Seven-Delta-FortyOne said:
But other sections of the Code (334) limit NM to the 60c table. Wouldn’t that apply across the board?
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I think that this just fell through the cracks when the added the table back into the NEC. There is no mention anywhere in 310.12 stating that you would need to consider the temperature rating of NM cable if used. Also there is no prohibition of using NM cable for the feeder. It does mention 83% which may contradict the wording stating that you can use the table.
 
infinity said:
I think that this just fell through the cracks when the added the table back into the NEC. There is no mention anywhere in 310.12 stating that you would need to consider the temperature rating of NM cable if used. Also there is no prohibition of using NM cable for the feeder. It does mention 83% which may contradict the wording stating that you can use the table.
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I thought it doesnt matter their is no NM cable larger than #2 awg in market? They dont make it
 
The question would be valid if the service was 100A instead of 200A so you were debating #4 NM -vs- #4 anything else. You still can't use NM for a service, but you could for a feeder. I'm thinking like Infinity that table 310.12 has an oversight for NM cable. In previous version of the code when it was table 310.15(B)(6), it has cable type restrictions of RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2. NM was not on that list.
 
suemarkp said:
The question would be valid if the service was 100A instead of 200A so you were debating #4 NM -vs- #4 anything else. You still can't use NM for a service, but you could for a feeder. I'm thinking like Infinity that table 310.12 has an oversight for NM cable. In previous version of the code when it was table 310.15(B)(6), it has cable type restrictions of RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2. NM was not on that list.
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Why would question be valid for 100A but not 200A service??
 
infinity said:
Why would the 60° C or 75° C come into play for a feeder using NM cable? 310.12(B) says that if they're are no adjustment factors then the Table 310.12 can be used. There are no temperature limits mentioned for that table.
Click to expand...
infinity said:
I think that this just fell through the cracks when the added the table back into the NEC. There is no mention anywhere in 310.12 stating that you would need to consider the temperature rating of NM cable if used. Also there is no prohibition of using NM cable for the feeder. It does mention 83% which may contradict the wording stating that you can use the table.
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334.80 references the 60oC for NM as the final limit even if the derating or no derating needed of the conductor using the starting point of 90oC is higher than the 60oC limit. So it doesn't need to be in 310.

First sentence of 334.80 says:
The ampacity of Types NM and NMC cable shall be determined in accordance with 310.14
So you can't use 310.12 table for NM cable.
hhsting said:
I thought it doesnt matter their is no NM cable larger than #2 awg in market? They dont make it
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334.104 limits NM from 14 to #2 AWG so probably why they don't make it.
 
suemarkp said:
The question would be valid if the service was 100A instead of 200A so you were debating #4 NM -vs- #4 anything else. You still can't use NM for a service, but you could for a feeder. I'm thinking like Infinity that table 310.12 has an oversight for NM cable. In previous version of the code when it was table 310.15(B)(6), it has cable type restrictions of RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2. NM was not on that list.
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That's what I'm saying. You're correct the old table from a few code cycles ago listed specific types. The new version of 310.12 does not and it tells us that we can use the table without restrictions for NM.
 
infinity said:
That's what I'm saying. You're correct the old table from a few code cycles ago listed specific types. The new version of 310.12 does not and it tells us that we can use the table without restrictions for NM.
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But you can't use that reference in the absence of consideration of the reference in 334.80 that says you must use 310.14 and not 310.12.
 
infinity said:
The new version of 310.12 does not and it tells us that we can use the table without restrictions for NM.
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That's an oversight fixed in the 2026 NEC First Draft. The last sentence of 310.12(A) and (B) becomes "If no adjustment or correction factors are required, Table 310.12(A) shall be permitted to be applied for conductors or cables rated 75°C (167°F) or greater."

Cheers, Wayne
 
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