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

[infinity]

Well I would need only 166A. Whats the largest size its made?

It's right in the codebook.

334.104 Conductors.
The 600-volt insulated power conductors shall be sizes 14 AWG through 2 AWG copper conductors or sizes 12 AWG through 2 AWG aluminum or copper-clad aluminum conductors. Control and signaling conductors shall be no smaller than 18 AWG copper.

 

[roger]

I thought it doesnt matter their is no NM cable larger than #2 awg in market? They dont make it

Is it there or their?

 

[hhsting]

Is it there or their?

There


Sent from my iPhone using Tapatalk

 

[roger]

There


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[ramsy]

The new version of 310.12 does not and it tells us that we can use the table without restrictions for NM.

Since we are fixing mistakes, are you gona fix all the NM you installed illegally, under Table 310.12

 

[infinity]

Since we are fixing mistakes, are you gona fix all the NM you installed illegally, under Table 310.12

When two code sections conflict which one applies?

 

[retirede]

When two code sections conflict which one applies?

The one you violate!

 

[infinity]

The one you violate!

If that were the case then T310.12 wouldn't be able to be applied to anything because the conductors are too small for the listed amp ratings in the table. T310.12 overrides other ampacity sections of the code so It can be applied to NM cable.

 

[wwhitney]

T310.12 overrides other ampacity sections of the code so It can be applied to NM cable.

It was never intended to apply to NM cable; see post #16. So why the loophole exists currently, it is unwise to use it.

Cheers, Wayne

 

[tortuga]

I agree with Fred, when you choose the NM wiring method the ampacity restrictions of that wiring method would prevail over more general ampacity tables, there is no issue to fix;

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.

That's an oversight fixed in the 2026 NEC First Draft.

The oversight in 310.12 in recent years is they forgot where the ampacity adjustment came from in the first place, it was originally based on 2 CC in a raceway or cable.

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."

The way they wrote it does not change anything there you can still use the 83% just not the table.

 

[don_resqcapt19]

When two code sections conflict which one applies?

Whichever one results in the lowest cost to the contractor

 

[infinity]

It was never intended to apply to NM cable; see post #16. So why the loophole exists currently, it is unwise to use it.

I agree but the current wording would allow NM cable to be used for the feeder in concert with the table. The fact that the 2026 will add wording to not allow this confirms that it is currently allowed.

 

[tortuga]

I agree but the current wording would allow NM cable to be used for the feeder in concert with the table.

I see that took me for a loop the current wording in 334.80 references -> 310.14 then 310.14 references -> 310.15 which references 310.12

The fact that the 2026 will add wording to not allow this confirms that it is currently allowed.

The 2026 wording just says you cant use the table, you can still use the 83%
2026 310.12(B):

(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(A) shall be permitted to be applied for conductors or cables rated 75°C (167°F) or greater.

 

[wwhitney]

I agree but the current wording would allow NM cable to be used for the feeder in concert with the table. The fact that the 2026 will add wording to not allow this confirms that it is currently allowed.

I'm just going to reiterate that whether or not it is currently allowed, using Table 310.12 for any wiring method limited to a 60C ampacity is unwise and improper. The table is obviously based on 75C ampacities.

Cheers, Wayne

 

[infinity]

I'm just going to reiterate that whether or not it is currently allowed, using Table 310.12 for any wiring method limited to a 60C ampacity is unwise and improper. The table is obviously based on 75C ampacities.

Yes, but as you've pointed out many times in the past is that it says what is says or in this case what it doesn't say. It doesn't say you have to use only a 75° C wiring method. The fact that NM cable is still limited to 60° C is dumb but that discussion is for another thread.

 

[wwhitney]

Yes, but as you've pointed out many times in the past is that it says what is says or in this case what it doesn't say.

True, I am conceding that it may be allowed by the wording (have not taken the time to reparse everything carefully). But you still shouldn't do it.

It doesn't say you have to use only a 75° C wiring method.

Correct, but it is obvious in context. Just do the math. : - )

Cheers, Wayne

 

[tortuga]

310.12 has its roots going back the the 1950's as an ampacity adjustment for when there are only 2 CC's on service or feeder, when TW and even type R wire was common. Without a study showing otherwise for 60C wire I see no need to change it.
The mistake that needs correcting in 310.12 is the allowance of 120/208

 

[infinity]

But you still shouldn't do it.

If someone did it wouldn't be unsafe anyway. NM cable has 90° C conductors, SE cable has 90° C conductors. The NEC limits NM to 60° C but allows SE to be used at 75° C. I see no difference from a safety perspective.

 

[tortuga]

So for the 2026 NEC this would be the table for 60C copper conductors used under 310.12;

Service or Feeder rating (Amperes)​	Conductor Copper 60°C​
-​	4​
100​	3​
110​	2​
125​	1​
150​	1/0​
175​	2/0​
175​	3/0​
200​	4/0​
250​	250​
250​	300​
300​	350​
300​	400​
350​	500​
400​	600​

 

[Seven-Delta-FortyOne]

At the end of the day, this setup appears to be on the exterior of the building, which I asked about but the OP has neither confirmed nor denied.

If it is, that negates the use of NM, period.