Proposed NM Cable ampacity in WA State

tom baker

tom baker

First Chief Moderator & NEC Expert
Staff member
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Bremerton, Washington
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Master Electrician
WA labor and industries has a proposal to change NM-B ampacity for 8 and larger to be the 75 deg C rating in WAC 296-46B. Pubic comments will be accepted Oct 7 and the final rule will be issued Dec 19
It will be interesting to see comments but there are likely many EV charging stations on 8 NMB at 60 amps
Link https://lni.wa.gov/licensing-permits/_docs/Draft-Rule-Language-Version1.pdf
Advantage is for 6 NM-B on a 60 amp circuit for EVS. 1756166999240.png
 
I don’t know. WA labor and industries are pretty sharp on the NEC with many rules to fix the NEC. I will make a public comment in Oct to see the re see the response
 
Maybe the question is why has NEC kept NM and UF cable restricted to 60C even though they have contained 90C conductors for about 40 years now and they do let you use 90C for ampacity adjustments?
 
kwired said:
Maybe the question is why has NEC kept NM and UF cable restricted to 60C even though they have contained 90C conductors for about 40 years now and they do let you use 90C for ampacity adjustments?
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The question is why limit it at all? If you're writing a local code amendment just make it for all sizes of NM cable.
 
kwired said:
Maybe the question is why has NEC kept NM and UF cable restricted to 60C even though they have contained 90C conductors for about 40 years now and they do let you use 90C for ampacity adjustments?
Click to expand...
My guess is because of how they are used in residential applications, buried in insulation, etc.
 
infinity said:
The question is why limit it at all? If you're writing a local code amendment just make it for all sizes of NM cable.
Click to expand...
Given 240.4(D), the utility of extending the change to smaller than #8 is more limited. So perhaps it is seen as less rocking of the boat to only make the change for larger conductors.

FWIW, 338.10(B)(4) similarly imposes a distinction on SE cable with #10 and smaller versus #8 and larger.

Cheers, Wayne
 
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