6/3 w-ground

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1793

1793

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Table 310.16 #6 CU @ 75deg = 65 amps.

Would Article 334.80 come into play for 6/3 w-ground, @ 60deg. only good for 55 amps, to feed a sub-panel in the same structure?
 
Looks like it. That's a new one on me. Why ??? I don't know. At least you can fuse it at 60 amp if the load is not greater than the 55amp.
 
Dennis Alwon said:
Looks like it. That's a new one on me. Why ??? I don't know. At least you can fuse it at 60 amp if the load is not greater than the 55amp.
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I was also looking for the information in 240.6, which I found, while looking around 240.4.
 
Norb- I think I know why you use the 60 degree rating for romex. I believe the jacket of romex is only rated for 60 degrees. I remember this from a long time ago. It may not be in the NEC other than your reference art. 334.80
 
It says 90 degrees on the jacket. If it weren't for 334.80 we could use it with the 90 degree rating in mind.

IMO, they likely have that limitation right off the bat in order to just not get the NM as big a workout as other wiring methods, due to it's lesser reputation and where it's generally installed.
 
There doesn't seem to be much difference between NM and SE R, but I haven't seen any restriction on using SE R at the 75 C rating. Given the higher temperature rating, it seems like there is no reason to use the NM for cases where the SE R is available.

For example, you can get SE R in 2 2 2 4 aluminum which is rated at 90 Amps at 75 C, but the same wire at 60 C would be only 75 Amps.

338.10(B)(4)(a) excludes SE from the 334.80 Ampacity provisions that apply to NM.

Am I missing something?
 
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georgestolz said:
It says 90 degrees on the jacket. If it weren't for 334.80 we could use it with the 90 degree rating in mind.

IMO, they likely have that limitation right off the bat in order to just not get the NM as big a workout as other wiring methods, due to it's lesser reputation and where it's generally installed.
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I am not doubting your claim but the 14/2 wire I have in my basement (brand new) made by encore wire (http://www.encorewire.com) does not have a temp. rating nor does its website give any info for its jacket. Puzzled!!!
 
dcspector said:
110.14(C) termination provisions......? I thought 334.80 was for derating.
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It is for derating also but the second sentence in article 334.80 states "The ampacity shall be in accordance with the 60 degree C conductor temperature rating".

Say for instance you have so many bundles of 8/2 copper that you need to derate, you can use the 90 degree rating to derate but you still cannot go over the 60 degree rating for your circuit. Thus #8 copper would only be good for 40 amps. Of course, you can fuse higher under certain conditions such as A/C loads, etc.

Under the same conditions #6 copper would be good for 55 amps but you can go to the next standard size breaker-- thus a 60 amp CB is legal. This is providing the derating doesn't fall lower than the 60 degree C.
 
1793 said:
I would think we could use the 75deg column in Table 310.16, 50amps, if the termination points were rated for 75deg.
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Since there is no limitation on SER or SEU (why???) then I agree 50 amps at 75 degree for #6 alum. Assuming the breakers are rated 75 degree. I know ( I am always wrong when I say I Know) , I believe that the old breakers were rated 60 and the new ones are 75 rated
 
Dennis Alwon said:
I am not doubting your claim but the 14/2 wire I have in my basement (brand new) made by encore wire (http://www.encorewire.com) does not have a temp. rating nor does its website give any info for its jacket. Puzzled!!!
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Well, 334.112 requires the NM to be manufactured with 90 degree insulation, maybe they decided they were wasting ink confirming it? :)

I don't know why SE cable is excluded from 334.80, I'm sure there is a reason, it might be in recent ROPs. :)
 
Dennis Alwon said:
I am not doubting your claim but the 14/2 wire I have in my basement (brand new) made by encore wire (http://www.encorewire.com) does not have a temp. rating nor does its website give any info for its jacket. Puzzled!!!
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Is this wire marked NM or NM-B? Type NM wire is rated at 60C. Type NM-B is rated for 90C.
 
georgestolz said:
Well, 334.112 requires the NM to be manufactured with 90 degree insulation,
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I believe that article is referring to the conductor insulation not the jacket insulation.

And yes this is NM-B.

Of course, all of this is really a moot point since art. 334.80 requires one to use the 60 degree rating. I was just curious where the 90 degree rating comes from. I know when romex first came out the jacket was 60 degree. They must have changed that. The wire I am using has plenty of markings but no temperature rating
 
JohnJ0906 said:
Romex is constructed from 90 deg conductors. AS AN ASSEMBY it is treated as a 60 deg.
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Yes we know that but "why" was the question. I thought it was because the jacket was only rated 60 degree but I think I am being told that the jacket is rated 90. If that is the case why the rule to treat romex at 60.
 
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