SE/NM Ampacity confusion MA code

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electricmanscott

electricmanscott

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Boston, MA
I am somewhat confused.

338.10B(4)a Tells me that for interior installations SE cable must comply with part 2 of 334. Under 334.80 NM ampacity shall be in accordance with 60 degree temp rating. This would say that interior se and nm shall be sized to the 60 degree column of table 310.16

Massachusetts amends 334.80 as follows...

Delete the second paragraph and revise the first paragraph to read as follows:
334.80 Ampacity Type NM, NMC, and NMS cable shall have conductors rated at 90c. Where installed in thermal insulation, the ampacity of conductors shall be that of 60c conductors.


So with that amendment, if SE or NM is not installed in thermal insulation I would size according to the terminal rating of the equipment I am connecting to. I believe that in most cases this would be a 75c rating therefore #8 NM can be protected at 50 amps.

Also for a 100 amp sub panel I would have to use #1 AL sized at 75c


Am I off track here?
 
Scott
I agree with your post. You may load the NM and SE to 75 deg as long as not in thermal insulation. I've addressed this with MA CMP members and a few were suprised. It will be intersting to see what 2011 brings.
 
I think the NEC 2011is looking at wording 338 just as MA. has done. Basically it says to use it as we have been unless it is run thru insulation. I assume they also mean fire caulking etc, but it doesn't appear to state that.
 
Dennis that is partly where I was going with this. I have seen the 2011 change and it is the same as MA. My question would be what does installed in thermal insulation mean? Almost anything run in a dwelling here would go through insulation at some point. Even if its just passing throught from upstairs, through the insulation in the basement ceiling, to the panel. Does that 10" of insualtion count?
 
cpal said:
I'm guessing it will.
Click to expand...
So am I? It is hard to imagine going thru fiberglass would be a problem. Perhaps they are anticipating the spray in foam, fire caulking etc. How that little bit of insulation can cause issues I am not sure.
 
I sure hope they revise the revised code on this one....The insulation clause would be asinine....In most cases on useing SER cable for services, it runs through some sort of insulation..:confused:
 
gotmud said:
I sure hope they revise the revised code on this one....The insulation clause would be asinine....In most cases on useing SER cable for services, it runs through some sort of insulation..:confused:
Click to expand...
I believe the 2011 proposal is similar to the MA amendment "where run thru insulation"
 
Perhaps 310.15(A)(2) Exception could be used for intermittent contact with insulation to maintain the ampacity at the 75 degree rating.

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

Pete
 
pete m. said:
Perhaps 310.15(A)(2) Exception could be used for intermittent contact with insulation to maintain the ampacity at the 75 degree rating.

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

Pete
Click to expand...


I think it should but I don not think the CMPs would agree. I do not think they let us use that when a few NMs pass through a caulked hole.
 
I just installed a sub panel for an addition I'm working on. I ran 1/0 AL ser because of the insulation factor. About 10' will be in insulation. In reality 100 amps was way more than needed but I specd it in the proposal so I had to do it.

At the same time the HVAC's electrical sub ran a 100 amp sub panel. Guess what size AL SER he ran? Think 310.15-B6 Also the receptacle on th AHU is not GFCI protected.

I will be sparky snitch when the inspector comes for the final inspection. :roll:
 
Good point Bob.

Although, if the change to 338.10(B)(4)(A) is accepted as worded then 334.80 won't be a "player" with regards to using SE cable as a branch circuit or feeder wiring method. Of course, this is only if the verbiage is adopted as proposed.

I wonder if MA will embrace this change?

Pete
 
pete m. said:
Good point Bob.

Although, if the change to 338.10(B)(4)(A) is accepted as worded then 334.80 won't be a "player" with regards to using SE cable as a branch circuit or feeder wiring method. Of course, this is only if the verbiage is adopted as proposed.

I wonder if MA will embrace this change?

Pete
Click to expand...

the ma amendment to 334.80 very generous when the NEC language is considered.
 
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