2008 and derating

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480sparky

Senior Member
Location
Iowegia
Here it the same paragraph:

334.80: Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insluation without maintaining spacing between cables, the allowable ampacity of each conductor whall be adjusted in accordance with Table 310.15(B)(2)(a).
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Cavie said:
Where can I read about derating in the NEC 2008 amd how it will pertain to NM and attics?

334.80 Ampacity. (new last paraghaph)

Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).

Good morning Cavie. Do you derate NM in attics?
 

walkerj

Senior Member
Location
Baton Rouge
All I see is thermal insultion, nothing about attics. Although I know it cn get into the 150's or 160's in attics round here, at least. Same in Florida
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
chris kennedy said:
Drats, You know how long it took me to type that?

It's much easier to tell them where to find it. :wink: :smile:

Roger
 

480sparky

Senior Member
Location
Iowegia
walkerj said:
All I see is thermal insultion, nothing about attics. Although I know it cn get into the 150's or 160's in attics round here, at least. Same in Florida

What do you think 'thermal insulation' is? Polyisocyanurate. Fiberglass. Rock Wool. Slag Wool. Mineral Wool. Cotton/Denim. Cellulose. Polyurethane. Styrofoam. The 'thermal' means the purpose of the insulation... to prevent the transfer of heat.. You put insulation in your attic to reduce heat loss in the winter and heat gain in the summer. They probably threw the term 'thermal' in because someone would confuse it with the insulation on a wire

Now I can see someone arguing with an inspector about insulation that is installed for sound control purposes not being 'thermal'.

roger said:
It's much easier to tell them where to find it. :wink: :smile:

Roger

Not everyone has a 2008 yet.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
480sparky said:
Now I can see someone arguing with an inspector about insulation that is installed for sound control purposes not being 'thermal'.
I like that. Tell the inspector I insulated the attic so I don't here the rats.

I have never heard of an inspector asking for this derating. The MN is normally run on the sides of trusses putting it mostly under the insulation.(I think) So the 140 deg. rating would not be exceeded. IMO
 

480sparky

Senior Member
Location
Iowegia
chris kennedy said:
I like that. Tell the inspector I insulated the attic so I don't here the rats.

I have never heard of an inspector asking for this derating. The MN is normally run on the sides of trusses putting it mostly under the insulation.(I think) So the 140 deg. rating would not be exceeded. IMO

I don't put it on the side unless I'm running parallel to it. If I run it perpendicular, it sits on the top edge. And I know that some attics, even here in the midwest, can get up to 140-150?F, but most of the NM is below the bulk of the insulation, and the temps there are much more reasonable. Now I can see that argument coming into play as well, so maybe the '11 will have some sort of 'sliding scale' for derating, based on where in the insulation it is.

Chirs, as for sound control, just tell the inspector you installed insualtion in your attic to prevent the sound of overhead airplanes from disturbing you.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If it's under the insulation the air around it is likely very close to the temperature of the ceiling below it. In which case ambient temperature correction wouldn't even matter.
 

bphgravity

Senior Member
Location
Florida
Cavie,

The Gulf Coast Division will be having a 2008 Code Change Seminar in February. I will send you a flyer and registration. Mark Ode will be doing the main presentation, however I am also in the works to get a representative from the Copper Development Association to give a session on new requirements for derating (adjustments and corrections) due to ambient temperature, rooftop installations, NM cable installed with insulation, ect.

I recently took the course at the Southern Section Meeting. I you would like details, let me know.
 

Cavie

Senior Member
Location
SW Florida
chris kennedy said:
I have never heard of an inspector asking for this derating. The MN is normally run on the sides of trusses putting it mostly under the insulation.(I think) So the 140 deg. rating would not be exceeded. IMO

We don't ask for derating. It is just being kicked around our office as none of us have the 2008 yet. IAEI mag articals seems to sugest derating in 2008. As for your putting the romex on sides of trusses. Let me see. Blown in = rx in the insulation. Battens nailed to the bottom of trusses = rx in the insulation. You know somthing I don't??:-?
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Cavie said:
We don't ask for derating. It is just being kicked around our office as none of us have the 2008 yet. IAEI mag articals seems to sugest derating in 2008. As for your putting the romex on sides of trusses. Let me see. Blown in = rx in the insulation. Battens nailed to the bottom of trusses = rx in the insulation. You know somthing I don't??:-?
Thats why my statement was followed by (I think). It's questionable at best.
Never heard of any sort of problems with NM in attics. So heck, lets just go ahead and derate anyway. Should be loads of fun.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Now that the practice of two MN's under one staple is over so we can maintain spacing, what will be acceptable spacing?
 
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