NEC '08 (334.80) Ampacity

Magnettica

I just got a great deal on the 'Significant Changes to the NEC 2008' book and today it came in the mail. I paid a whole $3.65 + $3.00 shipping and handling so great deal there. Anyway, one of things I noticed in 334.80 is the new requirement for derating 2 romex cables stapled together that will now have to be derated where they'll be in direct contact with insulation. The new rule (in paragraph 3) makes sense but how on earth will the AHJ or EI possibly enforce this?

waysides

Great deal...........e-bay

waysides

Hopefully before the sheetrock goes up........maybe Superman and x-ray vision

Magnettica

Actually, Amazon.

They must have made an error when posting the price. This book sells for nearly $70 at Barnes and Noble.

Celtic

Mags..I'm going to take a "wait and see" stance on this [as well as AFCI].

NJ has yet to accept the '08 and the final amended version has yet to be released.


EDIT:
"Rumor" has it that tom'row [2-20-09] the '08 becomes "law".

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Magnettica

Well thanks for the update. I know u posted the link for all the state amendments before but if it's not any trouble could post it again?

Thanks.

Celtic

Negative Ghostrider.


I saw your post and I went to the proposals myself...334.80 does not "appear" on the list...that is not to say it won't show up in the final draft

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Bubbles

So I guess if you run 2 - 10/2's together (not sure why you would...dryer cir.) then that's breaking the rule I'm guessing? What's the derating? too tired to look

Bubbles

I meant 10/3's before anyone rips me a new #^%hole on here..lol

Bubbles

I think it's 3 or more mag. Just looked it up anyhow. Guy got me Jan 2nd on this. Really didn't think they would push that one. Think I had 3-12/2's together but one was an 1800 watt Microwave. With the derating I think it made it 1 amp over or something trivial. Oh well! I think it's greater than a 24" run as well too??

Magnettica

I think you're right. I misread something, imagine that!

It says.... paragraph three...

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, he allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15 (B)(2)(A).

So if I did this...



...on an outside wall or where there'll be insulation installed, each conductor within each cable will have to be derated.

Bubbles

It's getting a little crazy. I'm not saying de-rating makes no sense but, so that means we might have to start running 8-3 for Dryers and 10-2 for Microwaves maybe?? Never knew about derating each cable in insulated wall. Good heads ups. I'm glad I got out of new houses a couple years ago. I bet #$%^ is hitting the fan for folks on the 08' code. I work in 5 different counties (3 on 05' and 2 on 08'). And some cities in county that has 08' is 05' and vise verse. I have to always stop and think were I'm at first. It's confusing the hell out of me! lol

TinkerGA

I may be wrong but I think the thermal insulation is the romex outer sheath,not wall insulation.

480sparky

If that's the case, then all NM has two CCCs in contact with thermal insualtion, and must be derated.

Reread it. It states, in part, ".....without maintaining spacing between the cables.....". If the sheath is thermal insulation, then that part makes no sense.

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JohnJ0906

Keep in mind, the derateing will be done from the 90° column. Chances are, for smaller sizes, this will have no effect practically speaking.

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John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC

Eddy Current

Here's a few Canadian codes concerning romex to compare.

-If wires are run in contact with each other (like with a tie wrap etc.) for distances exceeding 600mm (2 feet) they must be de-rated
-Only one wire per staple!
-The staple used must be rated to support the size of wire.

I used a few 2" PVC straps once to clean up my wires as they came down the wall and into the side of the panel and the inspector made me remove them and staple each wire individually! Looked much better the way I did it but the wires were in contact with each other for more than 2".