mc cable

[lmmillican]

I was wondering peoples take on a situation that I noticed. I saw groups of mc cable installed in the bar joist space and covered with spray on insulation. I can't seem to find if this is an approved installation or if there are any derating requirements where the cable is encased in the insulation. Thanks

 

[physis]

Re: mc cable

The only thing I can think of that might say anything about it is 110.10, deteriorating agents. I don't really believe that's a valid argument though, I wouldn't expect the insulation to bother the cable in the least in that regard.

I was thinking about ambient temperature and maybe needing derating but I think the insulation would actually protect the cable from ambient temperature. In the same way that it will try to prevent the heat from getting away from the cables. The heat the cables make isn't ambient though. But whatever temperature they work at might as well be considered the ambient temperature really, cause that's the temperature it'll be around the cable. It's actually worse because there isn't even any convection to help move heat around.

It could be that it's tested to tolerate that kind of environment. The only heat you have to worry about is going to come from the current in the conductors.

 

[bphgravity]

Re: mc cable

The FPN (#3) to section 310.10 cleary indicates that insulation that surrounds or covers conductors effects the temperature rating. What it doesn't tell us is how to determine how much?

 

[ryan_618]

Re: mc cable

According to the NEC, this is only an issue for AC cable. See the change in the 2005 to section 320.80(A).

Notice that this is not in Article 330 for MC cable.

 

[ryan_618]

Re: mc cable

Originally posted by bphgravity:
The FPN (#3) to section 310.10 cleary indicates that insulation that surrounds or covers conductors effects the temperature rating. What it doesn't tell us is how to determine how much?

I don't have a FPN #3 to 310.10.

[ August 22, 2005, 06:15 PM: Message edited by: ryan_618 ]

 

[physis]

Re: mc cable

I got 4 of 'em.

Edit: That's sure a lot of FPN's for one place.

[ August 22, 2005, 06:19 PM: Message edited by: physis ]

 

[ryan_618]

Re: mc cable

No you don't.

Edit...unless you are using a book earlier than the 1996.

[ August 22, 2005, 06:20 PM: Message edited by: ryan_618 ]

 

[physis]

Re: mc cable

Well, it was cool for the few minutes I thought I did.

Edit: It's kind of funny to go to the book to make sure someone's not pullin' my leg and then hardly even look at it. I saw a number.

[ August 22, 2005, 06:24 PM: Message edited by: physis ]

 

[bphgravity]

Re: mc cable

I didn't mean for my post to suggest there are more than one FPN to 310.10. I was indicating it was the third (3) topic in the list to that FPN.

 

[benaround]

Re: mc cable

I would have to agree with Bryan, looks like it could be tagged by Inspector for 310.10

 

[roger]

Re: mc cable

Okay, what if the cables are in close proximity to a metallic roof in mid July in Arizona, wouldn't the insulation work in the conductors favor?

Roger

 

[hardworkingstiff]

Re: mc cable

Originally posted by ryan_618:

Notice that this is not in Article 330 for MC cable.

Do you think that's an "oops" or is there a reason for not including it in the MC section?

 

[LarryFine]

Re: mc cable

Originally posted by hardworkingstiff:

Originally posted by ryan_618:

Notice that this is not in Article 330 for MC cable.

Do you think that's an "oops" or is there a reason for not including it in the MC section?

I vote for "there's a reason".

 

[hardworkingstiff]

Re: mc cable

I would thinks so too Larry, but I would really like to know.... if anyone does care to share.

Thanks.

 

[redfish]

Re: mc cable

</font>

• <font size="2" face="Verdana, Helvetica, sans-serif">II. Installation</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">330.10 Uses Permitted</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">(A) General Uses Type MC cable shall be permitted as follows:</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">(10) In dry locations and embedded in plaster finish on brick or other masonry except in damp or wet locations</font>

<font size="2" face="Verdana, Helvetica, sans-serif">If it is allowed to be embedded in plaster, then I don't see how a little blown insulation would hurt.

 

[physis]

Re: mc cable

Masonry isn't any good at insulating, it's actually a heat sink.

 

[sheldon_ace]

Re: mc cable

Well what about roughing mc or ac in interior walls with insulation? I think that the r value of the insulation, and the actual heat generated by the cable itself together won't be enough to make a difference.

 

[ryan_618]

Re: mc cable

Originally posted by hardworkingstiff:

Originally posted by ryan_618:

Notice that this is not in Article 330 for MC cable.

Do you think that's an "oops" or is there a reason for not including it in the MC section?

I vote for oops. I would bet you will see this addressed in the 2008.