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Advice on wiring run, please

Posted by kudzu9 (My Page) on
Tue, Dec 10, 13 at 3:50

I am installing a bathroom in the corner of a 20' X 20' finished room. I have a more than adequate size subpanel in the room, and it is located about 15' away from where I need to run new cables to. The room has a cathedral ceiling and a concrete slab floor, so I have no basement or attic to run cable through.

The run would be along a single, exterior wall. If I have to tear out 15' of sheetrock horizontally, I will, but I'm also wondering if it is code compliant to do the following:
1. Run the cables inside the wall from the subpanel down to near floor level, and then take them to the exterior of the wall through a conduit body.
2. Run them from the conduit body through 15' of conduit on the outside of the wall,
3. Then bring them back inside the wall through a second conduit body.

The three cables I need to run are two 8/2 and one 12/2, both NM-B.

Any advice, besides whether this is code-compliant, will be welcomed. Thanks.


Follow-Up Postings:

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RE: Advice on wiring run, please

You need two 8/2's for a bathroom?

You have a problem with conduit (in addition to making the outside of the house ugly). You shouldn't be running NM through conduit (except for short sections for physical protection). Even if you run individual conductors (THHN or whatever) through the conduit, you are going to have to derate them because you now have more than three current carrying conductors in the conduit.


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RE: Advice on wiring run, please

To make horizontal runs in finished walls, it usually is sufficient to just make a handhole on each side of each stud. In some cases, it is possible to open the wall at only every other stud if the D'versiBit or similar drill system is used.


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RE: Advice on wiring run, please

The other hack, depending on how the house is sided, is possibly to pop a course of siding off to get access to run the cable.


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RE: Advice on wiring run, please

ronnatalie-
This is a guest bathroom which will only be used several times a year. The pair of 8/2's are required for a tankless water heater. The side of the house where I would put an exterior run is hidden from view by evergreen bushes, so I'm not worried about having to view the ugly conduit. And I appreciate your suggestion about the siding...however mine is cement board vertically applied so that's a no go. I'm not going to run individual conductors, so I'm curious: Is this idea of mine a non-option code-wise due to the derating issue, even though I would have only about a 15' run?

bus_driver-
Thanks for your tip. If I have to cut into the sheetrock, that will minimize the repair work.

Everyone-
Lastly, I just had one other idea that I'd like comments on. The baseboard molding for the room is about 4-1/2" high. Can I remove the molding, cut out the bottom 4" of sheetrock, notch out the edges of the 2X6 joists a bit and run the cables behind the baseboard? I would install a steel nail protection strip all along the run, and then reinstall the sheetrock and trim. That way, no sheetrock patches would be required.


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RE: Advice on wiring run, please

Yes, you must derate the cables which probably means going up in size on the tankless wiring depending on what it actually draws. Six current conducting wires needs to be derated 80% (yes over 15'). Your 12-2 is probably OK because NM has a quirk in that it uses the 90 degree column for derating purposes.

Nothing wrong with running behind the baseboards. Notching may be structurally problematic. You can certainly bore holes down that low.


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RE: Advice on wiring run, please

Thanks, ronnatalie-
I'm always glad to see you join in a discussion because you clearly know your stuff and are able to communicate it in such a clear and concise manner.


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RE: Advice on wiring run, please

Cables not in conduit must be derated? Code reference please.


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RE: Advice on wiring run, please

Cables not in conduit must be derated? Code reference please.

I didn't say that. I said he has to derate it because there are more than three (he has SIX) current carrying conductors in the conduit.


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RE: Advice on wiring run, please

"Posted by ronnatalie (My Page) on
Tue, Dec 10, 13 at 15:32

Yes, you must derate the cables which probably means going up in size on the tankless wiring depending on what it actually draws."

"I didn't say that."

Res ipsa loquitur.

As I understood it, the conduit was proposed as a means of running the wiring on the exterior of the building. Agreed that this would be considered an unattractive addition. Another possibility would be to bury the wiring method, perhaps UF cable, with only the risers and wall penetrations showing on the exterior--- still not at all attractive. But it often is helpful to first identify all the possibilities and then eliminate all the ones that are most objectionable.


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RE: Advice on wiring run, please

You deleted the following sentence: Six current conducting wires needs to be derated 80% (yes over 15').
where I explain why and in my first post I specifically said that it was because it as more than three.


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RE: Advice on wiring run, please

"Yes, you must derate the cables which probably means going up in size on the tankless wiring depending on what it actually draws. Six current conducting wires needs to be derated 80% (yes over 15')."
Code reference please for requirements for derating cables? What is the spacing required by 310.15(B)(3)(a)?


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RE: Advice on wiring run, please

You obviously know where to find the requirement. He has six current carrying conductors, that's more than three in a RACEWAY. 310.15(B)(3)(a) applies. The minimum spacing wording in that doesn't apply because the second half of that clause says "and are not installed in raceways."

If you have more than three current carrying conductors in a conduit, be they individual conductors or inside cable (which is then inside the conduit) you must derate them.


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RE: Advice on wiring run, please

The discussion is about CABLES, not conductors in conduit. As far as I know that possibility is not being considered at the moment. I do agree about the derating of conductors in CONDUIT. The cutting of hand holes is to install CABLES as I know of no way to install conduit through the hand holes, not even ENT, of sufficient size to accommodate all the conductors required.

""Yes, you must derate the cables" CABLES!!!

This is the part that raises the question that is my concern at the moment.


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RE: Advice on wiring run, please

What are you talking about BUS? He's talking about running it through 15' of conduit on the outside of his house.

I'm addressing his plan not the suggestion we made to install the wire through the drywall. In every darn post I made I made it clear I was talking about his conduit plan. The original poster seems to understand what I'm talking about even though you have your head somewhere else.


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RE: Advice on wiring run, please

Another possibility is to use a small soffit in the room to conceal the cables at the intersection of the ceiling and the walls. Crown molding added to the soffit would improve the appearance. It could be installed around the room for consistency.
This is not a great solution-- but none of the identified options are especially good. Sometimes none of the options are good ones.


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RE: Advice on wiring run, please

bus_driver-
Thanks for the additional suggestion, which I'll keep in my bag of tricks for future work. Unfortunately, this won't work in this situation as the room has a peaked ceiling rising from 8.5' in the corners to about 14' in the center along that wall and crown molding wouldn't look good.
I've given up on the outside conduit idea, and will either take out some sheetrock and drill into the studs, or remove the baseboard and run the wires behind it. Once I start getting into it I may be back for some more advice. Thanks for the help so far.


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