Type NM cable and Article 440

[infinity]

I've seen conflicting opinions on where or not type NM cable, when used to feed an AC unit covered under article 440, that it is required to be sized at 60 degrees Celsius? 334.80 states: 'The ampacity shall be in accordance with the 60 degree Celsius conductor rating'. I see no exception for conductors feeding AC units so I'm assuming that if I use Romex to feed an AC unit I can only use the 60 degree ampacity. Any comments?

 

[charlie]

Re: Type NM cable and Article 440

That is exactly what the Code means. It does seem to me that most residential ACs will run at around 17 to 19 amperes so a #12 Cu. NM cable on a 40 ampere circuit breaker is the normal installation.

 

[augie47]

Re: Type NM cable and Article 440

ahh! but if this ac unit is outdoors....

the plot thickens

 

[infinity]

Re: Type NM cable and Article 440

My original post was considering an outdoor unit with the compressor and fan. Don't tell me that the plot thickens because this is a wet location and NM isn't allowed.

 

[bphgravity]

Re: Type NM cable and Article 440

NM should not be installed in the whip from the disconnect to the unit itself, but I don't have a problem with the NM being chased through the wall to the outside.

 

[charlie]

Re: Type NM cable and Article 440

Thanks Bryan, my sentiments exactly.

 

[infinity]

Re: Type NM cable and Article 440

Yes, thanks Brian and Charlie. I felt one of those type NM into the back of the disconnect is a wet location 100 post threads.

 

[charlie]

Re: Type NM cable and Article 440

It can be a wet or damp location if it is not sealed properly. It is no different than a type NM that is stubbed out for an outside light, its just a little larger in most cases (most people will run a #10 instead of a #12).

 

[mvannevel]

Re: Type NM cable and Article 440

Just out of curiosity, why would NM not be allowed in the whip from the disconnect to the unit? Let's just assume the whip is LFMC.

 

[George Stolz]

Re: Type NM cable and Article 440

Originally posted by mvannevel:
Just out of curiosity, why would NM not be allowed in the whip from the disconnect to the unit? Let's just assume the whip is LFMC.

Originally posted by infinity:
...because this is a wet location and NM isn't allowed.

See (NEC-2002) 334.12(A)(10)(d): NM is not permitted where subjected to excessive moisture or dampness.

See 310.8.

 

[mvannevel]

Re: Type NM cable and Article 440

Why would the interior of a liquid tight conduit with listed fittings and properly installed be a wet location, or subject the NM to "excessive moisture or dampness? If the conduit were installed underground, I could see it being a wet location. But a 3' whip to the unit, I'm not so sure. Myself, I'd rather use THHN from the disconnect to the unit but I don't see the NM as a violation.

 

[George Stolz]

Re: Type NM cable and Article 440

Originally posted by mvannevel:
Why would the interior of a liquid tight conduit with listed fittings and properly installed be a wet location, or subject the NM to "excessive moisture or dampness? If the conduit were installed underground, I could see it being a wet location. But a 3' whip to the unit, I'm not so sure. Myself, I'd rather use THHN from the disconnect to the unit but I don't see the NM as a violation.

THHN wouldn't be okay either, by the definition of "Wet Location."

(NEC-2002) Article 100: Location, Wet. Installations under ground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.

So, the A/C is sitting in a wet location.

Now your argument is that the inside of the conduit is not; but there's a problem. Look at 310.8, it makes clear what conductors you can install in conduits in damp locations, and wet locations. NM cable didn't make the list. Neither did THHN.

As far as the NEC is concerned, the conductors inside of your conduit need to be as tough against moisture as the conduit itself. And sitting outside is considered a wet location, even where it is not exposed to saturation.

 

[infinity]

Re: Type NM cable and Article 440

George,

The inside of LFMC above ground is not a wet location.

 

[mvannevel]

Re: Type NM cable and Article 440

I have to agree with infinity, the interior of the LFMC above ground doesn't meet the definition of wet location. And, installed above ground, you couldn't even call it a damp location.

 

[iwire]

Re: Type NM cable and Article 440

Playing the devils advocate here.

 

[George Stolz]

Re: Type NM cable and Article 440

Then what does 310.8(C)(2) represent? You wouldn't run THWN without a raceway, would you? And all outdoor installations of raceways must be suitable for the location, per 300.6.

The area is a wet location: look at 406.8(A):

...A receptacle shall be considered to be in a location protected from the weather where located under roofed open porches, canopies, marquees, and the like, and will not be subjected to a beating rain or water runoff.

"Protected from the weather" involves structural outcroppings, not wiring methods. The in-use cover is installed in a wet location, that doesn't cause the receptacle to be in a dry location--it's a receptacle installed in a wet location with provisions for it's location.

The LFMC is installed in a wet location, by the definition of a "Wet Location"; the A/C unit is sitting out in the weather. 310.8(A)(2) kicks in to tell us what conductors to install in that conduit.

 

[iwire]

Re: Type NM cable and Article 440

Originally posted by georgestolz:
The LFMC is installed in a wet location, by the definition of a "Wet Location"; the A/C unit is sitting out in the weather. 310.8(A)(2) kicks in to tell us what conductors to install in that conduit.

I am really having some fun now, I can argue the other side now.


I follow you George but then I also have to ask if an any raceway used outside is always a wet location why in Article 348 do they need to specifically tell us that FMC can be used in wet locations if used with wet location conductors?

That is redundant.

 

[iwire]

Re: Type NM cable and Article 440

George please go back a page to check out my post.

Bob

 

[iwire]

Re: Type NM cable and Article 440

Originally posted by georgestolz:
The in-use cover is installed in a wet location, that doesn't cause the receptacle to be in a dry location--it's a receptacle installed in a wet location with provisions for it's location.

You may want to rephrase that as there are not any duplex receptacles listed for wet locations.

If the wiring method does not provide a dry location you can't install the device.

BTW, this applies to breakers in outdoor enclosures.

 

[George Stolz]

Re: Type NM cable and Article 440

Bob wrote:
George please go back a page to check out my post.

Good call, you snuck in there on me.

Originally posted by iwire:
When was the last time you saw LFMC between a disconnect and the machine it feeds 'arranged to drain'?

All the time! Water will run out the A/C unit like a sieve, there's no gasket on it.

As for the receptacle bit, maybe I need to mull this over some more. I think you're right, it backfired.