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#186362 - 05/07/09 04:08 PM Old issue  
George Little  Offline
Joined: Jan 2004
Posts: 1,489
Michigan USA
I wonder if someone could comment on the issue of running NM cable in LFNC outdoors. What I see is contractors will run NM cable to an air conditioner disconnect at a residence and then sometimes sleeve the NM cable with EMT for a distance of let's say 5 feet and then terminate the NM cable on the line side of a weatherproof disconnect switch. On the load side of the disconnect they run a short whip, 4 feet or so and install NM cable in LFNC for the final connection. The argument is that the LNMC is used to protect the conductors from liquids, quoting 356.10. What say you?

George Little

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#186363 - 05/07/09 06:14 PM Re: Old issue [Re: George Little]  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Applying "Code Logic," the interior part of the outdoor raceway is still a wet location, so NM is not allowed. Damp location, you say? Still not allowed - I have yet to see a roll of NMC at the parts house; it's all NM-B.

(The 'dry only' limitation in the 2009 can also be used to call into question nearly every crawlspace out there).

Practically speaking? The individual conductors - marked or not - are up to the task. While the code would say 'only if the individual conductor4s are identified as suitable for a wet location, and only if you remove the outer jacket,' in practical terms I don't see the hazard.

If you really want to get their attention, apply conduit fill rules; that will have them running at least 1" raceways! I expect they'll quickly discover junction boxes and jacket strippers.

Likewise, note how the t-stat cable is run .... and have them NOT run it through the power raceways (most will then run it in with the line set).

NM is probably the most confusing wiring method, at least as far as code rules and design is concern. On the one hand, they claim it is safe, and are expanding where it may be used. OTOH, it's considered unsafe, and is the method of choice in defending AFCI requirements. Not only are there the varioua types of NM, there are several wiring methods (UF, SER, etc.) that are very similar, with different rules applied.

#186374 - 05/08/09 12:16 PM Re: Old issue [Re: renosteinke]  
Alan Nadon  Offline
Joined: Mar 2005
Posts: 399
Elkhart, IN. USA
Here's a comment George. The F in LFNC stands for flexible. I have yet to see any NM cable designed to be flexible. Solid conductors will break after too much flexing.
Regarding the thermostat wire it is a violation to run it inside the conduit with line voltage, however I don't remember seeing any thermostat wire listed as sunlight resistant and suitable for outdoor use. Again the flex problem with solid conductors.
There are a number of "we've always done it that way" things that don't really fit with the Code.
I let the elctricians end their work at the outside disconnect and the HVAC guy can make a mess of the rest of it.

If it was easy, anyone could do it.

#186383 - 05/09/09 02:35 PM Re: Old issue [Re: Alan Nadon]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,083
The stat wire is usually tywrapped to the Carflex here, still a violation but not a safety hazard like taking it through the disconnect like you would have to to get it inside the flex.
No they will not let them use RX in the outside wiring, even if they do strip it. If this is new construction the EC runs the RX through the wall to the back of the disconnect and the HVAC installer puts in the whip to the AC with THHN in it.
On a retro fit it is whatever they can get away with. I imagine if the HVAC guy is doing the whole thing it might all be Carflex with THHN/THWN in it since that is what he has on his truck.
If I was doing a retro in one of our 2:12 - 3:12 attics I would fish smurf in the attic (you are not walking around up there), put an LB on the gable end and RNC down to the disconnect, pulling THHN/THWN all the way
I have been away from this for over a decade but when my wife was selling AC systems the permits were pre-approved deals that they just phoned in and inspection was a spotty thing.

Greg Fretwell

#186389 - 05/10/09 07:50 AM Re: Old issue [Re: gfretwell]  
sparky  Offline
Joined: Oct 2000
Posts: 5,308
well why not just run some uf instead...?

and leave one end of the LFNC open, and it's a 'sleeve'


#186396 - 05/10/09 02:23 PM Re: Old issue [Re: sparky]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,083
There is nothing wrong with running UF in a raceway if it is big enough. I suppose it is just what they have on the truck.
HVAC guys usually end up using bigger wire than they have to for that reason, although I doubt most really understand the ramifications of the nameplate rating and the break you can exploit from that. I also see ECs using bigger wire than they need on the line side of the disco but that may be because they don't get to see the actual condenser until it drops ... the day before the closing ... just to be sure it doesn't walk away.

Greg Fretwell

#186400 - 05/10/09 11:06 PM Re: Old issue [Re: gfretwell]  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,830
Brick, NJ USA
Doing inspections on HVAC replacement units is a crapshoot here. The 'regulars' know to check the nameplate; install THHN/THWN from the disco to the unit; strap the flex...and have correct MOCP.

On the other hand...NM in the flex (with/without jacket); t'stat in flex/disco; oversized/undersized MOCP; undersized conductors; blocked disco's....etc.

New const is 95% no issues.

Permits and inspections required for new install and replacements; HVAC by EC only.


#186404 - 05/11/09 02:04 PM Re: Old issue [Re: Alan Nadon]  
SteveFehr  Offline
Joined: Mar 2005
Posts: 1,207
Chesapeake, VA
Originally Posted by Alan Nadon
There are a number of "we've always done it that way" things that don't really fit with the Code.
On the other hand, a lot of the codes have been developed from "we've always done it that way," if "that way" has proven itself to be safe and reliable.

When's the last time any of you saw a failure at an HVAC unit related in any way whatsoever to NM running through LFNC? I can buy the argument that watertight conduit underground is considered to be immersed with a high risk of filling with water and must be treated wet, but watertight boxes are considering dry locations, and homes with siding are considered dry locations, so why not the interior of watertight conduit connecting those two dry locations? If we consider that conduit to be "wet", then what about the "dry" boxes it connects to that all that water will be pouring into? We have to draw the line somewhere. If the code says it's wet through some technicalities, that doesn't necessarily mean it's wet; the code may need revised instead.

Likewise, I can't recall the code offhand, but isn't cable fill N/A or very relaxed for nipples and short runs?

#186408 - 05/11/09 03:07 PM Re: Old issue [Re: SteveFehr]  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,083
Steve, If I was looking for confirmed problems with Romex I would say you could bury it. I see it quite often buried and working fine but "it works" is not the basis for the code.
For that matter I can make a very good case that smurf tube "works" fine outside. I have a piece that sleeves the steering cable on my boat and has held up in the Florida sun for over a decade.

I don't believe "fill" will generally be the issue either. It is just whether RX is listed for wet locations and the answer is no.

Greg Fretwell

#186409 - 05/11/09 03:29 PM Re: Old issue [Re: gfretwell]  
George Little  Offline
Joined: Jan 2004
Posts: 1,489
Michigan USA
I find it interesting that the reason for using LFNC is because it is cheap and easy to install. I don't think the reason is for vibration or that we need the flexibility for anything other than ease of installation. Alan made an interesting comment regarding using stranded conductors to accommodate the installations need to flex. I also mentioned in my post the fact that often times we see NM-B cable installed in EMT, which is certainly not water tight because no one uses the fittings suitable for making it water tight. I think we were better off with NM cable that had TW conductors in it instead of the THHN conductors found now it NM-B. I guess we are more concerned with heat now and most of us agree that the wet location should be avoided with NM-B. THHN is suitable for a dry or damp location so maybe that's where it should be used. Outside is a wet location and we should be using a wiring method that is suitable for a wet location.

George Little

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