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?

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.

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.
Alan

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.

well why not just run some uf instead...?

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

~S~

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.

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.

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?

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.

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.

I haven't seen THHN that wasn't also THWN labled, at least not since I can remember.
I assume manufacturing expediency probably makes the conductor in NM-b the same wire, without the marking. Unfortunately that keeps us from ensuring compliance so we are obligated to fail it or 90-4 it.
I believe the paper packing is probably why NM is not OK in wet/damp locations.

A telling thing is when I search "wire" manufacturer sites for NM-c I get UF.

I just read Article 334 on NM cable and it's starting to become clear to me that NM cable or more properly identified as NM-B is only suitable for interior wiring. It specifically mentions "in" buildings or structures. Not even suitable for damp location. Dry locations only. I'm not willing to say that the inside of LFNC is dry. Might not be wet but for sure damp. NM cable is a no no for use outside the building. There I said it. So let it be written- So let it be done.

The ban on NM in damp locations is new - and, as far as I'm concerned, absurd. Eveb the older cloth-wrapped version worked just fine in such 'damp' locations as crawl spaces and under decks.

"NMC" differs from plain "NM" in being 'corrosion resistant.' For the life of me, I cannot see how the current PVC jacket is not 'corrosion resistant.' Having actually done the relevant tests, I have no doubt it would pass. So why isn't the common product marked "NMC-B?" Only Southwire knows for sure.

That an inquire would be referred to UF is silly; UF has it's own code section.

Ditto for the practice of using unmarked wires inside the jacket. Why? If the manufacturers are using this practice to limit the use of their product, let's just change the code to ban it, marked or not.

The NEC seems - and I've said this before - a bit bi-polar regarding NM. Some recent changes (expanded list of approved occupancies) suggest it's a reliable, proven, safe method; others (damp location ban, AFCI's) suggest it's the 'tobacco' of the trade.

Getting back to 'where the rubber meets the road,' we have to make the judgement call: just where is the problem? If the conductors are otherwise proper, where's the introduced hazard?

The same approach applies as well to the running of the t-stat wire. Why not run it with the power wires? The t-stat wire I see is rated at least 150 volts - more than either power conductor to ground. Most has a 300 volt jacket. Wouldn't you rather see the wire in the power conduit, than encased in the foam insulation of the very hot line set?

The hazard with the t-stat wire in the same raceway with the power is not the wires but what they are connected to. A failure of one system to the other could put 120 V to the thermostat. That could be a real surprise.

You need TWO failures to get 120 V to the thermostat. Failure of the line voltage insulation PLUS the failure of the T-Stat insulation.

Larry C

Reno, I still believe it is the paper packing in RX that is not water friendly. It might wick water into boxes etc.
That seems to be the concern when you read the "flooded house" articles. Maybe someone has a link to the NOLA article in IAEI News.
As far as I can determine, NM-C is NM with a plastic packing instead of paper. I have never actually seen any NM-C and I do not think Southwire really makes it, hence routing me to UF when I try to look it up (assuming I want to buy a pallet I guess).

In regards to UF/NMC, I found this on Southwire's website:

"Southwire Type UF-B cable is generally used as feeder to outside post lamps, pumps, and other loads or apparatus fed from a distribution point in an existing building as specified in the National Electrical Code1. UF-B cable may be used underground, including direct burial. Multiple conductor UF-B cable may be used for interior branch circuit wiring in residential or agricultural buildings at conductor temperatures not to exceed 90°C (with ampacity limited to that for 60°C conductors) as specified by the National Electrical Code. UF-B can be used in applications permitted for NMC in Section 334.10(B) of the National Electrical Code. Voltage rating for UF-B cable is 600 volts."