Electrical question: conduit and wiring

[Alan Tolchinsky]

Hi All, I'm about to relocate to a garage shop and have a question concerning EMT type conduit and NM 12/3 wire. Can you use this type wire inside metal conduit or do you have to use the separate wires? I've seen where people have done this in some situations but is there a problem with it? Thanks.

[James A. Wolfe]

Alan,
Talk about your loaded question.... The answer may depend on where you live and the code followed in your area. Based on the NEC there are at least two references concerning NM cable and EMT. Article 334-15(b) says that NM cable may be installed in EMT where required for physical protection. Article 373-5(c) is an exception to placing multiple NM cables in solid raceways connected to panels. Short answer (as if there ever was a short answer when talking about the NEC) if you're just using the conduit to protect the NM cable, you're OK. All the restrictions for NM cable remain in effect such as wet locations, GFCI etc.

More appropriately, why would you want to run NM in conduit anyway? The cable is tough to pull and the jacket can get cut in fittings and it's generally not worth the extra trouble if you're going to run conduit anyway. Just curious.

Jim

[Jim Becker]

I have used it to "protect" the NM as Jim mentions in my shop as I have installed electrical drops down the wall. (The NM cannot be left exposed and this was always retrofit work as I changed things around in the shop) But I also agree with his last comment...I wouldn't want to pull this stuff through conduit for any kind of distance or around bends. Using the proper loose conductors is so much easier and you can always transition to NM in a J-box where needed and appropriate.

[Steve Cox]

Or better yet, why not use MC cable. This is flexible conduit with the conductors already inside. Allowed by the NEC for surface mount.

[Dev Emch]

Personally, I would not. I could get into a diatribe or wind up being a boviator as ORielly calls them. I use EMT all the time and I see no need to stuff 12/3 into a conduit. Secondly, pulling a 12/3 safely through an EMT conduit may be very difficult resulting in damage to the wire. Why cann't you use THHN? That is my favorate wire!

[Phil Maddox]

When you install mn cable inside of conduit, it de-rates the conductors. The jacket is the wrong material, and the conductors are not as flexible as they should be. If the inspector is on top of things, it should not pass code.

That being said, I've seen it done many times and it fact have it done this way for the AC unit for my shop. I needed some protection so I ran the romex in conduit for about 4'.

Good luck.

[Charlie Knauer]

Alan, Codewise there is no problem running 12/3 inside emt. Derating is not an issue with 1 or 2 cables. As Dev stated using type THHN wire inside of the conduit is easier and more practicle. What area of Maryland are you located?

Charlie

[Alan Tolchinsky]

Thanks guys, I can and will use the proper guage THNN. This sounds like the proper way to do it. I was thinking of Romex because it seems simpler to do i.e. one cable to pull instead of three. But the increased difficulty of pulling romex in conduit partly offsets the benifits. Thank you all very much.

[Alan Tolchinsky]

Alan, Codewise there is no problem running 12/3 inside emt. Derating is not an issue with 1 or 2 cables. As Dev stated using type THHN wire inside of the conduit is easier and more practicle. What area of Maryland are you located?

Charlie

I'm in Rockville now just North of D.C. but will be moving to Raleigh soon hence my next post. Thanks.

[john whittaker]

Hi Alan, Welcome to NC and Raleigh. Hope you have a good move.

[Alan Tolchinsky]

Hi Alan, Welcome to NC and Raleigh. Hope you have a good move.
I appreciate the welcome . I used to be stationed at Camp Lejeune many moons ago and look forward to the slower pace in N.C.

[Dev Emch]

Thanks guys, I can and will use the proper guage THNN. This sounds like the proper way to do it. I was thinking of Romex because it seems simpler to do i.e. one cable to pull instead of three. But the increased difficulty of pulling romex in conduit partly offsets the benifits. Thank you all very much.

Quick tip to make life easier. Follow the minimal fill factor for EMT but if you think its going to be a hard pull, bump up the EMT size a bit. Secondly, set up your THHN spools to feed concurently into the pull. Tie up and tape off the end of *ALL* wires your going to pull. Then pull this run through the EMT while your wife, son, etc. monitors the proper feeding of the EMT at the entry end. Make sure you not chafing or scraping the wire on any sharp edges as its going in. Use pulling soap if you need to to lubricate the pull. Personally, I hate ROMEX. Actually I hate it because others love it. The others are those with large wearable front incisor teeth and they like romex jackets and insulation as a method to keep these choppers worn down and in check! If you know what I mean! Also Romex uses lots of paper and some romex actually uses a degradable cloth exterior (my home has some of this junk in it!).

[Barry O'Mahony]

NM cannot be left exposed The NEC permits NM to be used in both exposed exposed as well as concealed work; 336-6 specifies requirements for exposed work. Although, I'm with Dev and don't use NM in outbuildings due to the "rodent factor". I cringe when I see it run exposed in barns housing horses; 'just waiting for disaster IMHO.

[lou sansone]

BTW if you do decide to pull THHN and don't want to buy 3 spools of wire, you can go to the HD or other supplier and they will pre bundle them for you right off the rack with what ever colors you want ( I am always in 3 phase mode so I fool around with most colors except green and white/grey ). makes the pull easy

lou

[Alan Tolchinsky]

Quick tip to make life easier. Follow the minimal fill factor for EMT but if you think its going to be a hard pull, bump up the EMT size a bit. Secondly, set up your THHN spools to feed concurently into the pull. Tie up and tape off the end of *ALL* wires your going to pull. Then pull this run through the EMT while your wife, son, etc. monitors the proper feeding of the EMT at the entry end. Make sure you not chafing or scraping the wire on any sharp edges as its going in. Use pulling soap if you need to to lubricate the pull. Personally, I hate ROMEX. Actually I hate it because others love it. The others are those with large wearable front incisor teeth and they like romex jackets and insulation as a method to keep these choppers worn down and in check! If you know what I mean! Also Romex uses lots of paper and some romex actually uses a degradable cloth exterior (my home has some of this junk in it!).

Dev, Thanks for the concise tutorial on this. I really appreciate it. Now I'm going to print this out in preparation for brain fade. :)

[Alan Tolchinsky]

These are some great tips I'm getting here! I think I can do it. Does anything change if this is going to be in a townhouse? I'm thinking I'd better get it all inspected for legal purposes. Make sense?

[Rob Will]

I like PVC conduit and fittings. More often than not, metal wiring devices become a conductor when problems occur. For example: damaging insulation when pulling wire through metal conduit fittings. Go ahead and get a few rolls of THHN. You will use it often.

A wire pulling tip: Use your shop vac to draw a tiny bit of rag on a nylon string through the conduit. Attach your bundle of wires and pull everything back through. If you go ahead and buy the rolls of wire, you can make a simple spool rack to pull from. A spool rack works best laying in a horizontal position.

A plastic conduit tip: Non metalic seal-tite conduit can be direct glued into PVC conduit and fittings. Just give the PVC glue a little extra time to cure. The long swaged end of a PVC conduit works good to receive a seal-tite like this. Looks really clean.

Rob

[Jim Becker]

The NEC permits NM to be used in both exposed exposed as well as concealed work; 336-6 specifies requirements for exposed work. Although, I'm with Dev and don't use NM in outbuildings due to the "rodent factor". I cringe when I see it run exposed in barns housing horses; 'just waiting for disaster IMHO.
Perhaps, and without reading that section, I have to assume I'm talking about the requirements I have locally. Outside of the cables running down the backer board to join the breaker box, anything below ceiling level has to be installed in the wall or in conduit for surface mount as I have done in my shop. (Obviously applies to basements and garages, etc.) My surface mount conduit runs only go from ceiling level to the outlet to meet that requirement.

Honestly, it makes for good common sense not to have a soft-jacketed cable accessible to hands and sharp boards...as well as the horse incisors you happen to elude to... ;)

[Jim Becker]

Does anything change if this is going to be in a townhouse? I'm thinking I'd better get it all inspected for legal purposes. Make sense?

Ah...then find out what the local requirements are before you do the work... ;)