Is it okay to protect NM Cable in an unfinished basement with ENT?

Question

Adding a 20 amp subcircuit (120V) to furnace room to turn it into a workshop. Initially it will have one duplex and 2 fourplex receptacles, the fourplex receptacles will be on cement walls, the duplex will be on a stud.

I know that for the duplex I just need to staple the cable back far enough so that if someone ever puts drywall up there will be no danger of hitting the wire with a drywall screw.

Section 334.15.c of the NEC 2011(which the state of MI uses) says

...Nonmetallic-sheathed cable installed on the wall of an unfinished basement shall be permitted to be installed in a listed conduit or tubing or shall be protected in accordance with 300.4.

I'm assuming they mean UL Listed conduit or tubing, which the smurf tube I'm looking at is. Am I correct in this assumption? Also, is this common practice, using ENT on exposed walls to a metal box? I know that the metal box (and metal tubing if I used it) has to be grounded, just making sure I'm not being too unorthodox with solution, or going against code.

Answer 1

You'll have to check with the Authority Having Jurisdiction, but I'd say "smurf tube" on a wall in a shop is a no no.

National Electrical code allows ENT for exposed work, but not where subject to physical damage. Which means if you're trying to protect your cable from physical damage, you can't use ENT (unless you protect the ENT from physical damage as well).

National Electrical Code 2014

Chapter 3 Wiring Methods and Materials

Article 362 Electrical Nonmetallic Tubing: Type ENT

II. Installation

362.10 Uses Permitted.

1) In any building not exceeding three floors above grade as follows:

a. For exposed work, where not prohibited by 362.12
b. Concealed within walls, floors, and ceilings

362.12 Uses Not Permitted. ENT shall not be used in the following:

(9) Where subject to physical damage.

If you don't want to use metal conduit, schedule 80 PVC conduit is identified for areas of physical damage.

Article 352 Rigid Polyvinyl Chloride Conduit: Type PVC

II. Installation

352.10 Uses Permitted.

(F) Exposed. PVC conduit shall be permitted for exposed work. PVC conduit used exposed in areas of physical damage shall be identified for the use.

Informational Note: PVC Conduit, Type Schedule 80, is identified for areas of physical damage.

Answer 2

I wouldn't rule out the use of Sch40 PVC here. In fact I would consider a length of sch40 PVC glued to the hub of a PVC box all well fastened to the wall a far superior choice, and it's virtually allowed per 334.15(B) "...or other approved means..."

EMT and metal boxes mounted to damp below grade masonary walls have way too many issues for me: possible sharp edges, proper grounding, corrosion.

Could you imagine an authority wondering if sch40 PVC used in this manner is strong enough in a residential basement workshop? I certainly couldn't.

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By not listing it 334.15(B) doesn’t explicitly approve sch40 PVC, but it doesn’t explicitly prohibit it either. If the code listed it here as approved, it would be used everywhere and obviously NEC doesn’t want that. But, at the same time, the code doesn’t say, “Sch40 PVC cannot be used “, that would be explicit. What it does say is, “or other approved means”, which means that it’s up to the inspector to decide.

And Speedy Petey, I realize that the thought of leaving something up to an inspector’s discretion can be a frightening thought, and, with that said, I think you’re 100% right if you prefer to be safe and to advise others to be safe than sorry. But if the code says it’s the inspector’s call than I have to standby what I originally said which is, “I wouldn’t rule out the use of sch40 PVC.”

I’m going to include the word for word, complete commentary for this code section from a NEC 2008 Handbook. This is probably what stuck in a couple of my brain cells and even though it supports my case it still doesn’t stop my head from spinning:

Section334.15(C) was revised for the 2008 Code to include crawl spaces. Crawl spaces pose dangers similar to those of unfinished basements and in some case are more dangerous due to limited height. The means of providing physical protection required by 334.15(B) includes specific protection techniques. Notice that Type PVC, Schedule 40 is omitted from this list unless it is judged as an “approved” means by the authority having jurisdiction. Also, where NMC is installed close to the surface in masonry, concrete, or adobe-type construction, physical protection must be afforded to the cable by using steel plate-type protectors as described in 300.4(F)

For exposed work in unfinished basements and crawl spaces, as described in 334.15(C), physical protection for nonmetallic-sheathed cables run on unfinished walls can take the form of any listed conduit or tubing (including polyvinyl chloride conduit, Type PVC, Schedule 40).

As illustrated in Exhibit 334.1, nonmetallic-sheathed cables installed in an unfinished basement or crawl space can be through joists and attached to the side of joists or beams and running boards. Section 300.4(D) requires cables that run parallel to framing members be installed at least 1-1/4 in. from the nearest edge of studs, joists, or rafters.

Answer 3

I agree that emt is the way to go if corrosion is a big concern you can use straps that stand the conduit off of the wall with a plastic washer between the wall and strap or a non metalic strap that does the same. Personally I would use metal as opposed to pvc because if a fire did occur pvc produces poisonous smoke. I think this may be one of the reasons it is not allowed in buildings over 3 floors. You could also use plastic washers between the concrete wall and the steel boxes.