Power and phone lines for the shop - meeting the NEC

Bob Davis · 2003-10-28T14:55:58+00:00

Years ago, I actually owned a copy of the National Electric Code and kept upwith it, as an electrical engineer in an industrial situation. I no longerwork as an electrical engineer and I've never had to know much aboutresidential applications, so I have some dumb questions.I'm running a new power feed and two phone lines to my emerging shop. I'vesettled on running individual #6 power lines with a #12 ground. I'll runall of this through a 1" PVC conduit to get from the existing breaker paneloutside to a point where I can bring the wires into the attic and over tothe garage shop. I also will have a 4 conductor telephone-type wire. Itscleaner to run the phone line in the same conduit as the power, but I'mconcerned about two things - electrical noise pickup and compliance withNational electric code. As to the noise, I can always run the cable and ifits noisy, just abandon it in place.If you have any knowledge about NEC with regard to running phone lines andpower in the same conduit, please let me know.Yes, this is related to woodworking. The power will run a complete new setof tools - table saw, dust collector, jointer, drill press, planer, bandsaw, and coffee pot. The phone line will be used to call my woodworkingfriends when I get stuck with a problem in the shop.Thanks in advance for your comments.Bob

Oct 28, 2003 67 Replies

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Doug Miller 22 years ago

Pulling *wires* through conduit is easy. You were pulling a *cable*. You had a lot of factors working against you:

a) First and foremost, Romex cable is composed of *solid* wires. There just isn't a lot of flexibility there. Especially in 10-gauge. It's much easier to pull *stranded* wire.

b) Bundling wires together in a cable reduces flexibility still further. It's much easier to pull four individual wires than one 4-wire cable -- even if you wrap them together at the point where you attach the fish tape, and pull all four at once, it's still easier than pulling a cable.

c) Cable sheathing isn't especially slippery either. THHN/THWN wire has a hard, slick outer layer that makes it positively glide through a conduit.

d) Romex tends to twist up as it's paid out, which compounds the friction and flexure issues.

e) Were you using a wire-pulling lube on the cable?

f) How many pull boxes did you have in the middle of this 75-foot run? It's probably overkill, but I usually install a pull box every two or three sections of conduit. It makes life much easier.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

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Bob Davis 22 years ago

I'm cheating. I'm doing individual wires and assembling the conduit over the wire and mounting it - slide on a section, bolt it down, etc. I'd hate to charge by the hour to do it this way, but its easier on a guy with back problems. :-)

Bob

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Gfretwell 22 years ago

It's not really legal, but again, I doubt the wiring police will be knocking on your door. In fact that is how FPL runs long service laterals here. I see it all the time. The code assumption is any raceway system is built such that the wires can be pulled in and out at any time. That makes a lot of sense in a commercial setting but the code is a "one size fits all" affair. When I asked my boss how I should use 90-4 (the inspector discretion clause) he said "just make it safe". Your method is safe IMHO.

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Morgans 22 years ago

You should be using individual wire, not romex. As a matter of fact, there is something in the code that reduces the amount of wire that can be used if it is romex, as I recall, but I don't remember exactly what it was. Temperature rise, or something.

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Morgans 22 years ago

Power lines should be buried at least 3 feet.

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Bob Davis 22 years ago

Actually, then end result will physically be the same as if I had run the conduit and pulled the wire through it. I just happen to have the luxury of being able to put up one 10 foot section of conduit at a time because the run is not that long (70 feet). I'll have pull boxes and two 90 degree bends in the conduit. I just don't want to pull it because of my back.

I appreciate your practical comments.

Bob

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Gfretwell 22 years ago

Cables pulled into conduit has to be computed as a conductor using the widest dimension as the diameter. If you twist the cable a few times the widest dimension IS the diameter. 12-2 Romex won't "fit" in 1/2" conduit because of this. If you have ever tried to pull it through a few bends you would agree. Most inspectors will ignore this for short sections of conduit used for supplimentry protection, like down the wall of your garage or shop. 3 wire with ground is usually smaller than 2 wire in the computation since it is closer to round with a smaller diameter.

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