I’m installing a motion-detector light and will need to conect it via conduit on the house exterior. I’ve had much experience with romex, little with conduit. My most recent experience – fished romex through 3/4 conduit, found it hard going, ended up fitting conduit over the cable, which seemed wrong. So, I am going to need some advice:
1. Total run will be about 15 ft, but I need to make 3 90 degree turns.
2. Should the turns be with those special pull boxes or with the long-sweep pre-bent pieces?
3. Metal or PVC? Or that new moisture-tight flexible conduit?
4. Cable or individual wires? If the conduit is PVC, do I need a ground wire? If, not, what happens to the ground wire in the romex when I make the romex-to-conduit, inside-to-outside transition?
Replies
I'm no expert but until someone else comes along.
Do not use romex, just individual wires. No ground wire if using metal conduit.
3-90's no problem. I believe code says 360 degrees max. Pre bent or bend yourself.
Use a pull lube when pulling your wires. Pull them all at once.
pull the ground wire anyways..
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No ground wire is OK if it's for lights but if there are any microprocessors in the device, dirty power is their biggest killer. Sure, the conduit can handle a lot of current but over time, the joints can and do add resistance.
"I cut this piece four times and it's still too short."
use thhn wire, no ground needed. run conduit first, push fish tape through, ore use shop vac to suck a string down the emt. attach wires, use lube, pull, easy.
"use thhn wire, no ground needed."ONLY IF IT IS METALIC CONDUIT. Even then, if EMT is used many people feel that it is good practice to pull a ground wire and the connection on EMT might work loose."ore use shop vac to suck a string down the emt."Not by itself.You need a "mouse" on the end of the string. A puffed up baggy is often used. Some thing to "seal" the conduit..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
> Should the turns be with those special pull boxes or with the
> long-sweep pre-bent pieces?
I use the long-sweep sections. You might want a pull box at the point where the conduit goes through the wall, or you might install a junction box rated for outside use at that point.
> Metal or PVC? Or that new moisture-tight flexible conduit?
I prefer metal.
> Cable or individual wires?
Use individual wires.
> If the conduit is PVC, do I need a ground wire? If, not, what happens
> to the ground wire in the romex when I make the romex-to-conduit,
> inside-to-outside transition?
If you use PVC, you'll need a ground wire. I usually run one even in metal conduit, but it may be overkill. You will make the transition from Romex to individual conductors in a junction box. This box will either be outside, in which case the Romex comes through the wall directly into the box, or it will be inside and the conduit will go through the wall. In either case, you can attach the Romex ground wire to the metal junction box and let the conduit serve as ground. As I said, I prefer to just run the third wire.
George Patterson
if you know how to bend EMT without kinking it ... use individual stranded wire instead of solid, it will pull easier for you through those three 90s.
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but it takes practice to learn how to bend pipe correctly, so you may decide on PVC..which may be the better choice in your situation....since you have mentioned moisture
if you do decide on EMT, (this would not be my choice )
don't forget to ream the cut ends before you couple them together and use raintight fittings.
Good Luck
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., wer ist jetzt der Idiot ?
Edited 4/30/2007 6:54 pm by maddog3
I would just qualify PGProject's response regarding ground:
If you use metal conduit, you don't need a ground, like he said, BUT only if the conduit is the ground, and you use metal boxes.
Here in Chicagoland, everything is in metal conduit/EMT, and the piping acts as the ground. If you have something different, make sure you have something as ground. It wouldn't be a big deal to run a third wire. And I like to add a ground wire on exterior fixtures (from the fixture to the box), because screws can corrode and you can lose the ground.
Bending EMT is no big deal. Buy a bender, buy some extra pipe (it's cheap), plenty of fittings, and have a go at it. Assemble your practice pieces, call it art, and sell it.
Cut it with a hacksaw or Sawzall with a fine blade (rather than with a tubing cutter). It leaves a much smaller burr to take off. And be sure to deburr, or you'll nick your insulation and make pulling more difficult than it needs to be.
(3) 90° bends, 3 THHN wires in 1/2" EMT shouldn't be that difficult. It would be easier to run a fish tape through and have one person pulling and one feeding.
Pete Duffy, Handyman
In your case, I would recomend PVC since it is easier to work with and intrinsically waterproof. For sharp, out side bends, use the special fittings known as condulets. You can bend PVC by heating it to about 212º. Do not use 1/2" PVC under any circumstances since it is so hard to pull.
The special waterproof flexible conduit you mentioned could be LiquidTite. That would solve the bend problems but it is rather sloppy in looks and the fittings are more expensive.
As for Romex in conduit, the Code is rather unclear, but then it is unclear in a lot of situations. Use individual wires including a green wire.
Don't forget the clamps. More is better. You need one within 3' of each box and then once every 10'.
For a 15' run, you should be able to push the wires thru.
~Peter
I agree, pull a ground.
The MGM Grand fire in 1980 was caused by heat in a bad connection in emt used as the ground. There was short in a box that fed a refrigerated display cabinet, that went to ground through the emt. Because of the bad connection it didn't pull enough to trip the breaker, but did generate enough heat to start a really big fire.
OK, so I'll use metal (this got most of the votes) but pull a ground to be extra safe. And individual wires. Should the ground be a bare wire? I will probably use the pre-bent corners or I may decide to rent a conduit bender. I did that, years ago, but my local rental place went out of business.
I haven't seen the water tight conduit fittings at HD that a poster mentioned. If I can't find them, I guess that would be an argument for PVC.
Thanks, guys, for all the help.
I just did this Sunday and used PVC. I like working with it better and it doesn't rust.Now I don't know where you are making the turns. But for going around a corner you need to use a coundit body or the conduit would stick way out. And say runnign vertically and then horizontally up on the wall personally I think that the conduit body looks better, but other might think that the sweep look better.Bare ground wire is more common in larger sizes (for ground electrodes). Typically in #14, 20 I see insulated..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill, what do you mean by this: "But for going around a corner you need to use a counduit body or the conduit would stick way out" ?
What's a "conduit body"? I definitely need to go around an outside corner. Do you mean that the radius of the pre-bent sweep is so big that it wil stick out even though the conduit is flat to the wall? I can't visualize this. Better go and look at some pieces!
Agree with Bill's comments on the Romex. It IS allowed in conduit... (assuming conduit is sized properly). That's a point often argued over, but Bill's right.
By conduit bodies, Bill is referring to LBs, LLs, LRs, and a host of other conduit fittings that can act as a pull point and allow you to sharply make turns (versus the typical "sweep" of a 90deg ell). Do a Google on "LB" & "Conduit" and you'll see what we're talking about. Big boxes typically carry LBs...
The conduit body is fitting that has 2 female openings in it. On one the end and the other in the back or right orleft side. Then it has a coverr over it.You don't fish through those. You remove the cover and it becomes a pullt point.Actually the make two other styles. One stright through where you just want to do a pull in the middle of a long run and a T.You need those to make sharp 90 turns. They are needed where you come out of wall and for an outside corner. You can use a radius for an inside corner depending on how it looks to you.http://www.cantexinc.com/p_access1.htm
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I know what you mean now -- I was referring to these as pull-boxes. Thanks again.
only use an insulated ground wire if you are going to use EMT.. as bare copper will eventually eat a hole on the pipe wherever it makes contact with it
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., wer ist jetzt der Idiot ?
You could probably use bare wire for the ground wire, but I use a conductor with green insulation.George Patterson
If you use thinwall conduit, I recommend using compression fittings for weather tightness - HD and Lowe's have 'em. Using pre-bent sweeps is easier than bending conduit yourself. I wouldn't bother pulling a ground wire if you use metal boxes. I have done rehab work in a lot of old houses with conduit and metal boxes and have had no problem with conduit grounds.Be sure to ream the cut ends before putting them together - makes the pull go easier and, with burs gone, you won't risk tearing up insulation. Klein offers a hand tool to ream both inside and outside of 1/2", 3/4", or 1" EMT in one quick operation - available at HD, Lowe's or any electrical supply house - looks sort of like a nut driver.
BruceT
In my opinion (not a pro, but a fair amount of experience), I'd pull the regular romex wire since individual wires will probably be more expensive in shorter lengths.
you definately have to use wire lube and pull each section through 3/4" PVC conduit separately; then glue it up after the wire is pulled.
A buddy who is a licensed electrician, said it was a code violation to put romex in conduit, and couple of electrical engineers I used to work with all told me that romex does not belong in conduit.
I haven't checked the code, but all three were people I have a lot of respect for, so I wouldn't be tempted.
"A buddy who is a licensed electrician, said it was a code violation to put romex in conduit, and couple of electrical engineers I used to work with all told me that romex does not belong in conduit. "Not true.In fact the code calls out the use of conduit (and other options) to guard exposed NM. One common place is in unfinished basements where NM is run down the wall to a receptacle.Now I admit that is a limited application and does not include any turns.But cable can be used in conduit. The problem is that you need to size to be a wire eqivalent to the larges width of the cable. And it is hard to pull..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
refer your 3 friends to NEC chapter 9, Table 1, Note 9, which explains the conduit fill calculation for a multi-conductor cable (Romex) in conduit.
You can't glue after the wires are in. The glue has the potential to melt the wire insulation if it drips inside.