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Old 05-24-2010, 07:10 PM   #1
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Bringing small wires out of a metal box


I'm putting in a raceway light/receptacle system in my garage, and it occurred to me that it would look much better, and save me some hassle, to route the control wires for the garage door opener through the EMT raceway as well. They are 22 gauge clx2, and I know they would need to be replaced with 22 gauge THHN, to match the insulation on the other wires in the conduit.

My question though is how to get them from the last box in the raceway system, a metal 4x4, out and into the garage door controller. The controller won't attach to a box, and is meant to sit flush to the garage wall. But I can't just route the wires through an open 1/2 inch knockout. Is there a way to get the two 22 gauge wires out of the metal 4x4 and still be NEC compliant?

Or if anyone sees another reason I should drop this idea, please chime in.

Thanks.
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Old 05-24-2010, 09:58 PM   #2
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You could just use a chase nipple on the box and run them open after that. Or you could run a short piece of pipe from the last box to a location near the sensor and put a bushing on the end of the pipe, running it open after that.
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Old 05-24-2010, 10:20 PM   #3
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But is it allowed to have an opening like that into a 4x4 box, even if several inches away from the box? I'm probably remembering this wrong, but I thought I saw in the NEC that there were to be no openings into the conduit system, to keep bugs, etc. I assume, from entering.

I guess I could just seal the end of the conduit nipple with silicone around the two wires.
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Old 05-24-2010, 11:12 PM   #4
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The important thing is that there must not be sharp edges that may cut the wires, as would be the case if you passed the wires through a knock out hole with no bushing or cable clamp or nipple.
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Old 05-28-2010, 02:58 PM   #5
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Wait wait wait... what you are proposing to do is run low voltage wire with regular wire in conduit - this is a no-no. The reason is if somehow the conductors came in contact, you would have low voltage devices suddenly receiving 120vAC - something they weren't meant to do.

You can run low voltage in conduit, you just have to make sure it is a separate conduit.
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Old 05-28-2010, 03:01 PM   #6
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Quote:
Originally Posted by xxPaulCPxx View Post
Wait wait wait... what you are proposing to do is run low voltage wire with regular wire in conduit - this is a no-no. The reason is if somehow the conductors came in contact, you would have low voltage devices suddenly receiving 120vAC - something they weren't meant to do.

You can run low voltage in conduit, you just have to make sure it is a separate conduit.
not true paul.

if the insulation is rated for the highest voltage (to ground) in the box or conduit, he is just fine. He already took the insulation into consideration as he posted in the first post.
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Old 05-28-2010, 04:49 PM   #7
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Woops! I missread that original post - thanks for clarifying!
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Old 05-28-2010, 06:09 PM   #8
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Quote:
Originally Posted by nap View Post
not true paul.

if the insulation is rated for the highest voltage (to ground) in the box or conduit, he is just fine. He already took the insulation into consideration as he posted in the first post.
If the Romex insulation is rated for at least 120vac, the low voltage wire insulation could be rated for at least 24vac, right?
Each wire protects the other wires, and the conduit, only from its own voltage?
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Old 05-28-2010, 06:56 PM   #9
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Quote:
Originally Posted by Yoyizit View Post
If the Romex insulation is rated for at least 120vac, the low voltage wire insulation could be rated for at least 24vac, right?
Each wire protects the other wires, and the conduit, only from its own voltage?
Wrong again. And what do you mean IF it were rated for 120 V?

The low voltage wire carrying 24 V would still need the same insulation rating as the NM.

Try reading the post over 3 hours before yours instead of this BS.
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Old 05-28-2010, 07:05 PM   #10
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I do low voltage HVAC control work and we typically use a knockout bushing to keep the insulation from wearing on the metal.
All the control wiring we use is rated for 600V, but we never mix it with high voltage, anytime we're in a starter we switch over to thnn.

Here's a link to what I'm taking about:
http://minerallac.thomasnet.com/view...ngs?&forward=1

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Old 05-28-2010, 07:52 PM   #11
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Quote:
Originally Posted by Yoyizit View Post
If the Romex insulation is rated for at least 120vac, the low voltage wire insulation could be rated for at least 24vac, right?
Each wire protects the other wires, and the conduit, only from its own voltage?
standard voltage ratings on typical wire are 300 and 600 volts. Most common wire today such thhn thwn are 600 volt rated wire.

now, the highest voltage (to ground) you are going to have in a residential situation is 120 volts. That means any wire you use must be rated at least 120 volts, even the wire that is only carrying 24 volts.

Reason why is if one of the 120 volt wires was nicked or the joint came apart or whatever that allowed a bare conductor in the box/conduit, if the low voltage wire were rated only 24 volts, that 120 volts could breach the lesser value insulation on the 24 volt rated wire and go wherever it goes.

If all the insulation is rated for at least the 120 volts, it could not breach that insulation and all is well.
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Old 05-28-2010, 08:02 PM   #12
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You could put something called a "strain relief cord grip" bushing I believe it's called, and run something like a round appliance cord through the hole. It will be a tight fit and it won't pull on the wires if you yank on it.

A good electrical house should have something like this, I haven't seen it at the big boxes.

Here is an example:
http://www.elecdirect.com/catalog/9a...e681be10c.aspx

Last edited by xxPaulCPxx; 05-28-2010 at 08:05 PM.
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Old 05-29-2010, 10:41 AM   #13
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Quote:
Originally Posted by Jim Port View Post
Wrong again. And what do you mean IF it were rated for 120 V?

The low voltage wire carrying 24 V would still need the same insulation rating as the NM.

Try reading the post over 3 hours before yours instead of this BS.
http://www.google.com/search?client=...UTF-8&oe=UTF-8
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Old 05-29-2010, 12:41 PM   #14
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Interesting discussion. But in the end, I changed my mind about running the garage door controller wires through the conduit. Though it probably would work out fine, I decided not to chance the possibility of the 20 amp wires inducing any significant amount of current in the garage door controller wires, not for any reason to do with NEC or insulation, but because it seemed like there was a chance that induced current could somehow damage the control circuits of the door opener. Instead I'll just run them separately around to the far side of the garage and back. A lot more wire, but peace of mind.

Thanks.
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Old 05-30-2010, 01:32 AM   #15
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