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Old 11-10-2013, 08:43 PM   #1
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Running NMD-90 wires through a conduit


Hi! When doing renovations a couple of years ago on my bungalow, I ran a 2.5" conduit from the unfinished basement to the attic. I did this with the idea that I could run some NM (Romex type) wire from my electric box to ceiling locations (in one blog, an electrician referred to this kind of setup as a "sleeve"). I did this without checking code requirements and now that I have wires to run, I want to know if I can do this. The conduit has one 90 bend at the base, goes up about 10 feet inside a wall, comes out in the attic, has another 90 bend and extends another 6 feet on top of the ceiling joists. The plan was just to be able to fish the wire up there, so the conduit is not connected to anything (open both ends). I am contemplating running a 3-10 NM (Romex) cable for a 5000W garage ceiling heater about 80 ft from the panel (using a 30A breaker) and a few 2-14 NM cables for lighting. The 3-10 was cheaper than 2-10 but I won't be using the common. Am I allowed to run NM wire inside this conduit and if so, how many 2-14 cables can safely be run in addition to the 3-10?

Also, one problem with this pipe going from my basement to my cold attic is condensation dripping down at the basement end in winter. Could I use spray foam at the top side of the pipe (not a thick layer) once my wires are through, to prevent warm air from going up the pipe? or are there other solutions?

Thanks.

Last edited by Horseonaboat; 11-10-2013 at 08:46 PM.
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Old 11-10-2013, 11:42 PM   #2
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ok this a little complex...since this piece of conduit(sch 40 or 80?) is over 24" you can only fill it to 40% 310.15ba see exceptions as well...and you can only sleeve 10' so you will need to cut it back...there are or can be heat build up issues..
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Old 11-11-2013, 02:54 AM   #3
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Quote:
Originally Posted by Bobka View Post
...and you can only sleeve 10' so you will need to cut it back...
This is a common local rule but not in the National Electrical Code. Check with your inspector.

For this size wire, derating for bundling usually does not become an issue until you go over nine current carrying conductors. Add 2 for the 10/3 and 2 for each xx/2 with ground. That's one 10/3 and three 14/2s in your case.

To increase the number of circuits in a sleave, use Multi Wire Branch Circuits or up the wire size.

Expanding foam is useable but a b#tch to remove. Electrician's putty is better and available at most hardware stores.
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Old 11-11-2013, 03:17 AM   #4
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A 5000W heater at 240V pulls 27.8A. Multiply by 1.25 for a continuous load, that's 34.8A. You can't use #10 wire. You need #8 and a double pole 40A breaker.

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Old 11-11-2013, 09:20 AM   #5
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The Op specified NMD-90. That is a Canadian cable designation so it would be safe to say he is in Canada and NEC does not apply.
Derating also applies so you will probably need #12 for 15 amp circuits and #8 for the 30 amp circuits.
Bushings will need to be installed on the ends of the conduit to protect the cable.
Also PVC conduit can not be buried in insulation so if the wall is insulated, you can't even use the conduit.
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Old 11-11-2013, 02:41 PM   #6
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I should have mentioned I'm in Canada... sorry eh!

Thank you for the quick replies.

From the replies and from looking at the NEC (I'm assuming Canadian derating rules are similar??? Is the ampacity of Canadian NMD-90 14 gauge = 20; 12 gauge = 25; and 10 gauge = 35?), I can only have 3 conductors in the conduit without having to derate (I don't want to use Multi-Wire Branch Circuits). Although I'm not going to use the 3rd wire of my 10-3 cable, I should calculate 3 conductors in case someone in the future sees it as an opportunity to connect something else (you never know what someone might install in a garage). Since I already have the 10-3 cable (not returnable), I would only be able to conduit that 1 cable to feed my 5000W garage heater (5000W x 125% = 6250W / 240V = 26A) with a 30A breaker (what a waste of 2.5" conduit . Did I understand right? I might as well fish my 3-10 cable through the wall (any problems with going through Roxul Sound&Safe sound proofing wool?) and use the conduit for lighting circuits. I'm calculating that (without the 10-3) I can run up to 3x 14-2 cables (6 conductors): ampacity 20 x 80% = 16... still good with 15A breakers. Or up to 3x 12-2 + 1x 12-3 cables (9 conductors): ampicity 25 x 70% = 17.5... still good with 15A breakers. If I run my 12-gauge wire through the conduit to a light fixture, can I then use 14-gauge wire to the next light fixture?

*Thank you Joed for that mention about PVC conduit and insulation.

*Glennsparky... did I miss something when you say that my 5000W / 240V heater is pulling 27.8A. I calculated 20.8A and then times 1.25 I get 26A... good for a 30A breaker (of course no derating).

*Bobka... I'm curious to know where the 40% fill value comes from... 310.15 (B) says that a 40% adjustment would be for 31 through 40 wires. Also where does the 10-foot sleeve limit come from? I figure a sleeve cannot be more restrictive than if the whole circuit is in a conduit.

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Old 11-11-2013, 04:54 PM   #7
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Quote:
Originally Posted by Horseonaboat View Post
*Glennsparky... did I miss something when you say that my 5000W / 240V heater is pulling 27.8A. I calculated 20.8A and then times 1.25 I get 26A... good for a 30A breaker (of course no derating).
You are right. My calculator went bad. $2 and only 10 years old and I had to throw it in the garbage. What a waste.
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Old 11-12-2013, 09:05 AM   #8
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Quote:
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You are right. My calculator went bad. $2 and only 10 years old and I had to throw it in the garbage. What a waste.
It's the Canadian exchange rate for current.
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Old 11-14-2013, 01:28 AM   #9
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PVC conduit in insulation


Quote:
Also PVC conduit can not be buried in insulation so if the wall is insulated, you can't even use the conduit.
Hi Joed... I had several surprised responses when I mentioned this. I'm told this does not apply to US. Where can I find info on this rule for Canada? Thanks
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Old 11-14-2013, 08:40 AM   #10
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12-1102
Rigid PVC shall not be used where enclosed in thermal insulation.
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Old 11-14-2013, 09:57 AM   #11
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Joed, can other types of conduit be used in insulation? Why no PVC?
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Old 11-14-2013, 12:38 PM   #12
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Don't know the reason behind it. That is what the code says. I do not believe metal conduit has this restriction.

It only appears to be for "Rigid PVC Conduit". The sections titled "Rigid types EB1 and DB2/ES2 PVC Conduit" and " Rigid RTRC Conduit" do not have the restriction. I could not even guess what the difference between those types are.
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Old 11-14-2013, 12:40 PM   #13
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Strange, the NEC does not have the same restrictions on PVC.
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Old 11-14-2013, 06:12 PM   #14
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Quote:
Strange, the NEC does not have the same restrictions on PVC.
It seems a lot of jurisdictions do not allow PVC pipe inside at all due to fire codes.
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Old 11-14-2013, 06:53 PM   #15
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Most of the insulation on the wiring and cable jackets are all PVC also. The fumes from all the furnishings would be way more than from the conduit.
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