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#181515 10/14/08 07:22 AM
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Been awhile since I have used NMD90 but I have a question in regards to it's proper used in conduits. I know that NMWU is for direct burial. As well according to Table 19 NMD90 is approved in damp locations, so does this mean NMD90 can be run under ground in a PVC conduit where moisture can exist?


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NMD90 is not approved for wet locations. Underground is wet not damp so if you really want to put the cable in a raceway then the cable and the raceway must be approved for wet locations.
A cable like NMWU that is approved for direct burial can be installed in Non Electrical raceways like poly pipe. City lighting was often done by direct bury of a poly water hose using a ditch witch and then using jacketed xlink to feed the light standards. More municipalities now use ENT and regular wet location wire. The big advantage of the poly pipe was the direct burial which removed the dig, install, sand the trench, mark the trench, inspect and bury. The alternate was drive a tractor down the street and tamp the sod down behind the tractor. I think ENT can be installed like this where acceptable.

mikesh #181521 10/14/08 12:37 PM
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Thanks for your reply. It has been so long since I worked with NMD90 and I couldn't remember if NMD90 could be pulled into a pvc raceway underground or if it still had to be NMWU, which in that case I would not have a full run of PVC. I would of thought it was a damp location since there would only be condensation in the pipe.


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The D in NMD is for DRY.
The W is for WET.

jdevlin #181543 10/15/08 09:49 AM
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Originally Posted by jdevlin
The D in NMD is for DRY.
The W is for WET.

I agree, I was a little unsure when T19 approves NMD90 for damp locations. I guess you would need the thermoplastic insulation to get the damp location rating yes? cool


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The damp location is like a mushroom barn or even a regular barn. Subject to condensation.
It is a common misconception to think of a glued PVC pipe underground as Dry. The ground is cold and if the air is humid the water in the air can condense in the U/G pipe. Lots of dry pipes are wet pipes after a few years of collecting water from the air. Some ground slab pipes do stay dry but both ends are usually in the same building and the ground is at least partly heated by the building so the pipe stays above the dew point and the water stays in vapour. I have seen a few data runs where the wire was for a dry location and the cable in an underground location gets wet causing data troubles. Hard to gat a customer to install gel filled U/G cable at 10-20 times the cost of a regular cat5 cable or telco cable.

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I've asked the AHJs about NMWU in conduit (besides a short sleeve for mechanical protection) and been shot down. The argument is the cable can't properly dissipate the heat from carrying the current its rated for.

As a result, I've stuck with RW90 in pipe, direct buried and/or protected NMWU, or direct buried ACWU.

u2slow #181859 11/04/08 01:37 PM
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I don't know if it is true that the cable would be compromised in a raceway. Did you ask the boys in the Victoria office? The cable can be wrapped in thermal insulation which would definitely affect its ability to dissipate heat.

u2slow #182366 11/24/08 08:52 PM
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Originally Posted by u2slow
I've asked the AHJs about NMWU in conduit (besides a short sleeve for mechanical protection) and been shot down. The argument is the cable can't properly dissipate the heat from carrying the current its rated for.

As a result, I've stuck with RW90 in pipe, direct buried and/or protected NMWU, or direct buried ACWU.


FYI
I was reading through my Ontario Bulletins from the ESA and found something that relates to using NMWU in underground PVC conduit.
Specifically, bulletin 68-7-4 under Wiring Methods talks about what conductors you can use in a PVC underground conduit.
3.1.2. "Rule 22-200 rerquires individual conductors and non-metallic sheathed cables in Category 1 areas to be suitable for use in wet locations. Non-metallic sheathed cables shall be of the NMW or NMWU type."

So I don't know why it would be allowed in Ontario but not in BC. When you think about it, what you were told doesn't make sense.

Cheers... Bruce

brsele #182463 11/27/08 07:55 PM
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22-200 does not say NMWU can be installed in a raceway it says it may be installed in a category 1 (wet) location.
Table 19 does not list Loomex of any designation for installation in a raceway so in a raceway it may not be installed.
The heat thing is at best a reach for an answer to prevent the installation of loomex.
Can anyone explain why they want to install it in a raceway? I cannot understand installing a pipe then sticking a cable in it. Expense without benefit?

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