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MC cable

Posted By: sparkync

MC cable - 06/07/14 02:38 AM

I'm looking at an old 2005 code book, and it gives the qualifications for MC cable to be used in wet locations. The location I'm figuring is just damp, not actually wet. It says the conductors are to be listed for wet locations, covering to be impervious to moisture etc.. Does the MC cable that is normally bought, say at Lowes, fit these criteria? Thanks
Posted By: electure

Re: MC cable - 06/07/14 04:15 AM


There's a type of MC cable that has a PVC jacket on top of the armor, Southwire calls it Parking Lot/Deck Cable.

Special connectors must be used with it, as well. The connectors have a gland nut, much like the gland nut on a cord grip.

From 2011 NEC, 330.10(A) :

(11) In wet locations where any of the following conditions are met:

a. The metallic covering is impervious to moisture.
b. A moisture-impervious jacket is provided under
the metal covering.
c. The insulated conductors under the metallic covering
are listed for use in wet locations, and a corrosion resistant jacket is provided over the metallic sheath.


Normal MC does not fit the bill frown



Posted By: gfretwell

Re: MC cable - 06/07/14 05:06 AM

Most aluminum jacket MC is listed "wet", simply because they use a wet location conductor inside the jacket.
(per (c) above).

Posted By: electure

Re: MC cable - 06/07/14 01:31 PM

Greg, are you sure?

(c) also states "and a corrosion resistant jacket is provided over the metallic sheath."


Both AFC and Southwire say their aluminum armored MC is listed for "Dry use only"


Posted By: gfretwell

Re: MC cable - 06/07/14 04:48 PM

This is the box I have in the garage.

[Linked Image from gfretwell.com]
Posted By: electure

Re: MC cable - 06/07/14 06:29 PM

From the 2005NEC:

(11) In wet locations where any of the following conditions are met:
a. The metallic covering is impervious to moisture.
b. A lead sheath or moisture-impervious jacket is provided under the metal covering.
c. The insulated conductors under the metallic covering are listed for use in wet locations.

The code Changed in 2008 it's present verbiage, and also first prohibited FMC in wet locations, too.

Could it be you bought cable pre-2008?






Posted By: Tesla

Re: MC cable - 06/07/14 11:01 PM

It would appear the committee is trying to stop the use of MC and Greenfield as HVAC condenser whips.

In commercial work they have long been considered unacceptable.

Yet you see them all over town, hereabouts, powering up HVAC condensers -- pad mounted -- residential.

With this rule change, Sealtite or PVC coated MC becomes required.

Since I can't point to any fire risk issues, it would appear to be a code change motivated by the NEMA players.

Posted By: gfretwell

Re: MC cable - 06/08/14 02:26 AM

I certainly see no issue with the cable above.
The inside of a raceway is still a wet location if it is outside and THWN is a wet rated conductor. What difference does it make if the rain is getting into the MC/FMC? Is it any wetter than a buried raceway is filled with water?

I have seen plenty of regular aluminum MC outside. You just need the cables arranged so they don't fill the boxes with water (typically bottom entry)
Posted By: renosteinke

Re: MC cable - 06/08/14 05:40 PM

There's never really been an issue with MC itself in a wet / outdoor location. You're doing just fine until you get to the end of the cable.

Why? Because every MC connector I've ever seen has been marked as for 'dry locations only.' There's the problem.

Were it not for the price of the (weather-tight) fittings, I suspect we'd see a lot of UF used as HVAC whips.

------------------------

As I learned the trade, the only material considered for such whips was metal-lined "Sealtite." I will admit that there is still a role that only such a method can meet.

Yet, I wonder if we're trying too hard to be 'perfect?' For the applications we're discussing, we're using "normal" 20- or 30-amp 120 power. Even the use of 240 in residential air conditioning is becoming rare. It seems a natural application for a less elaborate method - even (gasp!) a cord and plug.

Frankly, I'd have greater faith in a cord & plug than I currently have in the typical installation, where the flex is falling out of its' connectors and the connectors are hung on a disconnect that seems to be made of foil, and is usually improperly mounted.(How often do you see one of the mounting holes wide open to the weather?)
Posted By: gfretwell

Re: MC cable - 06/08/14 07:24 PM

I never understood why you were not allowed to glue LFNC into a male adapter (except that Carlon would lose a couple bucks)

They do let you glue up ENT.
Posted By: electure

Re: MC cable - 06/09/14 01:11 AM


A while back, I did some experimenting with the LFNC into PVC M/A thing.

After some failures I ended up sanding both the flex and the M/A with 220 grit sandpaper, priming each with PVC primer, applying Light Bodied PVC Cement to both, and assembling it.

I left it overnight to cure. When I came back to test it, the flex pulled right out of the PVC fitting.

The glue hadn't bonded to the flex.
I gave up at that point.

Posted By: gfretwell

Re: MC cable - 06/09/14 06:00 AM

I use Otey all purpose with primer and you can't pull one out, at least with the force it takes to pull out a regular LNFC fitting.

If this stuff was white it would be Spa Flex and they put pools together with it.
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