ECN Forum Forums General Topics of the Trade General Discussion Area New MC cable?

Ryan, the article seems to be mainly addressing the sheath, not all of the conductor configurations that will be available.

Now, whether it is true or not, (I have not tried very hard to research this stuff) I was told by one of our suppliers a year or so back that there is (will be) an MC smart equivilant to HCFC which would have an insulated EGC.

Roger

Lab tests are great but I would like to see a test of some of this MC, shoved in a snap in fitting with the ground cut off and installed in a beach house for 10 years. (or pretty much anywhere with 90% humidity most of the time). If we can't keep a wire under a binding screw from oxidizing to the point it fails, how can this "intimate contact" last very long?
I really worry when the piece of MC is pretty short, like a whip to a big motor, and that "intimate contact" is only hitting 20 wraps or so. I guess it really doesn't take that much to operate the O/C device but that does tend to fly in the face of 250.122

Greg, why would it be any different than AC being used in a beach house or high humidity area for 10 years?

Roger

AC does not depend on the incidental contact with a 10ga internal conductor for the fault path. I am not really sure why there is a difference between AC armor and MC armor but I didn't write the code.
I always considered the main improvement we got with MC was the hard wire ground. Now I guess that is gone. Let's see how time deals with it. I am old enough to remember Alcoa on TV telling us how great aluminum romex was.

Right. It depend on contact with an 18 AWG conductor...even smaller than the one in MC.

Greg I agree with Roger and Ryan.

It is the AL bonding strip in intimate contact with the AC armor that makes the Armor suitable as an EGC.

I agree with you that a lot of the snap in AC or soon to be MC connectors are pretty scary when used as the ground fault path.

I won't order them, I stick with clamping type connectors that I can really tighten.


Bob


[This message has been edited by iwire (edited 05-18-2006).]

The practice of winding the bonding strip back up the outside of the armor of AC cable does nothing to enhance the low impedance ground path. It is a custom that began so the inspector could see that it was indeed AC cable. It could be cut off flush with the armor without any ill effect. (This is a big advertising point with the new MC cable, that it can be cut off flush)

Yep Bob this is the stuff I was talking about... Sorry gents about the confusion over the bond wire size, although it did look very suspiciously like #12 to me, and I swear the guy I was talking to told me #12 too....

IMO I really don't think this stuff will be any easier to work with. And I have enough problems getting people to tighten locknuts on EMT as ground, never mind an MC connector, and the connection to the MC - connector. So that 2 connections to fail....

E57, there are no more connections on this MC (or any MC) than there are on EMT or AC connections. The connector must be tight on the conduit or cable and the locknut (if the particular connector utilizes a locknut) must be tight, that is it, no more.

Roger

If the artwork in the ad is to be believed, the main point of thes "new stuff" is to completely eliminate the green wires from the junction box. A device would still need a pigtail to the box- but there would no longer be a clutter of green wires.