Today, I spotted a rep for a cable company (As in saleman for wire manufacturer) who was showing off his wears. One iten in particular that he was trying so hard to pump up was an MC cable with #12 insulated circiut conductors (Copper), and a #12bare AL ground conductor. Like AC it would fold back to the connector, and become the ground path, with an "approved for ground" fitting. Anyway, I have always understood that the major difference between MC, and AC to be the equipment ground conductor. I questioned this salesman on this, and he inssted that it was listed as MC, not AC. And that this was "the way of the future", of course. So I looked more closely, and yep, it said MC on the tape.. So my question is, what are the differences between MC and AC cable?
I know only the obvious differences, MC has an insulated EGC whereas AC doesn't, and MC is made from AL whereas AC is steel.
There is nothing in article 330 that says it has to have an insulated EGC and the White Book says it could be insulated or bare. The only question is whether #12 aluminum meets the requirement of 250.122 <table> for a 20a circuit (the 12ga copper circuit conductors and I think not. Sure it wasn't a #10 al?
gfretwell, the size is one of the key things I noticed... #12 Al bare against the sheath, maybe they consider them as a combined conductive path? As I really wasn't paying too much attention past the sales pitch, I can't remember who made it, but it was listed.
This is from the NFPA commentary in the Handbook....
The armor of interlocking Type MC cable is not recognized by UL as the sole means of providing an equipment grounding circuit but may be used to supplement the internal grounding conductor.
If an individual equipment grounding conductor is installed with a multiconductor Type MC cable installation, the separate equipment grounding conductor must be an integral part of the multiconductor Type MC cable. The size of an equipment grounding conductor is determined according to 250.122.
The following explanation applies only to installations of single-conductor Type MC cable. If single Type MC conductors are installed as open runs or as messenger-supported wiring, the smooth or corrugated metallic sheath on each conductor must have sufficient cross-sectional area to comply with Table 250.122 or concentric conductors may be provided over the conductor under the metallic sheath. Either the metallic sheath or the combination of the concentric conductors in parallel with the metallic sheath may be used to provide the required equipment grounding path. For single Type MC conductors with an interlocking metal tape armor installed as open runs or as messenger-supported wiring, concentric conductors must be provided over the conductor under the metallic sheath. The total cross-sectional area of the concentric conductors must comply with Table 250.122.
If single Type MC conductors are installed in cable tray, the cable tray, an equipment grounding conductor(s) within the cable tray, and/or the equipment grounding provided with the single conductor may be used individually or in any parallel combination to provide the equipment grounding path required by 392.3(C) and 250.118.
So maybe they are considering the conductor and sheath as "the cross-sectional area to comply with Table 250.122"
I did debate with the guy about it's supposed ease of instalation, and box fill benifit. As I don't see it as any easier than making up the grounds, and if you're worried about box fill of grounds, you already have too many in the box IMO. Also mentioned to him that many people don't even like EMT as a ground path, this would be a hard sell for those types. As the whole path would be compromised by a loose lock-nut. Regular MC also has a benifit, of providing enough GEC to have a pig-tail for a device if you play your cards right. And on jobs where I has supervised the install, I know which MC in a box is the path to the panel as the feed to that box, as it is the one that grounds the box. With this stuff I wouldn't know....
I believe this is one of the newer MC cables designed for Article 517 applications. One of the manufactures has been advertising a HCF MC cable but I don’t remember which one. If so the bare conductor is only used to provide low resistance of the interlocking armor and is not designed to be connected to anything.
Curt
Curt, he did have that HCF cable, and this other MC, truthfully I could not tell the difference between them.... Other than another ground...
Besides the difference in how grounding is accomplished, AC has "an overall moisture-resistant and fire-retardant fibrous covering" (to wit, paper) over the conductors, whereas MC does not.
I believe that both types can use either steel or aluminum for the armor. Or more correctly, the material isn't specified, except that it be "metallic"; presumably stainless steel or brass would be legitimate as well.
I read about this new MC cable awhile ago and yes it is MC.
The manufacture had to get UL to change the listing requirements for MC in order to produce the product.
The original MC specifications required an overall wrap of plastic, in order to have that 12 AWG AL outside of the plastic wrap the rules had to change.
If I recall the 12 AWG AL is considered as a listed assembly with the sheath creating a reliable ground path.
You can terminate the 12 AWG AL but you do not have to.
Bob
In IAEI magazine's "UL Question Corner"(May-June 2006 issue), there's a 1/2 page Q&A describing the new MC Cable. (For some reason the page is marked January-February).
Southwire, the manufacturer of the new type cable,has a full page ad for their new cable in the same issue.
I'm sure it's purely coincidence
![[Linked Image]](https://www.electrical-contractor.net/ubb/rolleyes.gif)
MC has an insulated EGC whereas AC doesn't, and MC is made from AL whereas AC is steel.
Both AC and MC Cable are available with aluminum or steel armor, and both can have an insulated grounding conductor.
The new stuff, as well as a whole slew of other information is available at
http://www.southwire.com/Southwire/StaticFiles/PriceSheets/AS05.pdf The new type MC-AP cable is shown on page 6.
The latest IAEI mag has an ad for the stuff.
Unlike AC, you don't need to fold back the wire, just cut it off. Also unlike AC, this wire is full sized- not just a little ribbon.
The ad claims UL listing and classification as MC for this product. Unlike most MC, this stuff is limited to dry locations only.
Since I just saw the ad, it will probably not be available for six months.
I thought about posting this a few weeks ago, but never got to it.
One of the EC's showed me a piece of 'new MC', with the tag on it. Bare alum 'grd'. He wanted to use the 'bare grd' as the grd conductor for the circuit, & bond it to his boxes, etc.
After a quick look, I asked him how he was going to terminate the alum at the boxes, etc??
The look on his face was priceless!!!
Bare alum looked like a #10, but I can't swear to it. Have not seen this EC, nor the new MC since.
Considering the copper situation, it may be coming sooner then we think.
John
The southwire web site does say the bare ground is up one size. I am curious about the termination too. With oxidation in mind I can't imagine the incidental contact with the shield will work.
Btw, in cruising the web sites looking for this MC I saw a lot of whining about the price of aluminum too. It is still cheaper than copper. Nothing would surprise me.
The CPSC and that Inspect-Ny site still have a hard on against aluminum.
I've only seen a sample of this stuff. My boss brought sme back from a seminar a few months back. I'd have to assume it would most likely be used in hospitals or where an isolated ground is necessary.
You guys have me confused.
As far as I know we will not be terminating this AL bonding strip, just cutting it off like we do with AC cable.
I understand your practical answer Bob but MC armor is not suitable for grounding so we must be depending on the EGC wire. The bonding strip in AC is to shunt out impedance in long runs of armor. The EGC in MC must be that ground and it may not actually have that much contact with the armor on a short run.
I am still waiting to see the connector this stuff uses. Of course if you bring it into the box all we need is an Al rated lug. I see that as the best choice, perhaps a double so you can splice the "goes outta" EGC.
I'm sure, if this stuff is cheap enough, somebody will come up with the missing hardware within a price range that makes sense.
Greg the point of this new MC is that the armor will be a reliable ground path.
![[Linked Image from iaei.org]](http://www.iaei.org/subscriber/magazine/04_c/trainorfigure4.gif)
I found the article I read about this.
Here are couple of key parts.
The size of the bare aluminum grounding/bonding conductor is based on NEC Table 250.122. Cables with 12 AWG copper current-carrying conductors are constructed with a 10 AWG bare aluminum grounding/bonding conductor. Cables with larger current-carrying conductors have appropriately larger sized bare aluminum grounding/bonding conductors.
Most important was clarification that the new cable had been tested both with the bare aluminum grounding/bonding conductor simply cut off and also with it folded back over the armor and that these tests had been conducted with many different types of listed fittings.
The entire article which has a ton of info can be read here at the IAEI
http://www.iaei.org/subscriber/magazine/04_c/trainor.htm Bob
[This message has been edited by iwire (edited 05-18-2006).]
Greg, as Iwire points out, the sheath of this new MC will be recognized as an EGC per 250.118 and will allow MC to be used in 517 applications.
Other than that, I don't see where it will take the place of AC or HCFC.
With the larger AL bonding strap along the length of the MC smart cable, verses the smaller strap in AC, I can't see how it will be any cheaper.
Granted, I do like working with MC better than AC or HCFC though.
Roger
Maybe I'm missing something, but I don't see how you could use it in a patient care area. Isn't the EGC bare? That would violate 517.13(B).
Also, given the choice between a 10 AWG bare conductor to work with (MC) or an 18 AWG bare strip to work with (AC), I would prefer the strip. Why would a person buy this???
On second thought, I guess you could use it for wiring luminaires above the patient care area and use 517.13(B) exception 2, ...but why?
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.
AC does not depend on the incidental contact with a 10ga internal conductor for the fault path.
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.
The "new" MC that I had seen had 1 ungrounded, 1 grounded, 1 insulated EGC, 1 #10 AL, and the metal-clad casing was painted hospital grade green.
The Green HCFC is used alot arround here in patient care areas with approved grounding type connectors, using the bare ground for box and insulated for Hosp grade recept. We also will use it with some ig circuits .The metal clad for more exposed area`s and alum clad for not subject to damage.All are truck stock.
Roger, in todays labor market it is hard to find good help, never-mind someone who is awake in the morning enough to put a lock-nut on, and tighten it... It seems better care goes into make-up, and EGC wires are superior to this sheath connection IMO. Also, I can see some future goofs in the way of snipping the wire back and knicking the other conductors. Or the sharp edge of the sheath bond turning into the isulation of the others during install.
Bottom line, I would be a skeptic until forced to use it...
Talked to an Inspector here about it yesterday, she said we should check back with the city before doing a job in it. So that 15 inspectors to debate before I'll do anything with it.
[This message has been edited by e57 (edited 05-19-2006).]