AC cable versus MC cable

[charlie b]

Wire types are not my strong suit, and I an new to this project. So any help will be appreciated.

Our design documents called for MC. The contractor wants to use AC (I think they may have already bought it, and are hoping we let it go). The installation is indoors, neither damp nor wet, and none of the other restrictions of 320.12 apply. I don't have a good reason to say no. Does anyone have such a reason? Should I be suggesting that the contractor offer a rebate to the owner for (what I am guessing will be) the less expensive wire?

 

[iwire]

I would say no.

AC typically has no copper grounding conductor, it relies on the armor as the grounding conductor. You can get hospital grade AC with a copper grounding conductor but I would be shocked if that is what the contractor plans on using.

On the other hand typical MC has an insulated copper grounding conductor.

 

[ActionDave]

AC is just like MC only different.

I say go ahead and let the contractor use the AC.

 

[Joe Villani]

Does your design spec (16131) call for a equipment ground conductor to be run in all raceways that are installed?

If no then I would accept the AC cable.

Joe

 

[iwire]

If the bid called for MC and now the contractor want to use AC ... I would look for a credit if I allowed it. No EGC is a labor saver.

 

[Jon456]

Our design documents called for MC. The contractor wants to use AC. The installation is indoors, neither damp nor wet, and none of the other restrictions of 320.12 apply. I don't have a good reason to say no. Does anyone have such a reason?

To better answer your question, it would help to know what type of loads are on these branch circuits. For example, if lighting, I'd be less opposed to AC. But if for computers or electronic equipment, or if powering machinery for example, then I would insist on MC.

 

[Jon456]

You can get hospital grade AC with a copper grounding conductor but I would be shocked if that is what the contractor plans on using.

Wouldn't you more likely be shocked with regular AC cable? :lol:

 

[iwire]

To better answer your question, it would help to know what type of loads are on these branch circuits. For example, if lighting, I'd be less opposed to AC. But if for computers or electronic equipment, or if powering machinery for example, then I would insist on MC.

That is pretty much my thinking as well.

I once substituted short lengths of MC for AC when doing a lot of track light feeds. Getting rid of the grounding conductor in the small end feed speeds things up.

 

[Ponchik]

I did a quick check on the pricing and the AC cable is about 15 cents more per foot than the MC cable.

Unless it is a spec job and you requested the bid to be with MC, I would let it go and allow them to use the AC cable.

 

[gadfly56]

I did a quick check on the pricing and the AC cable is about 15 cents more per foot than the MC cable.

Unless it is a spec job and you requested the bid to be with MC, I would let it go and allow them to use the AC cable.

Well if the AC is actually more expensive, then in my view (as others have stated) it comes down to how critical the grounding needs, if any, happen to be.

 

[iwire]

Well if the AC is actually more expensive, then in my view (as others have stated) it comes down to how critical the grounding needs, if any, happen to be.

AC is more expensive to purchase, it is less expensive to install.

Basically it does away with all grounding connections especially if you use self grounding devices reducing labor costs.

 

[MasterTheNEC]

Wire types are not my strong suit, and I an new to this project. So any help will be appreciated.

Our design documents called for MC. The contractor wants to use AC (I think they may have already bought it, and are hoping we let it go). The installation is indoors, neither damp nor wet, and none of the other restrictions of 320.12 apply. I don't have a good reason to say no. Does anyone have such a reason? Should I be suggesting that the contractor offer a rebate to the owner for (what I am guessing will be) the less expensive wire?

@ Charlie b

Actually I will tell you from a manufacturers perspective (and I will leave it at that)...it actually costs less ( roughly $6.00 less per 250') to produce AC than MC Cable. You can trust me or not but I can promise you that is the case. The choice of which to use is purely a design concern and of course an NEC concern where applicable.

Now what the a distributor charges per MC or AC is out of the manufacturers control but it probably has more to do with supply and demand than actual production costs. It seems that everyone loves MC Cable but AC Cable is a fine product in itself.

So if the plans spec for MC Cable and someone wants to use AC Cable I would not loose any sleep over it. As long as they document it, stamp it and install it correctly.

 

[GoldDigger]

So if the plans spec for MC Cable and someone wants to use AC Cable I would not loose any sleep over it. As long as they document it, stamp it and install it correctly.

And as long as anybody who maintains or extends the system recognizes that the cable/raceway is being used as the EGC and connects their EGCs properly to it....

 

[gadfly56]

AC is more expensive to purchase, it is less expensive to install.

Basically it does away with all grounding connections especially if you use self grounding devices reducing labor costs.

Your points on labor are well taken.

On price, see post #9, as at least one person has contradictory data, at least for his locale.

 

[ron]

Charlie,

MC over AC any day of the week. Unless your spec for MC allows for stuff like the self grounding MC cable, such as Southwire's http://www.southwire.com/oem/2008NECChangePermitsSelfGroundingMCCableInManufacturingWiringSystem.htm
you have every reason to stand up for the requirement of regular MC. My spec calls for a copper EGC in every raceway and cable, so unless it was hospital AC (which has a ground wire, so I would consider it), as pointed out, stay with MC IMHO

 

[petersonra]

I don't see any significant difference based on what you have said.

If they are coming back after the bid was awarded and asking to have the spec changed, there should be some kind of discount applied. My guess is that it won't amount to all that much.

It always makes me wonder when contractors come back after a bid has been awarded and want to change something.

 

[petersonra]

Incidentally, I see AC as being potentially better than MC, so maybe my perspective is a little different than others.

In my mind AC has a conductor woven through the armor that just about guarantees the armor is properly grounded.

Regular MC has no such guarantee since it does not have the conductor woven through the armor so there is at least some potential for the armor on the MC to be energized and not trip the BC OCPD, while that seems less likely with AC, assuming both are installed correctly.

 

[cdslotz]

Ahhhh....those pesky specs.

 

[iwire]

In my mind AC has a conductor woven through the armor that just about guarantees the armor is properly grounded.

It is not woven in it just runs along the inside but either way it is a grounding path.

However many AC fittings are crap so even though listed for grounding the connection is a poor one. (Particularly any of the push in type)

Regular MC has no such guarantee since it does not have the conductor woven through the armor so there is at least some potential for the armor on the MC to be energized and not trip the BC OCPD, while that seems less likely with AC, assuming both are installed correctly.

MC has a copper grounding wire that results in both ends of the armor being grounded even with a break in the armor or a bad fitting.

 

[MasterTheNEC]

And as long as anybody who maintains or extends the system recognizes that the cable/raceway is being used as the EGC and connects their EGCs properly to it....

Well....we honestly can't plan for the future without knowing what is being installed today. As for inspectors, they are inspectors not expectors so what someone MAY do down the road is always a possible concern. We just have to hope knowledge and training rules the day!