MC/AC Clamp in bracket boxes

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Rick Haupt

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Is there a requirement that bracket boxes that have the internal MC/AC clamp be used on 250volts or less only? Or is this a jurisdictional item?
I have always used standard boxes with ko's and external clamps on 277 swicthes.
 
To the best of my knowlege, code requires MC/AC flex to be terminated with the approved connector for the specific product.

Those internal straps in some boxes with the small KO are not used much in my jurisdiction, and I do not approve them if used for MC/AC. They are OK for NM cable or SO if the situation warrants....

Great care must be taken with MC and AC because of the sharps, and with MC, the jacket is not rated as a legal path to ground. It becomes inductive and creates a impedence to ground which can cause failure to trip the breaker in a dead short condition. Therefore a separate equipment ground is required and the cable has some limitations on use, such as patient care areas where redundancy of ground pathways are required..

Local codes may vary, but the code seems pretty clear to me on this matter.

Personally, I quit using those boxes years ago....:) They are called plaster boxes and originated to facilitate work on plaster/lattice construction in homes that is no longer used much since drywall was invented...IMO

You may be dealing with some old city codes or something....I dunno...
 
wirestripper said:
To the best of my knowlege, code requires MC/AC flex to be terminated with the approved connector for the specific product.

Those internal straps in some boxes with the small KO are not used much in my jurisdiction, and I do not approve them if used for MC/AC. They are OK for NM cable or SO if the situation warrants....

Local codes may vary, but the code seems pretty clear to me on this matter.
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Why would you not approve them if the clamps are listed for MC/AC ?
Appleton box clamps are.
http://www.appletonelec.com/pdf/AppletonClamps.pdf
 
If the appleton is used, with the proper clamp, I will approve it, but only after physically inspection every termination.

What usually happens is that they use the NM clamp and try to tell me that it is a approved box. It is not.

So I strongly suggest that they use the proper connector with the built in or add on bushing. The best ones are all one unit and make the connection almost flawless everytime. No bushings to install.

I do this for their benefit, as I know how shorts can arise and they are very difficult to locate once the building is trimmed out. I have seen electricial spend days looking for them...resulting in huge finacial losses and re-do's.

But yes, if a approved clamp is in that box, and after consulting the cable MFG's recommendations, I can not find any requirement saying not to use them, I will approve them after inspecting the workmanship and looking for cuts or punctures in the insulation.

I love MC, and have used it a great deal. But you must be aware of the risks with it.
 
It sounds like You don't like them. God you must spend hours on a job that has 200 boxes if your looking at everyone!!
All the boxes we use have approved clamps for both AC and MC. We have been using them for 30 years now.
I can't remember ever having any call backs for cut wires from the clamp.
I seen cut wire from use with a hacksaw ( showing my age) but with everyone today using rotosplit I see no problem at all.
With old work boxes thats all we use is the clamp
 
"but with everyone today using rotosplit I see no problem at all.
With old work boxes thats all we use is the clamp".....


It is largely a situational thing....

I don't believe there is any local who uses a "Roto", and they don't do much MC installation, so their apprentices, who usually do this task, are not really very good at it. The local supplier, of which there is but one, does not stock the boxes with the approved clamps and sells them whatever he has on hand. Needless to say, I am not a welcome person in his store because I have complained about this practice years ago,

So I deal with it the best way I can.

I just inspected a medical facility this past weekend, and found romex connectors (lock nut type) used throughout the building for standard MC. Each box had sharps hanging into the cavity and all were illegal.

After checking with the city, I discovered the building was just on the other side of the city lines and not in my jurisdiction. So I refered the matter to the state on Monday.

Generally speaking, I am teaching as well as inspecting, it is a role I must play and if apprentices do not get guidance, they make mistakes. If I don't catch the mistakes, I have a State Board to answer to, and they don't listen to excuses. Both the contractor and myself are subject to losing our masters ticket, and that is the story.

The use of the appleton is not the problem. It is the improper installations where the wire is not even in the guides, or was cut too short and pulled far too tight to make it up.

I have no problems with MC that is installed properly, and in fact I fought some local codes that once prohibited it.

I do prefer AC. but MC has a place and I encourage it's use. It cuts time of the job and is easy to pull. But the terminations must be done right, as is the case with any wire method.
 
No, they are not. Only the approved device is, which can be with a built in ferrul or a bushing, which can be separate or built in.

The bushing is only a part of some of the approved devices. I find the separate bushing devices to be a pain in the butt...but the bushing is not necessary in most of them and if it is, it is stated, or it is built into the fitting.

I tried to make that clear because it is a common complaint against some inspectors.

I believe you are referencing a brand (don't recall but "red dot" comes to mind)that encloses a little baggie of red bushings, and you often lose them. That particular bushing is not a required part of the assemby.
 
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So! iif I use a listed internal clamp (for MC) or external connector (listed for MC ) and do not use red heads even if provided by the Cable MFG, you would pass the installation as code compliant?



Ruling out extranious other violations???? of course


Charlie
 
Yes....certainly.

As I tried to explain, it is largely a workmanship issue.

The old work box, or plaster box (as I call it) is not sold here with the correct internal clamps for MC/AC and many electricians use the standard box with the NM clamps. It is that box and the apparent confusion about the internals that has caused a problem with MC installations in Arkansas.

We only recently adopted the apprentice program, and only this past year has the system been ranped up to a competant level. All the older electrician were grandfathered into the system and never tested. It was a mess for a while, but we have finally got a good handle on it and the tradesmen are responding to it favorably. In fact, we just now had our first mandatory continuing education seminar of the 2005 book.

So compared to the guys in Jersey, we are just now becomming comperable in our regulation and training.

But I still have a lot of work to do to get everyone up to speed. Mostly the old farts like myself who have been doing it this or that way for decades.

But it's coming along just fine now.

The red bushing issue came up some years ago, and the State Inspectors made the call, not I. However, from my own personal observation of that particular fitting, I found the bushing to be nice and the fitting better if installed with one, but I don't gig the job if they are missing or misshapen. The edges of the metal opening restrict the wires movement, even without the bushing and the edge is not sharp.
 
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Wirestripper, are you saying that red heads are not neccesary for AC and it is just a workmanship issue? What manufacturer list a connector that makes the use of an Anti Short Bushing not necessary for AC? I know AFC did at one time but I think that has been removed.

Roger
 
We don't gig the job for a missing bushing (anti-short).

If I recall, back in the 99 NEC, there was a requirement for a anti-short bushing to be installed. At that time I was still working my business, and I stopped using the red head, or dot or whatever and went to a metallic ferulled bushing to avoid the problem entirely.

When I first started inspecting, I enforced the bushing rule.

Since that time, the State inspectors office has suggested that I do not enforce it.

Upon study of the 2005 book, section 333 which addressed the bushing installation in MC fittings has been removed and and now it only says that the fitting must be approved for use with MC with the bushing laguage dropped from the page.

So,,,,,,,,,,,,,,,,,,,based on all that, we no longer enforce it.

But I remain very concerned about shorts and the workmanship in MC installations. I recommend metal ferruled fittings or the kind with built in bushings and I will not allow un-approved clamps.

But the little plastic thingy language is no longer in the code.
 
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Wirestripper, there are different requirements for AC than the are for MC.

AC

320.40 Boxes and Fittings
At all points where the armor of AC cable terminates, a fitting shall be provided to protect wires from abrasion, unless the design of the outlet boxes or fittings is such as to afford equivalent protection, and, in addition, an insulating bushing or its equivalent protection shall be provided between the conductors and the armor. The connector or clamp by which the Type AC cable is fastened to boxes or cabinets shall be of such design that the insulating bushing or its equivalent will be visible for inspection. Where change is made from Type AC cable to other cable or raceway wiring methods, a box, fitting, or conduit body shall be installed at junction points as required in 300.15.
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MC

330.40 Boxes and Fitting
Fittings used for connecting Type MC cable to boxes, cabinets, or other equipment shall be listed and identified for such use.
Click to expand...

As you can see the Anti Short Bushings or equivilant are required in addition to the connector for AC but not for MC.

Edited to fix quote

Roger
 
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I have been addressing MC, the entire thread.

Earlier, I said that I much preferred AC, but that is not what I have been addressing.

Secondly, now that you mention AC, where is the bushing in that Appleton Box that everyone seems to like so much.:)
 
wirestripper said:
I have been addressing MC, the entire thread.

Earlier, I said that I much preferred AC, but that is not what I have been addressing.

Secondly, now that you mention AC, where is the bushing in that Appleton Box that everyone seems to like so much.:)
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You got to put it in!!!

For Type AC cable, insert an anti-short bushing and bend back the exposed length of bonding strip. (The bonding strip bends back before or after the bushing inserts.) Follow the same procedure for MC cable, with the exception that there is no bonding strip.

Here is a web site from a wire company that shows you. Read bottom of page 3 and look at the photos on page 4
http://www.afcweb.com/pdfs/afcpocketguide.pdf
 
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"As you can see the Anti Short Bushings or equivilant are required in addition to the connector for AC but not for MC."


Yes.........

All true....

Around here I don't see too much AC. It is used extensively in industrial settings or Hospitals.

The fittings are usually the unitized type with bushing installed so there is no red thingy to lose or misplace.

It is MC that I have problems with in my inspections, and I could easilly fill ECM's little "can you believe this" section with photos of some wild MC installations. I mentioned one of them that I saw this past weekend, earlier in this thread.

But again, regarding bushings on it, I can no longer enforce, but only suggest.

As for AC.....The problem has never come up. Not once.

There is a big difference between a qualfied industrial electrician, which I am one, and the residential masters who may over-extend their reach. Not to mention the Uncle who used to work for the power company.

You fellows back East have never had to deal with the sort of things that I do, and you likely resent inspectors a bit.:) But I accept that.

My job is not to screw up the profit margins on a bid, but it is to represent the governments interests in getting the work done in as safe a way as possible and according to the code where it is applicable.

It is all about safety and protectiong the electricians who work in my jurisdiction from mistakes that could cost them their livelyhoods and their employee's paychecks.

That is what I do.

If I saw a fitting with a sharp edge and no bushing, I would say something regardless of the code requirement. But I can't make him put it in anymore on MC.

In fact, after the 2005 book came out, they took a lot of the inspectors teeth away and now I am a suggester. But I never misused those teeth in any case. I have really been a suggester all along, and the way I get compliance to to gain the trust of the contractors who work here.

You can't gain trust by demanding that work be done a certain way, unless you can back it up with logic and code. I don;t think there are any electricians in town who don't want to see me. The vendors are another story, because I am always on their case about stocking the right stuff.:)
 
OK.....Let me say again, that these boxes and bushings are not used properly here. I stared out by saying that I don't generally approve their use. They are not sold here with bushings or the proper clamps!

The vendors do not carry anything but the romex version, and they never sell the bushings.

The problem with these things is that they do not come together with a bushing installed. Them some idiot buys them and uses them improperly so I tag the heck out of them.

This is all about MC. Not AC.

It is MC that is being misused in my jurisdiction and others in Arkansas.

It is one of my pet peeves,,,,,,and it is due to ignorance mostly, from the vendors to the masters.

I'm not one of those pricks who stand around acting like God or the Governor of electricity. If a electrician meets my concerns in any number of sensible ways, I will approve the installation.

Where I have the most problems, is where the two fields of residential and commercial/industrial intersect. And that is where MC cable is.

Not AC.....
 
"Read bottom of page 3 and look at the photos on page 4
http://www.afcweb.com/pdfs/afcpocketguide.pdf"


Yes, I have that book in my code book. I use it all the time for a teaching aid.
 
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