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  1. #1
    Join Date
    Apr 2007
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    Default When should you use an anti-short bushing?

    I just had an electrical inspection today on a commercial building. I roped the entire project with MC cable and I used Arlington Industrie's 38AST connectors throughout. I was told that a separate anti-short bushings was not needed when using this type of connector because it was built into the connector. The inspector disagrees. He is under the impression that they are required in conjunction with the 38ast connector and states that he has spoken to arlington Industries and they confirm this. I asked the inspector if he had a "letter of interpolation" from Arlington Industries or any other recognized authority, he stated no but was willing to intertain any recogized authorities recommendations on the subject.

    I spoke to the Arlington Industries rep. today and he said that this question has come up before and that the anti-short bushing was not required but could not get me anything from the manufacture for about a week or more.

    Can anyone help shed some light on this one?

    TXS Phil

  2. #2
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    Default Re: When should you use an anti-short bushing?

    330.40 of the National Electrical Code works for me
    Seeking to be the best and the safest in the electrical trade.

  3. #3
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    Default Re: When should you use an anti-short bushing?

    I agree that Arlington does not specifically state that you don't need to use a red head when using these fittings but I must admit I have had some trouble using them with these fittings as well as the "push-push" snap in fittings. Somehow they don't seem to seat properly when you use a red head and I have used them without. I'm not really sure if I did the right thing. If you look at the demo in this link http://www.aifittings.com/whnew87.htm you'll see that they are merely inserting the MC cable into the fitting without using a red head. However, they refer to this as an insulated throat and do not indicate that this throat slides up into the armor of the MC cable preventing the metal from cutting into the conductors. I think it merely serves the same purpose as a plastic conduit bushing. By the same token, if you were to use a duplex MC connector it only has one insulated throat and you would have to use a red head to protect the wires in each cable. With that in mind I would say that you should use the red heads in either case unless Arlington can provide some documentation indicating the you don't need the red heads. Just my 2 cents worth.

    Mike, section 330.40 only states that the fittings used for MC cable shall be approved for such use. It doesn't make any reference to using red heads to protect the insulated conductors.

  4. #4
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    Default Re: When should you use an anti-short bushing?

    Quote Originally Posted by goldstar View Post
    Mike, section 330.40 only states that the fittings used for MC cable shall be approved for such use. It doesn't make any reference to using red heads to protect the insulated conductors.
    As Joe has pointed out in his post the insulating bushing is not required with MC.
    Here are the code sections that apply to both AC and MC Cable.
    Notice that one requires the red bushing and the other don’t.

    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.

    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.

    As the two sections show the AC Cable requires the red bushing where the fitting is installed but this is not a requirement for the MC Cable fitting
    Seeking to be the best and the safest in the electrical trade.

  5. #5
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    Default Re: When should you use an anti-short bushing?

    Good info Joe and Mike. Thanks for setting us straight on this.

    Aside from what the NEC clearly states, I'm still having a hard time with the logic behind why AC cable requires a red head while MC does not. I can see where a single MC connector with an approved insulated throat would or could do the job in replacing a red-head but I can't see it in a duplex connector. There's only one insulated throat. In addition, AC cable has a shunt wire traveling throughout its metal sheathing as part of the design of its grounding system whereas MC does not. Do we not consider the sheathing of MC cable to be grounded when properly terminated ? Isn't it possible for the sharp-cut end of an MC cable to cut into an insulated phase conductor (as in AC cable) thereby energizing the sheath or shorting out ?

    I know I think about wierd stuff but if anyone knows the answer would you please post it here ?

    Thanks,

    Phil

  6. #6
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    Default Re: When should you use an anti-short bushing?

    Quote Originally Posted by goldstar View Post
    Isn't it possible for the sharp-cut end of an MC cable to cut into an insulated phase conductor (as in AC cable) thereby energizing the sheath or shorting out ?

    I know I think about wierd stuff but if anyone knows the answer would you please post it here ?

    Thanks,

    Phil
    Phil,

    An inspector told me once, though I can't quote a written source, that it has to do with the wrap underneath the metal sheathing. AC cable has that thin brown paper wrap around the individual conductors, easily damaged, whereas MC has that tough clear plastic around the set of conductors, much less susceptible to being damaged by the sharp edge of the sheath.




    LEE

  7. #7
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    Apr 2007
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    Default Re: When should you use an anti-short bushing?

    This is GREAT! I have found a lot on this subject from so many knowledgable people but for some reason I could not find these two sections of code on line. It is the last piece I needed before I state my case to the Inspector. I don't think he's going to like it.

    I started to work the MC Cable out of the termination fitting to install the redheads as directed but only ended up damaging the conductors to the point that I did not feel comfortable leaving it in and I found myself replacing each run, not good.

    I need to speak to Arlington Industries, I think that the part number [38AST] stands for a 3/8 fitting and AST is an acronym for Anti-Short Termination. Does anyone know?
    Last edited by Pzlaket; 04-07-2007 at 11:02 AM.

  8. #8
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    Default Re: When should you use an anti-short bushing?

    Quote Originally Posted by edlee120 View Post
    Phil,
    AC cable has that thin brown paper wrap around the individual conductors, easily damaged, whereas MC has that tough clear plastic around the set of conductors, much less susceptible to being damaged by the sharp edge of the sheath.




    LEE
    This is correct

    Quote Originally Posted by Pzlaket View Post
    I need to speak to Arlington Industries, I think that the part number [38AST] stands for a 3/8 fitting and AST is an acronym for Anti-Short Termination. Does anyone know?
    This is correct
    Seeking to be the best and the safest in the electrical trade.

  9. #9
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    New Jersey
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    Default Re: When should you use an anti-short bushing?

    Phil,

    An inspector told me once, though I can't quote a written source, that it has to do with the wrap underneath the metal sheathing. AC cable has that thin brown paper wrap around the individual conductors, easily damaged, whereas MC has that tough clear plastic around the set of conductors, much less susceptible to being damaged by the sharp edge of the sheath.

    LEE
    Lee & Mike,

    I'm having a tough time buying into your claims that the mylar wrap in MC cable is less susceptible to cutting than the brown paper in AC cable is. While the cuts seem to be cleaner with the aluminum jacket in MC it is still possible for the ends to be compressed inside a box clamp or MC connector. It is my belief that while the insulated throat may help to insure that the conductors are kept straight when entering a JB, it is also possible that the clamp-down feature of the connector could force the edge of the armor to cut through the mylar and into the phase conductors. BTW, we still haven't addressed a duplex connector with only 1 insulated throat.

    Just my opinion. I'm not an employee of any fitting manufacturer, a test technician for UL or a member of any CMP. So, what do I know !!!

  10. #10
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    Apr 2007
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    Default Re: When should you use an anti-short bushing?

    Quote Originally Posted by jwelectric View Post
    This is correct



    This is correct
    TXS Mike! How did you come to know this? Do you have a source document?

    Phil

  11. #11
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    Apr 2007
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    11

    Default Re: When should you use an anti-short bushing?

    TXS Mike! How did you come to know this? Do you have a source document?

    Phil

  12. #12
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    Default Re: When should you use an anti-short bushing?

    Quote Originally Posted by Pzlaket View Post
    TXS Mike! How did you come to know this? Do you have a source document?

    Phil
    See the link that Joe and Goldstar posted.
    Seeking to be the best and the safest in the electrical trade.

  13. #13
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    Oct 2006
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    Massachusetts
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    Default Re: When should you use an anti-short bushing?

    [QUOTE=goldstar;283996]Lee & Mike,

    I'm having a tough time buying into your claims that the mylar wrap in MC cable is less susceptible to cutting than the brown paper in AC cable is. While the cuts seem to be cleaner with the aluminum jacket in MC it is still possible for the ends to be compressed inside a box clamp or MC connector. It is my belief that while the insulated throat may help to insure that the conductors are kept straight when entering a JB, it is also possible that the clamp-down feature of the connector could force the edge of the armor to cut through the mylar and into the phase conductors. BTW, we still haven't addressed a duplex connector with only 1 insulated throat.

    QUOTE]


    Phil -

    I've seen only one instance I can remember offhand where MC shorted at the connector, whereas there have been many instances (in my 25-plus years in the trade) that I've seen Bx short out at a termination. So that tells me that the MC is designed better: there is more room inside the sheathing than with old stuff and then there is the mylar wrap. BTW have you ever tried cutting or tearing that stuff without a knife? When I remove the paper on Bx I unpeel it then yank it back against the edge of the sheathing and it tears off easily. Can't do that with the mylar, it won't tear.

    The connectors that are being discussed are not the only listed MC connectors and there are some that are uninsulated: http://www.bptfittings.com/specifica...LOG_ID=560-DC2 . So the insulated throat is not really the pertinent issue with the listing for MC.

    It seems to me that your concerns about the wire being damaged by box clamps or a connector clamp-down feature MIGHT fall into the realm of good workmanship vs. poor. The clamps should be tightened appropriately and not over-tightened. This is something we face all the time: how tightly to install Rx staples, for example. How much torque to put on a lug 'cuz too much and it might crack the next time it has to carry a significant load. There is at least one Rx connector that will crush a piece of 14/2 or 12/2 romex if overtightened and cause a short (I've had it happen to me!). When I can find the right link I'll put it up here.

    I'm not arguing that we shouldn't use redheads for MC (I always use them) but I do like knowing what's required and what isn't, and why.

    Yers..........LEE
    Last edited by edlee120; 04-08-2007 at 08:50 PM.

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