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Ground wire in MC cable

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  • mbrooke
    replied
    Originally posted by romex jockey View Post
    you forgot HI's MBrooke...~RJ~
    Don't get me started But yes, valid point.

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  • romex jockey
    replied
    you forgot HI's MBrooke...~RJ~

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  • mbrooke
    replied
    Originally posted by romex jockey View Post
    JMHO, but the jacket is 'wound' and (i'm told) 5-6 X's the length of interior conductors

    they found this out with the old BX

    if the shell was energized , it wouldn't trip

    but not always because it was made off K&T, because of VD

    we'd see this line of dots, in the old horsehair plaster...and we knew....

    ~RJ~
    That sad part is DIY sites tell HO to take a tester to the box. If it lights, you may now proceed to install 3 prong outlets... just bond to the back of the box.






    Home Center books are the same, creating the idea armor is always an low impedance path:







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  • romex jockey
    replied
    JMHO, but the jacket is 'wound' and (i'm told) 5-6 X's the length of interior conductors

    they found this out with the old BX

    if the shell was energized , it wouldn't trip

    but not always because it was made off K&T, because of VD

    we'd see this line of dots, in the old horsehair plaster...and we knew....

    ~RJ~

    Leave a comment:


  • hbiss
    replied
    So I'm still looking for how and why MC originated. All you see is that it's an iteration of BX and AC.

    -Hal

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  • mbrooke
    replied
    Originally posted by hbiss View Post
    Looking for the history of when and why MC came about, I found this. From the Mike Holt archives, a post by Thomas Horne dated Feb. 25, 2002:



    So here we have yet another opinion that MC came about because a separate insulated EGC offers a more reliable ground conductor.

    -Hal
    Could be... but I think that involves a lot of "magical" thinking. Not saying thats how the code thinks/thought, but I personally on my own disagree. However, I thank you none the less for showing me this.

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  • hbiss
    replied
    Looking for the history of when and why MC came about, I found this. From the Mike Holt archives, a post by Thomas Horne dated Feb. 25, 2002:

    Originally posted by Thomas Horne
    The restrictions on wiring methods are based on the fire history of that type of occupancy. Since the jacket of type AC cable is the Equipment Grounding Conductor (EGC) if the jacket is damaged the EGC will be broken. In type MC cable any damage that will break the separately insulated EGC is likely to break the other circuit conductors and fault out the circuit. So in places were physical damage to the cable is more likely, such as a commercial garage or movie studio AC is forbidden. In places were large numbers of people are at risk such as movie theaters it is also forbidden.
    So here we have yet another opinion that MC came about because a separate insulated EGC offers a more reliable ground conductor.

    -Hal

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  • mbrooke
    replied
    Originally posted by infinity View Post
    How's this for a guess, the cable was originally designed for pools where an insulated EGC was required and MC was easier to run than a metallic raceway. Of course this has changed.
    Never thought about it that way.

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  • infinity
    replied
    How's this for a guess, the cable was originally designed for pools where an insulated EGC was required and MC was easier to run than a metallic raceway. Of course this has changed.

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  • mbrooke
    replied
    And two AWG sizes smaller? I don't know of any connector that takes less than 12 AWG aluminum.

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  • winnie
    replied
    One thing that makes MC-AP closer to normal MC than to AC is that that the full size ground conductor _may_ be used as a wire EGC in the same fashion as the green insulated EGC in normal MC.

    MC-AP is _marketed_ and generally intended to be used where you cut the EGC wire short and use the connection to the sheath via to cable clamp as the EGC. Essentially exactly the way AC gets used. However you are _permitted_ to bring the wire into the enclosure and splice just like any other wire EGC...except that your splice needs to be suitable for aluminium conductors.....


    -Jon

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  • hbiss
    replied
    Right. An insulated or bare EGC in itself doesn't make a difference as far as being able to carry a fault current and trip the breaker, sizes being equal.

    The difference above with HCF vs MC is that HCF provides a redundant EGC using the armor plus a separate EGC run with the other conductors. MC is prohibited from using its armor as an EGC and has a separate EGC run with its other conductors.

    Now they have MC-AP that has a full size bonding conductor under the armor allowing the armor to be used as an EGC. Like AC, there is no separate green grounding conductor. Only difference between it and AC is that there is no paper wrapping under the armor. Might as well call it MC-AC

    -Hal
    Last edited by hbiss; 10-08-19, 02:43 AM.

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  • mbrooke
    replied
    Originally posted by romex jockey View Post
    JMHO, it all comes down to a fault path>

    ~RJ~
    But a bare EGC wouldn't make a difference, right?

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  • romex jockey
    replied
    JMHO, it all comes down to a fault path>

    ~RJ~

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  • hbiss
    replied
    Or maybe it was done that way since they decided to add an EGC to NM way back in, what, the 30's? Why change it now?

    -Hal

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