MC cable and Plastic Boxes

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goldstar

goldstar

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New Jersey
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Electrical Contractor
I hope this isn't one of those Code changes that escaped me again but I've been told by a CEU instructor that it is Code compliant to terminate MC cable in plastic JB's. IMHO, if the MC originates out of a metal JB or a load center it is grounded at that point. However, if you then leave that first plastic JB with MC and then go to another plastic JB that metal jacket is no longer grounded. Would someone please give me some insight on this ?

The reason I'm asking this is an EC friend of mine questioned me because he is wiring a residential garage and is concerned that rodents will chew through NM cable.

Thanks in advance.:thumbsup:
 
There is an issue of whether a plastic box is listed for a metallic connector, but I am only going to address bonding.


If the mc is bonded on one end from say a loadcenter and then goes to a plastic box I agree it is bonded, if one would wish additional protection, a bonding bushing or what not could be used also, I would probably do so.

For a cable between two boxes the cable would need to be bonded also, whether both ends is required here, I think not, but again, I would do so.
 
Take a look at 314.3

314.3 Nonmetallic Boxes. Nonmetallic boxes shall be permitted
only with open wiring on insulators, concealed knob-and tube
wiring, cabled wiring methods with entirely nonmetallic
sheaths, flexible cords, and nonmetallic raceways.

Exception No. 1: Where internal bonding means are provided between
all entries, nonmetallic boxes shall be permitted to be used with metal
raceways or metal-armored cables.
Click to expand...

Chris
 
jumper said:
I forget they clarified that part, in what-the1999, when I started out it was not so understood and a bit muddled. Was told more then once I could not do it.
Click to expand...

I actually don't remember which edition of the NEC this was clarified.

Chris
 
If the MC cable originates from a metal enclosure and lands in a nonmetalic box, why bother bonding that end too? Can you imagine putting a bonding connector in a one gang old work gem box? lol
 
For MC cable, the armor is not an EGC, there is a green EGC for that. MP-AP uses the armor for an EGC.
So MC cable could be used with the appropiate plastic box but MC-AP could not
 
tom baker said:
For MC cable, the armor is not an EGC, there is a green EGC for that. MP-AP uses the armor for an EGC.
So MC cable could be used with the appropiate plastic box but MC-AP could not
Click to expand...

I thought MC-CAP used the armor as an EGC in addition to a wire conductor in the metallic sheath, so If one did not need a redundant(second) EGC what would be the harm of using the wire conductor as the EGC and merely bonding the sheath?


Edit: Ooops! Just went to Southwire site, I mixed up MCAP with HCF MC cable.:ashamed1:
 
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raider1 said:
Take a look at 314.3



Chris
Click to expand...
OK, that clarifies things for "boxes" what about non metallic cabinets, non metallic gutters/wireways, or other non metallic enclosures not specifically referred to by NEC as "boxes"?

I know they are a little rare to use with metallic wiring methods, but there are still occasions where it happens.
 
kwired said:
OK, that clarifies things for "boxes" what about non metallic cabinets, non metallic gutters/wireways, or other non metallic enclosures not specifically referred to by NEC as "boxes"?

I know they are a little rare to use with metallic wiring methods, but there are still occasions where it happens.
Click to expand...

Best I can come up with is 312.10(C), the enclosure would have to be listed for a metallic wiring method or approved by the inspector for such.
 
In the event I run into this situation I’ll use a double inlet type mc connector so there is continuous metal contact.
 
mopowr steve said:
In the event I run into this situation I’ll use a double inlet type mc connector so there is continuous metal contact.
Click to expand...
Sorry I'm just now jumping back into this thread that I started. Exception 1 in 314.3 indicates that the bonding has to be "internal". So, I'm guessing that a duplex MC connector is not the correct fitting to use. In Exception 2 I'm guessing that bonding bushings would have to be used in order to continue the MC to another box. Just trying to think "out-of-the-box" here and not trying to bash anyone's ideas.

314.3 Nonmetallic Boxes. Nonmetallic boxes shall be permitted only with open wiring on insulators, concealed knob-and-tube wiring, cabled wiring methods with entirely nonmetallic sheaths, flexible cords, and nonmetallic raceways.

Exception No. 1: Where internal bonding means are provided between all entries, nonmetallic boxes shall be permitted to be used with metal raceways or metal-armored cables.

Exception No. 2: Where integral bonding means with a provision for attaching an equipment bonding jumper inside the box are provided between all threaded entries in nonmetallic boxes listed for the purpose, nonmetallic boxes shall be permitted to be used with metal raceways ormetal-armored cables.
Click to expand...
 
I think that the intent is to have maintain ground connection of the metallic raceway when a plastic box usually insulates between two ko’s. A dual fitting aleiviates that.
 
goldstar said:
... I've been told by a CEU instructor that it is Code compliant to terminate MC cable in plastic JB's.
Click to expand...

That's more of a trivia question or something you may find on a test, something to keep in the back of your mind. As has been noted, yes, it is allowed subject to exceptions but in the real world such instances should rarely exist if the work is done properly.

goldstar said:
The reason I'm asking this is an EC friend of mine questioned me because he is wiring a residential garage and is concerned that rodents will chew through NM cable.
Click to expand...

So he doesn't know where to buy steel boxes anymore? That's what I'm talking about when I say "if the job is done right".

-Hal
 
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