Mc wiring and pvc boxes

Status
Not open for further replies.
L

Luke S

Member
Location
Thomson
Occupation
Electrician
New to the forum but have a question that has been brought up on an Mc installation I found in commercial building. I found Mc installed in standard Carlon single gang cut in box thru NM cable inlet with no connector. Is this permissible and if so where in nec does it allow it. I found where Mc can be used in listed pvc boxes 314.3 but also found where terminations on Mc cable must have listed connector 330.40. It is a discussion my coworkers and I are having.
 
I think some things have changed from year to year, but I think the intent has been about the same. Here’s what it says in 2017. Would need connectors identified for use with MC:

———
330.6 Listing Requirements. Type MC cable shall be listed.
Fittings used for connecting Type MC cable to boxes, cabinets,
or other equipment shall be listed and identified for such use.
 
That was my thought too, there is nothing to secure the wire in box or protect the conductors from the sharp edges of mc jacket.
 
I believe it is covered by NEC 314.3 Exception.
(difficult if not impossible with MC connectors_)
 
Luke S said:
So my main question is connectors are not always required on mc cable?
Click to expand...
Installation instruction (AFC Cable) seem to indicate a fitting is required:
Terminating AC & traditional MC Cables
When terminating or splicing at a junction, outlet or switch box, cut
the cable so that 6 inches of free conductor is left for connections
or splices.
Use an approved connector and insure a proper bond by
firmly tightening the connectors to both the box and the cable.
Please note: set screw connectors cannot be used with aluminum
armor Type AC cable. To terminate an AC cable, insert an anti-short
bushing and bend back the exposed length of bonding wire. The
bonding wire can be bent back before or after the bushing is
inserted. There are several techniques used for this procedure as
pictured on the next page.
 
Thank you, this was my thought from the beginning and the only way I have ever installed. I just have one customer that knows everything about everything and has never done electrical work in his life.
 
Luke S said:
Thank you, this was my thought from the beginning and the only way I have ever installed. I just have one customer that knows everything about everything and has never done electrical work in his life.
Click to expand...
We have some of those here too
 
Even though the armor of MC is not used for the EGC (like AC cable) it still must be grounded. That just doesn't happen with a plastic box designed for NM. This is why connectors are needed to secure MC and AC to steel boxes and why only steel boxes are normally only used with those cables.
Luke S said:
I found where Mc can be used in listed pvc boxes 314.3
Click to expand...

I know of no listed boxes suitable for use with MC or even AC cables. I suppose with a PVC J box you could use connectors listed for MC and a grounding bushing on the inside, then bond them all together to the EGC. But why would you use a PVC box with a metallic wiring system anyway?

-Hal
 
In a gutted remodel with plastic boxes and NM, I used one metal box for the switch for an existing BX cable to an outside light, embedded in the masonry. That was the simplest way to bond the sheath.
 
Status
Not open for further replies.
Top