How to terminate mc stat cable correctly

[LouisianaApprentice]

I've only ran this type of mc on a bout 4-5 jobs so far but my boss says to just cut off the aluminum wire and leave it loose. That can't be right. Before I had cut it at about 3 inches folded it back and pushed it into the clamp and tightened the clamp on to it to ground the box while I'd also screw in a pigtail to the box. What even is the purpose of this wire how do u terminate it. I understand it's a ground for in case the mc breaks somewhere which generally never happens completely but if this bare aluminum is a necessity why is it a necessity for me to put green wire nuts on grounds with a tail and why am I not allowed by inspectors to skin a ground out bare and twist em all together instead of making a joint with a tail.

 

[LarryFine]

I understand it's a ground for in case the mc breaks somewhere . . .

Actually the bare in AC (not MC) is there to prevent the metal spiral from behaving like an inductor during a fault by shorting adjacent turns together, not as an end-to-end EGC like the green in MC.

 

[LouisianaApprentice]

Actually the bare in AC (not MC) is there to prevent the metal spiral from behaving like an inductor during a fault by shorting adjacent turns together, not as an end-to-end EGC like the green in MC.

Ok thanks for the explanation that makes perfect sense now.

 

[texie]

I've only ran this type of mc on a bout 4-5 jobs so far but my boss says to just cut off the aluminum wire and leave it loose. That can't be right. Before I had cut it at about 3 inches folded it back and pushed it into the clamp and tightened the clamp on to it to ground the box while I'd also screw in a pigtail to the box. What even is the purpose of this wire how do u terminate it. I understand it's a ground for in case the mc breaks somewhere which generally never happens completely but if this bare aluminum is a necessity why is it a necessity for me to put green wire nuts on grounds with a tail and why am I not allowed by inspectors to skin a ground out bare and twist em all together instead of making a joint with a tail.

Sorry, but the boss wins this one. The correct way to do this is to cut it off flush. Find your brand and get the docs from their website.
Also, the bare conductor in contact with the armor supplements the armor as the armor by itself is not a valid EGC.

 

[goldstar]

Yes, you can cut off the metal bonding strip (I like to call it a shunt) if that's what the manufacturer suggests. Generally speaking this type MC is often referred to as "hospital grade" MC (if it's marked in green) where there is a redundant ground. In this case the spiral metal casing qualifies as an acceptable ground and the green insulated wire can be used as an isolated ground if required. So, once you terminate this type MC into a metal JB that box is considered grounded. You can use a green ground screw off the back of the JB with a pig-tail to your device and splice the insulated green wires through to other JB's (unless you're using it in a hospital environment where the redundant ground is required).

I generally like to leave about 4" or so of the shunt wire exposed, slide a red-head on the end of the spiral, bend the shunt back and wrap it around the spiral jacket. It also serves to hold the red-head in place.

 

[Strathead]

Actually the bare in AC (not MC) is there to prevent the metal spiral from behaving like an inductor during a fault by shorting adjacent turns together, not as an end-to-end EGC like the green in MC.

Actually there is MC with this feature. Southwire calls it MC_AP Others have different names but I believe the UL listing is MCI-A What we call hospital grade MC has the green wire and the aluminum. And as others stated, the boss is right. First, your connectors, and that includes the clamps in boxes for MC have to carry the MCI-A listing. Then you merely bend the aluminum wire at a 90 degree angle to the MC and cut flush.