Terminating EGC's when using 12/2 MC

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goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I'm helping out a fellow contractor and doing some re-wiring at a high rise condo. It's a fairly new building and the original branch circuit wiring was done with 12/2 AC. We are now adding receptacles and lighting to existing circuits and are using 12/2 MC. My friend's contention is that we do not have to bond the green wires to the JB's, the spiral aluminum jacket on the MC takes care of that. My contention is that the aluminum jacket is not an effective ground path and the MC should be grounded via the green wires. There are no situations where isolated grounds are required and all receptacles are self-grounding.

We are also not using any red heads. I know we've had this discussion in the past regarding red heads and MC cable but if it were my job I would use them just as a precaution.

Any thoughts would be appreciated. Thanks.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
I'm helping out a fellow contractor and doing some re-wiring at a high rise condo. It's a fairly new building and the original branch circuit wiring was done with 12/2 AC. We are now adding receptacles and lighting to existing circuits and are using 12/2 MC. My friend's contention is that we do not have to bond the green wires to the JB's, the spiral aluminum jacket on the MC takes care of that. My contention is that the aluminum jacket is not an effective ground path and the MC should be grounded via the green wires. There are no situations where isolated grounds are required and all receptacles are self-grounding.

We are also not using any red heads. I know we've had this discussion in the past regarding red heads and MC cable but if it were my job I would use them just as a precaution.

Any thoughts would be appreciated. Thanks.


You are correct for standard MC, but both Southwire and Encore have a product Southwire is MCAP That doesn't require the grounds to be terminated when used with listed connectors and subject to other grounding requirements in the code regarding concentric knockouts etc. But, this product doesn't have a green wire so, again you are correct for you application.
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
OK....a few things...

1) Encores version is called MC SmartGround or MC SG for short. The outer metallic sheathing does meet the requirements as an equipment grounding conductor per 250.118(10)(b) by adding the 10 AWG AL bonding conductor to the product that makes intimate contact with all of the convolutions.

2) In the SmartGround (SG) products you will not find a insulated EGC...the 10AWG AL is a bonding conductor strictly for the metal sheathing to comply with 250.118(10)(b) only, it may be removed at connector termination, where a properly listed MCI-A connector is used.

3) If the fitting is designed correctly and listed for use with the actual MC products, the adding of a bushing is pointless but your choice as they are included with every roll just in case an inspector does not understand the correct code requirements.

In regards to the NM Cable (Nonmetallic-Sheathed Cable), yes the three story limitation was lifted.....but you still have the construction limitations of Type III, IV and V which will in themselves limit the height of the buildings within that construction type. ( See Informative Annex E for more details )
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
OK then, one more thing. The hospital grade version of these MC's rates the outer sheath as explained AND has a green grounding conductor.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
Just to clarify a few things
  • There is no NM being used on this project
  • Branch circuits in all units in the original construction were done with 12/2 AC
  • All framing was done with 3" metal studs and 5/8 sheet rock
  • In cases where there is a demising wall or adjacent to a unit heater walls were double sheet rocked
  • All walls have insulation in them
  • The MC cable that we used was not made by Encore and does not have a bare shunt wire inside the jacket
  • The original JB's used in this construction were std. depth 4" square with 5/8" or 1 1/4" mud rings
Don, Thanks for your reply but I don't think that 250.148 answers my question. Let me see if I can explain this a little better. We added 2 separately switched light fixtures to an existing lighting outlet.
  • We cut a wall open to add another 4" square JB with a 2-gang mud cover above the original
  • We install a 12/2 MC between the original JB and the 2nd JB
  • We run a 12/3 MC from the 2nd JB to the 1st light outlet and a 12/2 MC from the 1st to the 2nd
We now have one green wire inside the original JB and 2 greens inside the 2nd JB. So, my questions are (and I apologize if they seem basic):
  1. Will the armor of the MC we used be considered an effective grounding path between JB's ? My guess is no.
  2. Should the single green wire in JB-1 be bonded to the JB ? My guess is yes.
  3. Should the 2 greens in JB-2 be spliced together with a pig-tail to a green screw in the JB and 2 pig-tails to the new switches ? My guess is yes.
If the answers to my questions are yes I now have the following problem in JB-2 - we have 5 green wires (1 in, 1 out, 1 to the JB and 2 pig-tails to the switches) spliced together with a wire nut, we have 2 whites spliced together with a wire nut, we have 3 blacks (1 in and 2 pig-tails to the switches) with a wire nut and the 2 conductors for the lighting circuits. Seems like an awful lot of wires in such a shallow box. If it were my project I would have used a deeper JB.

What actually happened (and I believe this was improperly done)
  • The 1 green in the original JB was connected to the green screw on the light switch and the switch was installed
  • The 2 greens in the 2nd JB were connected to each of the light switches and the switches installed
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
If you have EGC(s) of the wire type in an enclosure and your are making splices or connections in that enclosure, then 250.148 requires that the EGC(s) of the wire type be connected to the enclosure. (assuming a metallic enclosure)
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
If you have EGC(s) of the wire type in an enclosure and your are making splices or connections in that enclosure, then 250.148 requires that the EGC(s) of the wire type be connected to the enclosure. (assuming a metallic enclosure)
That's the way I understood it. What I've always done on all other similar jobs is take one of the EGC's, skin the insulation back, bond it to the enclosure using a green ground screw and leave a pig-tail to connect any other EGC's. But, I wasn't going to get into a long, drawn out dispute with my friend over this. It was his job. I'm just there to help him out. I made my point that the grounding connection method was not Code compliant and moved on from there to get the job done in the required time allotted. It's his license on the hook - not mine.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Just to clarify a few things
Don, Thanks for your reply but I don't think that 250.148 answers my question. Let me see if I can explain this a little better. We added 2 separately switched light fixtures to an existing lighting outlet.We now have one green wire inside the original JB and 2 greens inside the 2nd JB. So, my questions are (and I apologize if they seem basic):


  1. Will the armor of the MC we used be considered an effective grounding path between JB's ? My guess is no.
  2. Should the single green wire in JB-1 be bonded to the JB ? My guess is yes.
  3. Should the 2 greens in JB-2 be spliced together with a pig-tail to a green screw in the JB and 2 pig-tails to the new switches ? My guess is yes.

Yes to everything 100% correct


If the answers to my questions are yes I now have the following problem in JB-2 - we have 5 green wires (1 in, 1 out, 1 to the JB and 2 pig-tails to the switches) spliced together with a wire nut, we have 2 whites spliced together with a wire nut, we have 3 blacks (1 in and 2 pig-tails to the switches) with a wire nut and the 2 conductors for the lighting circuits. Seems like an awful lot of wires in such a shallow box. If it were my project I would have used a deeper JB.

NEC 314 has a whole section on sizing and counting wires, but basically, you have, 1 green (all count as one period) 2 whites (jumpers aren't counted period) 1 hot, 2 switch legs, and each device counts as two wires for a grand total of 10 wires at 2.25 cu. in. per wire. A standard 1 1/2" box allows only 9 #12 wires, BUT a 5/8" two gang mud ring adds well over the additional capacity for the additional wire. So, you are fine.

What actually happened (and I believe this was improperly done)
  • The 1 green in the original JB was connected to the green screw on the light switch and the switch was installed
  • The 2 greens in the 2nd JB were connected to each of the light switches and the switches installed

Wrong as stated in the first part.

I was the one who brought up the MCAP Sorry if it confused. Until I though about the lack of green wire I was trying to clarify that there are options where the ground doesn't need to terminate in the box. I you case it does period.
 

Greg1707

Senior Member
Location
Alexandria, VA
Occupation
Business owner Electrical contractor
MC Ap and similiar cables to AC

MC Ap and similiar cables to AC

What is the fundamental difference between AC and MC cable? With the #10 bonding strip included in MC ap I do not understand the distinction between these two cables?


Why are MC like fittings not available for AC to avoid using the anti short bushings?

Does MC Ap require special fittings to provide proper bonding to boxes?
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
What is the fundamental difference between AC and MC cable? With the #10 bonding strip included in MC ap I do not understand the distinction between these two cables?


Why are MC like fittings not available for AC to avoid using the anti short bushings?

Does MC Ap require special fittings to provide proper bonding to boxes?

The best thing I can tell you is look up Southwire on the web Some of your question can be answered by the literature. I don't have much experience with AC cable, but I think it is the design of the bonding strip and the testing with the listed connectors that makes it different.
 

electricalist

Senior Member
Location
dallas tx
4 12/2 mc 's is all i put in a 4 sq. if i need more than that i use 4/11. in general if i have the customer open a wall i redo everything so that theres no confusion as to why it was better to open the wall.
 

jeremysterling

Senior Member
Location
Austin, TX
For the OP: Yes, the green wire in the MC must be terminated to the box. Do not cut off, cap or terminate to a device. If you desire, you may terminate the MC's green wire to a splice that is terminated to the box and if necessary connected to EGC's going to devices or other items that require bonding.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
NEC 314 has a whole section on sizing and counting wires, but basically, you have, 1 green (all count as one period) 2 whites (jumpers aren't counted period) 1 hot, 2 switch legs, and each device counts as two wires for a grand total of 10 wires at 2.25 cu. in. per wire. A standard 1 1/2" box allows only 9 #12 wires, BUT a 5/8" two gang mud ring adds well over the additional capacity for the additional wire. So, you are fine.
Granted and I understand about box fill. But, with all the splicing and wire nuts it's still a lot of crap to stuff into one box even with the mud ring.
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
The best thing I can tell you is look up Southwire on the web Some of your question can be answered by the literature. I don't have much experience with AC cable, but I think it is the design of the bonding strip and the testing with the listed connectors that makes it different.
What exactly does the individual want to know about the MC Products. I can answer any technical questions related to those type products from a manufacturers perspective of the product....ask away.
 

Greg1707

Senior Member
Location
Alexandria, VA
Occupation
Business owner Electrical contractor
AC vs MC

AC vs MC

What exactly does the individual want to know about the MC Products. I can answer any technical questions related to those type products from a manufacturers perspective of the product....ask away.

At first glance the differences between AC and MC are:

AC has bonding strip that allows outer sheath to act as equipment ground.
AC does not have an insulated equipment ground.
AC requires the use of insulated bushings.
AC requires appropriate fittings.

MC does not have bonding strip and the outer sheath cannot act as equipment ground.
MC has insulated equipment ground.
MC has special fittings that avoid the use of insulated bushings.

So my questions. If I have a cable with a bonding strip and insulated equipment ground, is that cable AC or MC?
Why are there no fittings available for AC that avoid the use of insulated bushings?
 
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