MC cable question

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guschash

Senior Member
Location
Ohio
I'm putting in a 4-way switch and I want to use MC cable but I need to get a neutral to one of the 3-ways. Is it code compliant to run the MC cable and just cap off the black conductor at each end?
 

LEO2854

Esteemed Member
Location
Ma
I'm putting in a 4-way switch and I want to use MC cable but I need to get a neutral to one of the 3-ways. Is it code compliant to run the MC cable and just cap off the black conductor at each end?

If you are using 3 wire you'll need the black wire, considering that black and red are your travelers, your white is the neutral and your green is your EGC...

You may be over-thinking this, draw it on paper..:D
 

iwire

Moderator
Staff member
Location
Massachusetts
I'm putting in a 4-way switch and I want to use MC cable but I need to get a neutral to one of the 3-ways. Is it code compliant to run the MC cable and just cap off the black conductor at each end?

You want to run a second MC cable just for the neutral?

If so no, all circuit conductors must be contained in the same armor. See 300.3(B)
 

guschash

Senior Member
Location
Ohio
Yes second cable just for neutral. At one 3-way , I will have the cable that goes to the light , and I will send one cable to the 4-way for the travelers and from there to other 3-way but I need a neutral at the first 3-way for the neutral for the lights. The last 3-way will have the power coming in and the neutral which I need to get to first 3-way for the lights.
 

guschash

Senior Member
Location
Ohio
I'm just going to use MC 12-2-2. Black, Red, white , green. I didn't think my supply house had it in stock but they do. Thanks for replies.

Gus
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
. . . a neutral at the first 3-way for the neutral for the lights. The last 3-way will have the power coming in and the neutral which I need to get to first 3-way for the lights.
Assuming that you are using 12/2 and 12/3 MC cables:
1. 12/2 brings power to a (you call it the "last 3-way") threeway switch, black goes to Common on the switch
2. 12/3 leaves "last 3-way" to go to the 4-way, red and black are used as travelers and the white is the neutral
3. At the 4-way switch, the red and black connect to the switch, and the 12/3 white (the neutral) ties to the next 12/3 that goes from the 4-way switch to the "first 3-way" switch and, again, the red and black are the travelers.
4. 12/3 arrives at the "first 3-way (as you call it)" bringing the neutral needed for the lights, the 12/3 red and black connect to the threeway switch traveler terminals and the Common connects to the 12/2 black that goes to the lights. The whites are tied together, as they are the neutral you need for the lights.

I agree with Leo, it sounds like you are over thinking this one.

12/2-2 will give you an extra, second, neutral that you don't need.
 

kwired

Electron manager
Location
NE Nebraska
Should you need a "hot" as well as the neutral at the end switch for some reason, then you will need extra conductor in the cable otherwise standard black, red, white, green will work if you hit one end with power and go to the load off the other end of the switching circuit.


Not only is it a code violation to run just a single conductor in a raceway or cable as earlier suggested, it creates bigger issues if it is steel raceway or jacket on the cable, as you will have inductive heating effects on that steel because there is no conductor carrying opposing current to cancel magnetic effects.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Should you need a "hot" as well as the neutral at the end switch for some reason, then you will need extra conductor in the cable otherwise standard black, red, white, green will work if you hit one end with power and go to the load off the other end of the switching circuit.


Not only is it a code violation to run just a single conductor in a raceway or cable as earlier suggested, it creates bigger issues if it is steel raceway or jacket on the cable, as you will have inductive heating effects on that steel because there is no conductor carrying opposing current to cancel magnetic effects.
But if the neutral in a section of two wire (plus ground) MC is used only to carry the return current from an occupancy detector, the inductive heating and other effects will be trivial. Still a code violation though.
 

kwired

Electron manager
Location
NE Nebraska
But if the neutral in a section of two wire (plus ground) MC is used only to carry the return current from an occupancy detector, the inductive heating and other effects will be trivial. Still a code violation though.

That is correct.

It will also upset the EMF police, that have no tolerances at all of what EMF's are acceptable:happyyes:
 

darekelec

Senior Member
Location
nyc
What if somebody wired 4 way switch with 12/3 and then realized he needs neutral to satisfy that new 2011 code but he is not using the neutral so he does not violate 300.3 (B).
Than next contractor tries to install motion sensor with neutral and he is at violation of 300.3 b.
Would this scenario cover the first contractor?
 

kwired

Electron manager
Location
NE Nebraska
What if somebody wired 4 way switch with 12/3 and then realized he needs neutral to satisfy that new 2011 code but he is not using the neutral so he does not violate 300.3 (B).
Than next contractor tries to install motion sensor with neutral and he is at violation of 300.3 b.
Would this scenario cover the first contractor?
That one is a little trickier. If the initial install was supposed to comply with 2011, then it really was wrong from the start. But the second contractor adding the motion sensor that requires a neutral conductor still was wrong to install it if there is no neutral to connect it to or at least needs to install a proper neutral first, IMO.
 
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