Multi-Wire Branch Circuit - Common Neutral

[Dyno Dan]

I started wiring my pole barn and have a few questions. **In the interest of disclosure, electrical work is not my thing. I’ve done some typical home owner stuff, ie replaced outlets, switches,etc etc, so I’m a little green in regards to experience. That being said I hired an electrician to run a 100 amp power service to my new building from an existing 200 amp panel. Since then I haven’t had much luck getting anyone back out here to run circuits for me.....so I’m going it alone”

Picture of the panel:



General layout:



My father-in-law talked me into running 12/3 (3 conductors and a ground) to have flexibility to run another circuit. I did so and my Intent is to have a multi wire branch circuit.....at least that’s what I think they call it . The first circuit will have six outlets on it (black wire) over on the open side of the shop on back and side wall, while the other circuit I intend to have switched power for the lights (on red wire) over on the same side / open side of the shop. In this configuration I would have to share the neutral. I have a junction box to breakout the 2 circuits.

That all seems straightforward but here’s where I need some help. What’s the best way to run a switch for the light circuit? I could double back from my junction box and drop 12/2 down to a switch and then back out of the box and to the lights. Is there simply a way to wire the lights in series and then and at the light switch?

Lastly where the two circuits enter the panel it appears that I would need a GFCI 2 pole 20 amp that has a tie bar. Aren’t 2 poles typically 208/240v? I believe that’s the trick here, where the black wire is getting 110 V and the red wire is getting 110 V and sharing a common neutral to balance the load.....am I thinking about that right?

Hopefully some of this made sense. Looking forward to thoughts and comments.

 

[jeffmattero76]

Not an electrician, but do lots of electrical work on my rental properties.

To your first question... current code requires a neutral at all switch locations. Therefore, bringing power to the light fixture first, and then running a switch loop to the switch, is no longer allowed.


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[pattenp]

Your father-in-law led you astray. MWBC's are not worth the trouble to save on one neutral conductor. A MWBC is in essence a 120/240V circuit and requires a 2 pole breaker. Plus having to have GFCI for the outlet side you now have to use a GFCI 2 pole breaker because of the shared neutral. If it's not too late dump the MWBC and go with individual circuits and use a GFCI outlet to protect the outlet circuit.

P.S. Keep lighting and outlets on separate circuits.

 

[pattenp]

Not an electrician, but do lots of electrical work on my rental properties.

To your first question... current code requires a neutral at all switch locations. Therefore, bringing power to the light fixture first, and then running a switch loop to the switch, is no longer allowed.


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Not totally true. There are provisions if a neutral can be added later without much trouble or having to dismantle the structure to do so.

 

[jeffmattero76]

Your father-in-law led you astray. MWBC's are not worth the trouble to save on one neutral conductor. A MWBC is in essence a 120/240V circuit and requires a 2 pole breaker. Plus having to have GFCI for the outlet side you now have to use a GFCI 2 pole breaker because of the shared neutral. If it's not too late dump the MWBC and go with individual circuits and use a GFCI outlet to protect the outlet circuit.

Just trying to educate myself... if he came out of the panel with 12/3 to a Junction box, why could he not split the circuit at that Junction box and run 12/2 from there to a GFCI for the receptacle run, and another run of 12/2 to the lights?

I guess my main question is, doing as I described, would he be required to use a 2 pole GFCI breaker, or would he be allowed to use a regular 2 pole breaker?

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[pattenp]

Doing as you describe using a regular 2 pole breaker will work as long as the GFCI outlet is down stream of a shared neutral. If you trip the outlet circuit you also loose the lights using a 2 pole common trip breaker so it's better to use independent single pole breakers with a handle tie so one circuit tripping doesn't take out the other circuit.

 

[jeffmattero76]

Doing as you describe using a regular 2 pole breaker will work as long as the GFCI outlet is down stream of a shared neutral. If you trip the outlet circuit you also loose the lights using a 2 pole common trip breaker so it's better to use independent single pole breakers with a handle tie so one circuit tripping doesn't take out the other circuit.

Thanks. One more question... what 8s the purpose of a handle tie if not to shut off BOTH breakers if one if them were to trip? I always thought that was the whole point of the handle tie.

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[pattenp]

Do you have a ufer or ground rods for the grounding electrode system?

 

[jeffmattero76]

Do you have a ufer or ground rods for the grounding electrode system?

???

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[pattenp]

The handle tie is required for servicing so that power is turned off to both legs when working in that junction box where both hots are accessed. The handle tie is not so both legs trip when one trips. The common trip is only required when there are line-to-line loads (240V), loads are only to be Line-to-Neutral when using independent trip single pole breakers with a handle tie..

 

[mm08822]

I would not use a mwbc for lighting and recepts b/c a 2 pole cb is required for this wiring method. If the recepts trip the cb, then you lose the lights also.

Having a lighting/recept layout is step 1.

• Looking at your plan, you may want more recepts near the garage doors on the left side and front wall – corners have nothing.
• Lighting – how did you arrive at this layout?
• Only one switch location? Several feet inside?
• How many switches for lighting in each bay?
• Is there a man door anywhere? Would need switch(es) just inside of it. If no door, how do you get into bldg when power is off?

Step 2 is planning how to wire everything shown in step 1 – conduit routing, conduit fill, circuit allocation, etc. Or choose cable, but then you are back to exposure to damage. Conduit is the cleaner install.

 

[pattenp]

???

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Your pole barn needs a grounding electrode system. Ufer or two 8' ground rods with a #6 grounding conductor run to the subpanel.

 

[mm08822]

???

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Do you have a ufer or ground rods for the grounding electrode system?

OP already answered in another thread that the electricians helpers didn't install the 2 rods and there was no ufer. It was suggested he get them back to complete this.

 

[pattenp]

I would not use a mwbc for lighting and recepts b/c a 2 pole cb is required for this wiring method. If the recepts trip the cb, then you lose the lights also.

Using two single pole breakers and a handle tie takes care of that problem.

 

[egdede]

Use the double pole breaker, they are both supposed to trip if either does. Tie handles still trip the other breaker, that is why they are tied together, If one trips and the other doesn't, then they are not tied together properly (the tie bar is too loose).

Pig tail all neutral connections (make sure outlets and switches can be removed without breaking the neutral path.

As others have said; the lights will go if you trip the power side of that MWBC.

 

[Dyno Dan]

Just trying to educate myself... if he came out of the panel with 12/3 to a Junction box, why could he not split the circuit at that Junction box and run 12/2 from there to a GFCI for the receptacle run, and another run of 12/2 to the lights?

I guess my main question is, doing as I described, would he be required to use a 2 pole GFCI breaker, or would he be allowed to use a regular 2 pole breaker?

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Thanks for the replies everyone. I’ve been reading this on the girls so excuse me if I miss any questions.

The 12/3 that runs from the panel to the a junction box, and then 12/2 down to some outlets where the first outlet has a GFI outlet. The other circuit/red wire is simply capped up in the junction box.

I have not yet added a grounding rod to the panel inside the new shop. As shown in a different post, there is a proper grounding rod at the service panel where the power comes from for this new service.

In regards to the layout, it was a quick and dirty sketch up. There is a man door at the partition wall. My intent was to have light switches just inside this door, one for the open bays and one for the enclosed side. I may end up with another few switches for carriage lights, a floodlight on the front, and the floodlight on the back of the building.

Also I am all ears in regards to the lighting layout. Still looking at some of the information available in regards to fixtures and LED tubes.

 

[Dyno Dan]

Here’s some perspective on the building and layout. Don’t mind the heavy black lines in back right corner, that’s another project for another day.

 

[pattenp]

Use the double pole breaker, they are both supposed to trip if either does. Tie handles still trip the other breaker, that is why they are tied together, If one trips and the other doesn't, then they are not tied together properly (the tie bar is too loose).

Pig tail all neutral connections (make sure outlets and switches can be removed without breaking the neutral path.

As others have said; the lights will go if you trip the power side of that MWBC.

This is not correct. Single pole breakers that I have put a handle tie on do not trip both breakers when one is tripped. The breaker trips internally and the handle does not have any force to pull the second breaker's handle over. The reason for having the handle tie on a MWBC when it's a line-to-neutral only circuit is to disconnect both legs when servicing. Common trip double pole is only required when the MWBC is serving line-to-line loads where on an overload both legs need to trip. You are confusing disconnecting means vs. overcurrent protection. NEC 210.4 240.15(B)

 

[theoldwizard1]

I assume the red hand drawn line is your 12/3. If it is already installed you may not be able to do this.

Install a J-box on wall near the door. Split the red and the neutral. Run 12/3 from the J-box to your switch by the door. The neutral won't be used except in the switch box, except in special circumstances.

Actually, I would have started the daisy chain for the lights at the light closest to the door so that long run of 12/3 to the back wall was not needed. Also lighting circuits almost NEVER need to be 12 gauge/20A.

 

[egdede]

This is not correct. Single pole breakers that I have put a handle tie on do not trip both breakers when one is tripped. The breaker trips internally and the handle does not have any force to pull the second breaker's handle over. The reason for having the handle tie on a MWBC when it's a line-to-neutral only circuit is to disconnect both legs when servicing. Common trip double pole is only required when the MWBC is serving line-to-line loads where on an overload both legs need to trip. You are confusing disconnecting means vs. overcurrent protection. NEC 210.4 240.15(B)

Have to say, I learned something new. although, it appears that only some single pole breakers can be handles tied together: http://www.mikeholt.com/download.php?file=PDF/HOLT_Labels_101_Slash_20120906.pdf

 

[Toomanytools?]

So just to throw this out there, "Permit" ? If you had an electrician hook up service did he pull a permit? Usually a basic shop install is a light switch by the man door to light up near panel, an exterior light over man door entry and a GFCI outlet near the panel. If you have that and get signed off for final then you can finish your wiring. Though the work done after that final still needs a permit and inspection.
What I'm getting at is if you are finishing up on electricians permit you might have some issues. Not trying to get into a whole permit thing , just hate to see you do a bunch of work then hit a road block.

 

[pattenp]

Have to say, I learned something new. although, it appears that only some single pole breakers can be handles tied together: http://www.mikeholt.com/download.php?file=PDF/HOLT_Labels_101_Slash_20120906.pdf

Typically all residential use single pole breakers I'm aware of have the "slash" rating 120/240 and can be used with handle ties on MWBC line-to-neutral loads.

 

[mm08822]

Thanks for the replies everyone. I’ve been reading this on the girls so excuse me if I miss any questions.

The 12/3 that runs from the panel to the a junction box, and then 12/2 down to some outlets where the first outlet has a GFI outlet. The other circuit/red wire is simply capped up in the junction box.

I have not yet added a grounding rod to the panel inside the new shop. As shown in a different post, there is a proper grounding rod at the service panel where the power comes from for this new service.

In regards to the layout, it was a quick and dirty sketch up. There is a man door at the partition wall. My intent was to have light switches just inside this door, one for the open bays and one for the enclosed side. I may end up with another few switches for carriage lights, a floodlight on the front, and the floodlight on the back of the building.

Also I am all ears in regards to the lighting layout. Still looking at some of the information available in regards to fixtures and LED tubes.

To meet code in the garage you still need 2 grd rods connected to the gnd bar in the garage sub-panel. The grd rod at the house main panel does not satisfy the additional requirement for the detached garage.

You're good with the switches just inside the door. I didn't realize the 3 bays were open and the "partition" door is an exterior door.

For lighting layouts, provide the following details and you will get some good recommendations from PlatonicSolid:

• Purpose - what you plan on doing/needing the space for - e.g. storage, surgery....
• ceiling height
• wall finish, floor finish, ceiling finish
• type of fixture chosen/preferred
• lighting "color temperature"
• Coldest wintertime temp

 

[Dyno Dan]

No permit. I live out in the sticks, and although that's not a good answer for not getting a permit, I did hire a licensed electrician to do the work and would have expected a permit to be pulled. In all fairness they hooked up the 250 MCM at the 200 amp panel, laid it in a trench, backfilled the trench by hand for the first few inches, and then hooked up the wires at the new panel. As mentioned in a previous post there is NOT a ufer or grounding rods. There is currently an outlet off the bottom of the panel with a 2 gang box with 2 GFI outlets that were repurposed from the other panel.

 

[Dyno Dan]

To meet code in the garage you still need 2 grd rods connected to the gnd bar in the garage sub-panel. The grd rod at the house main panel does not satisfy the additional requirement for the detached garage.

You're good with the switches just inside the door. I didn't realize the 3 bays were open and the "partition" door is an exterior door.

For lighting layouts, provide the following details and you will get some good recommendations from PlatonicSolid:

• Purpose - what you plan on doing/needing the space for - e.g. storage, surgery....
• ceiling height
• wall finish, floor finish, ceiling finish
• type of fixture chosen/preferred
• lighting "color temperature"
• Coldest wintertime temp

On the enclosed side:
* general workshop, auto and toy tinkering / repair
* 12' ceiling
* wall finish is up in the air, plan on concrete (currently #3 road mix), white metal ceiling liner in place already
* not sure on fixtures......open to suggestions
* not sure on lighting "color temps"
* winter ambient temps will be down to -30 deg F, although this side will probably be kept no cooler than 42 degrees.

On the open / 3 sided side:
* parking for equipment
* 12' ceiling
* currently have 4' of OSB acting as a "bash board and it's open / exposed above that, currently #3 road mix will will likely stay that way, white metal ceiling liner in place already
* not sure on fixtures......open to suggestions
* not sure on lighting "color temps"
* winter ambient temps will be down to -30 deg F

 

[Dyno Dan]

Also, to be clear, I have NO problem running 12/2 (or something "lighter") over to the open side of the shop for the light circuit. I can easily leave the 12/3 in place with the wire nut on the red wire and tucked inside the J-box. Yes wasteful but live and learn......every day. On 2 of the posts on the open side / front side I also intend on dropping 2 points of service in weatherproof boxes. These would be independent 20a services for engine block heaters (John Deere 5085m and 1025R). I think the big tractor has a 1500 watt heater. Sure I could use the receptacle behind the tractor, but thought it would be nice to have a couple outlets on the front side of the building (open / exit side).

Image for perspective.....although not current. I need some new pics.

 

[Dyno Dan]

I spoke with the electrician this evening about the need for a ground at the new panel. He said it is not necessary since the ground is carried all the way from the new panel to the supply panel, where it’s properly grounded at that point.

He did advise against running the 12/3 to 2 separate circuits (MWBC) and sharing a neutral. He said that code changed about four years ago and with all of the LED lights and such that the potential for issues is higher.....If I heard him right. That being said I will carry-on with 12 two for each circuit.

Also thought I would share an exterior pic looking straight on for additional reference.

 

[mm08822]

I spoke with the electrician this evening about the need for a ground at the new panel. He said it is not necessary since the ground is carried all the way from the new panel to the supply panel, where it’s properly grounded at that point.

Just to be clear, we are talking about the grounding electrode system and grounding electrode conductor. Not the equipment grounding conductor.

He is wrong and needs to read NEC 250.32. i've attached the NEC article and an illustration for you.

 

[pattenp]

The grounding electrode system is to help divert lighting strikes to the earth if the strike occurs at the detached structure. You don't want that strike traveling on the equipment ground conductor back to the main panel if possible.

 

[Dyno Dan]

Makes complete sense, and thanks for the graphic....that’s helpful. What can I say, I hired a licensed professional, even questioned him on this subject months after, and here I am.

pattenp - you mentioned earlier I need (2) 8’ ground electrodes at my new building? Looking at my house and other detached shop they appear to only have 1 each?

 

[pattenp]

NEC only requires one rod if resistance is 25 ohms or less to earth which requires expense to prove so it's more economical to just drive two rods to satisfy the resistance requirements.

 

[Dyno Dan]

On the enclosed side:

* general workshop, auto and toy tinkering / repair

* 12' ceiling

* wall finish is up in the air, plan on concrete (currently #3 road mix), white metal ceiling liner in place already

* not sure on fixtures......open to suggestions

* not sure on lighting "color temps"

* winter ambient temps will be down to -30 deg F, although this side will probably be kept no cooler than 42 degrees.



On the open / 3 sided side:

* parking for equipment

* 12' ceiling

* currently have 4' of OSB acting as a "bash board and it's open / exposed above that, currently #3 road mix will will likely stay that way, white metal ceiling liner in place already

* not sure on fixtures......open to suggestions

* not sure on lighting "color temps"

* winter ambient temps will be down to -30 deg F

Any comments on lighting guys? I’d love to hear recommendations for surface mount LED lights on both the enclosed and open side. Also the wire requirements for both sides (will 14/2 be adequate to fire up all lights in each area?)

 

[teamextreme]

Looking at my house and other detached shop they appear to only have 1 each?

Many years ago it was allowed to install only one.

 

[Dyno Dan]

NEC only requires one rod if resistance is 25 ohms or less to earth which requires expense to prove so it's more economical to just drive two rods to satisfy the resistance requirements.

Does the copper wire need to be in conduit where it enters the panel? I have a 90 degree 1.75” elbow under the base / skirt board and a short (25”) of 1.75” conduit run into my “electrical panel area”. Can the copper ground wire exit the conduit and then be stapled / secured the wood backing before entering a knock out.

I need to get a pic quick. The more I think about it, I should probably reduce the 1.75” down to something that can enter the panel “cleanly”.

 

[pattenp]

The grounding electrode conductor does not have to be in conduit.

 

[Dyno Dan]

The grounding electrode conductor does not have to be in conduit.

Thanks. I still may clean it up and move it over to the right, where a larger knockout exists.

 

[Dyno Dan]

I’ve wired the west wall with (5) outlets, and the back wall with (7) outlets. The back wall is where I intend to have a work bench. I still need to wire up my east wall. Also intend to run a 30 amp service for a compressor and perhaps another for a welder.

 

[Dyno Dan]

Got light! I hung 6 lights using “riv-serts” so I could flush mount the fixtures directly to the steel ceiling liner.

*I can’t seem to post pics right now*

 

[Dyno Dan]

Here we go.

 

[Dyno Dan]

Added some carriage lights, a motion sensitive wall pack, LED floodlight, and some Liftmaster 8500W garage door operators.