12/2 or 12/3

[mstrlucky74]

How would this most commonly be wired in the field? Would 12/3 be dropped down the wall and pick up ckt 55 & 57 or 12/2 down to each 55 and 57? Why one way over the other? You would have to splice through with the 12/3 . Thanks

 

[infinity]

A 12/3 would indicate a MWBC which would require you to use a 2-pole breaker or two single poles with a handle tie. Might not be the best design option.

 

[mstrlucky74]

A 12/3 would indicate a MWBC which would require you to use a 2-pole breaker or two single poles with a handle tie. Might not be the best design option.

Right, cause you would be sharing a neutral and that wouldn't make sense because your home run would contain separate neutrals(most common way, not handle ties). Think I got it.

 

[peter d]

In a perfect world without the ridiculous rule for handle ties to protect the unqualified, I would run MWBC's all day long.

 

[infinity]

In a perfect world without the ridiculous rule for handle ties to protect the unqualified, I would run MWBC's all day long.

I agree, nothing like wasting copper with individual neutrals. :rant:

 

[don_resqcapt19]

I agree, nothing like wasting copper with individual neutrals. :rant:

And the increased I²R losses for the individual neutrals over the life of the installation.

 

[Greg1707]

qualified personnel

qualified personnel

In a perfect world without the ridiculous rule for handle ties to protect the unqualified, I would run MWBC's all day long.

When doing repair work or adding circuits in a large panel with multiple conductors run in conduit, how do qualified workers identify MWB?

 

[iwire]

When doing repair work or adding circuits in a large panel with multiple conductors run in conduit, how do qualified workers identify MWB?

A meter, an amp clamp, a tracer, skill.

How did they do it for a 100+ years?

 

[electrofelon]

When doing repair work or adding circuits in a large panel with multiple conductors run in conduit, how do qualified workers identify MWB?

Note that the purpose of the multi pole/ handle tied breaker is not for identifying the conductors of a mwbc.

 

[peter d]

When doing repair work or adding circuits in a large panel with multiple conductors run in conduit, how do qualified workers identify MWB?

Hopefully the original installer paired the neutral off with the phase conductors in accordance with existing NEC rules. Barring that, it would require tracing the circuit.

This is standard electrical work that qualified, competent commercial electricians do every day or every week. I am completely against the continual dumbing down of the trade and rule making to protect the dumb.

 

[ActionDave]

Hopefully the original installer paired the neutral off with the phase conductors in accordance with existing NEC rules. Barring that, it would require tracing the circuit.

This is standard electrical work that qualified, competent commercial electricians do every day or every week. I am completely against the continual dumbing down of the trade and rule making to protect the dumb.

You and me both, but the battle is going to be won by the other side. The NEC won't stop dumbing down our trade because it's the only thing the authors have left to do to feel important. I hate 210.4(B) so much that it is one of the few references I know by heart. It's not going away and that is sad on so many levels.

 

[peter d]

You and me both, but the battle is going to be won by the other side. The NEC won't stop dumbing down our trade because it's the only thing the authors have left to do to feel important. I hate 210.4(B) so much that it is one of the few references I know by heart. It's not going away and that is sad on so many levels.

I agree. The NEC gets worse every cycle in that regard. The only rule I detest even more than AFCI's is the handle tie rule for MWBC's. That's a blatant capitulation to protecting unqualified people.

 

[chris1971]

How would this most commonly be wired in the field? Would 12/3 be dropped down the wall and pick up ckt 55 & 57 or 12/2 down to each 55 and 57? Why one way over the other? You would have to splice through with the 12/3 . Thanks

I'd run 12-3 as a MWBC. Does the job have specs that state you can't use mwbc's?

 

[jaggedben]

When doing repair work or adding circuits in a large panel with multiple conductors run in conduit, how do qualified workers identify MWB?

If it's cable then you can tell from which wires go into the cable. If not then they are required to be grouped with other means (wire ties or tape). Personally I think the grouping is a heck of a lot more important than the handle-ties; handle ties don't help you identity the neutral.

 

[user 100]

I agree. The NEC gets worse every cycle in that regard. The only rule I detest even more than AFCI's is the handle tie rule for MWBC's. That's a blatant capitulation to protecting unqualified people.

Unfortunately the reliable and safe Edison circuit will probably end up going the way of the dodo bird.

Probably have apprentices asking here several cycles from now about what a mwbc even is.:happysad:

I agree w/ Chris1971 about the mwbc and 12/3.

 

[ActionDave]

Unfortunately the reliable and safe Edison circuit will probably end up going the way of the dodo bird.

And probably within the next twenty years.

Probably have apprentices asking here several cycles from now about what a mwbc even is.:happysad:....

I can hear the conversation, "You're crazy old man. How do you get three circuits only using four wires? You need six."

 

[infinity]

If it's cable then you can tell from which wires go into the cable. If not then they are required to be grouped with other means (wire ties or tape). Personally I think the grouping is a heck of a lot more important than the handle-ties; handle ties don't help you identity the neutral.

You can also individually number the conductors to avoid the grouping requirement which in a packed panel is a better solution.

 

[jaggedben]

I'd rather just have them grouped where they come out of the conduit.

 

[peter d]

I agree, nothing like wasting copper with individual neutrals. :rant:

And the increased I²R losses for the individual neutrals over the life of the installation.

Eliminating wasted copper and losses and saving labor...these are all sacrificed for the sake of unskilled, untrained people who might encounter and tamper with a MWBC. The code really is made by people who are disconnected from reality.

 

[peter d]

Unfortunately the reliable and safe Edison circuit will probably end up going the way of the dodo bird.

Probably have apprentices asking here several cycles from now about what a mwbc even is.:happysad:

I agree w/ Chris1971 about the mwbc and 12/3.

Sadly, I've found even supposedly skilled electricians who are afraid to use MWBC's. :roll:

Back when I was wiring new houses in 1999/00 before the dawn of the AFCI, we would run tons of 3-wire circuits throughout the house. Those were the days.