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Discussion Starter · #1 ·
just wanted to check on this detail. (if i already asked this, im sorry. I dont recall this detail.)

I have a 12/3 wire ran in the basement. It was rigged up (before i came here) to have a separate 12/2 line ran off each of the two hot lines in the 12/3. Im going to separate those two 12/2 lines off that and have them run as separate lines back to the panel box instead of this 2 is 1 thing they had going on.

The 12/3 line however is already ran and active. So i figured i could leave it where it is. No point in wasting the wire. The line stops above an old work bench, so i figured i could just attach an outlet to each of the hots and have two outlets on two separate hots.. almost like two dedicated lines. (Maybe it is since it will be connected to a 2 pole 20amp breaker? )
(figured id make each hot have a double gang box with one gfic receptacle and one regular receptacle attached. Since apparently basement lines are supposed to be gfci protected now)

What i wanted to confirm is how to wire the neutral and ground wire form the 12/3 to the outlets. Since there are separate hots, one can go to each outlet. But only 1 neutral and ground in the wire. - I assume i could run the wire into a empty box first and just have each outlet have a white and ground wire running form each and attach to the main wire in that box; nutted up?

Red/black: hot
Pink for white neutral
Green: ground
(both the same, just aligned differently)
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Or is there a better way of doing that?
I dont even have plans for those outlets. It just seems a shame to waste what is already there.
 

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Discussion Starter · #3 · (Edited)
The connection is right, not sure about the GFCI working on one neutral
fair point. Hadnt thought of that.

Not sure if that would be an issue or not. If it is, could i try setting up like a normal run? jsut with the 2 hots going one to each outlet instead?
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(Which makes me wonder; on a run, the neutral is all kinda connected through one wire. Even with a gfci in the first outlet position. So if splicing the neutral for gfci is in fact an issue.. why is it an issue but a run isnt?... my minds been a tad stretched today... )
 

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Figure F3 is depicting a multiwire branch circuit meaning a shared neutral and each GFCI is on a separate circuit. It must originate from a double pole breaker where the red and black wires are on opposite phases. This is important to verify. If they're on the same phase, the neutral wire can be overloaded and will not trip the breaker.
 

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Discussion Starter · #7 ·
Figure F3 is depicting a multiwire branch circuit meaning a shared neutral and each GFCI is on a separate circuit. It must originate from a double pole breaker where the red and black wires are on opposite phases. This is important to verify. If they're on the same phase, the neutral wire can be overloaded and will not trip the breaker.
yea, they had a goofy set up. Each of the hots in the 12/3 are on separate 15amp breakers. (One right below the other.) Which ran to some old school disconnect type thing. I can only guess it was used for something like a 30amp water heater at one point in the past.. - But i got a 2 pole 20amp circuit breaker for when i change the 12/3 over.

Im curious now tho.. if it were 2 breakers on the same poll, how would effect/overload the neutral?
 

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yea, they had a goofy set up. Each of the hots in the 12/3 are on separate 15amp breakers. (One right below the other.) Which ran to some old school disconnect type thing. I can only guess it was used for something like a 30amp water heater at one point in the past.. - But i got a 2 pole 20amp circuit breaker for when i change the 12/3 over.

Im curious now tho.. if it were 2 breakers on the same poll, how would effect/overload the neutral?
I think you are asking/mean if the two circuits of a MWBC were on the same LEG.........."

Well the breakers only "measure " the fed hot current" ....so two breakers supplying let's say 2x15 =30 amps...would be placing 30 amps on a neutral that is only sized for 15 (or 20) amps.

Other wise, if the two "circuits were on different legs"... the neutral would only carry the difference in the amperage draw between the two.... not the additive of the two.
 

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Discussion Starter · #9 ·
Well the breakers only "measure " the fed hot current" ....so two breakers supplying let's say 2x15 =30 amps...would be placing 30 amps on a neutral that is only sized for 15 (or 20) amps.
that did have me wondering too, aside from my question you were addressing. The two hots would be double the amps, which i would assume would be to much for the same gauge neutral wire to handle? For a 12/3 youd have two 12's worth or amps going into one 12 neutral..

Other wise, if the two "circuits were on different legs"... the neutral would only carry the difference in the amperage draw between the two.... not the additive of the two.
ok.. i can understand the difference vs the additive. But why does a #/3 attached to two breakers on the 'same leg' become additive and if they are on different legs, it becomes only the difference?
 

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ok.. i can understand the difference vs the additive. But why does a #/3 attached to two breakers on the 'same leg' become additive and if they are on different legs, it becomes only the difference?
The two legs in your panel are 180 degrees out of phase with each other. You can think of one as being (+) and the other (-) even though AC is a bit more complicated than that.

L1 (+120V)
|
|
N (0V)
|
|
L2 (-120V)

So from each side you will have a current of up to 20 amps, but when they meet together, whatever is drawn by both sides will cancel out. (Actually, you can think of it as a series loop through both loads, with 240V across the whole thing). The neutral is there to balance the voltage of both sides at 120 V, so the "net" current, or the difference of the current drawn by each half of the circuit, is what flows on the neutral.

If you put both sides on the same leg, then they are no longer 180 degrees out of phase, both will be either +120 or -120 at the same time, so it's essentially two parallel 120V circuits, the neutral current no longer cancels out and the neutral wire is then responsible for carrying ALL of the current from both sides back to the panel. So you could end up with as much as 40A on the neutral wire.
 

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Sort of the same thing/concept..... Think of "old" code 240 circuits. They were only fed with two "hots".(different legs 180 degrees apart)..no neutral. Why....the two legs "cancel each other, and no neutral is needed.

Same principle/idea with a MWBC.....except the two legs can have different draws with only the difference on their mutual neutral.
 

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Discussion Starter · #13 ·
The two legs in your panel are 180 degrees out of phase with each other. You can think of one as being (+) and the other (-) even though AC is a bit more complicated than that.

L1 (+120V)
|
|
N (0V)
|
|
L2 (-120V)

So from each side you will have a current of up to 20 amps, but when they meet together, whatever is drawn by both sides will cancel out. (Actually, you can think of it as a series loop through both loads, with 240V across the whole thing). The neutral is there to balance the voltage of both sides at 120 V, so the "net" current, or the difference of the current drawn by each half of the circuit, is what flows on the neutral.

If you put both sides on the same leg, then they are no longer 180 degrees out of phase, both will be either +120 or -120 at the same time, so it's essentially two parallel 120V circuits, the neutral current no longer cancels out and the neutral wire is then responsible for carrying ALL of the current from both sides back to the panel. So you could end up with as much as 40A on the neutral wire.
Thats really interesting to know. I never new there was any difference between each slot or leg.
Just to continue the random thought questions here... would that mean a #/3 attached to two breakers, sharing a neuteral, would use more electricity over time then two completely separate #/2 wires each hooked up to a breaker? Since the neutral form the #/3 only carries the difference back vs a #/2 neutral carrying the full current back to the panel. Or does the currenct from the #/2 just meet up with another leg at the panel box and do the same thing there?
 

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Thats really interesting to know. I never new there was any difference between each slot or leg.
Just to continue the random thought questions here... would that mean a #/3 attached to two breakers, sharing a neuteral, would use more electricity over time then two completely separate #/2 wires each hooked up to a breaker? Since the neutral form the #/3 only carries the difference back vs a #/2 neutral carrying the full current back to the panel. Or does the currenct from the #/2 just meet up with another leg at the panel box and do the same thing there?
Actually MWBCs will have slightly less power wasted by voltage drop along the neutral wire since VD is proportional to the current - but in a typical install that amount is so minimal it is negligible either way. Other than that it's the same. The overall power usage is (amps x volts) and it comes out the same no matter how you slice it.

Yes all the neutral currents from branch circuits will combine at the main neutral bar, and a lot of it will cancel out so you are left with the "net" or difference between the two hot legs' current flowing back to the transformer on the neutral service conductor.
 

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Discussion Starter · #15 ·
Yes all the neutral currents from branch circuits will combine at the main neutral bar, and a lot of it will cancel out so you are left with the "net" or difference between the two hot legs' current flowing back to the transformer on the neutral service conductor.
i could be mistaken as its been a couple years now, but a couple years back i started having what looked like electrical surges (to an untrained eye at least). Lost a few items and appliances. Even the cable line started to melt. The cable guy came out to replace part of the line. As soon as he disconnect the cable line (outside near the tele poll), one of the bedrooms had its outlets start throwing sparks and smoking up. Broke the surge protector but it saved the items plugged into it. Scared the hell outa the guy living in the room at the time... ... After far to long and to many ppl and to many calls.. it was traced to an issue with the big 100amp wire that went form the weather head outside to my panel box inside. I 'believe' they said it was a 'lost neutral'. Which i didnt really understand back then. But i guess it would make sense. If the power had no neutral line functioning to go back to the transformer.. it has to go some where. Hence over loads, and using the cable line to get back to the tele poll.
Either way... i learned real quickly that i dont want a broken/non functioning/non optimal functioning.. neutral wire.
 

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Discussion Starter · #16 ·
Back to the original question about the 12/3.
So the set up in the first pic would work; using a empty box to splice the neutrals together and the grounds together.
Would the set up in the 2nd pic work? Just going straight to the first outlet and setting it up like a run; just using a separate hot for the second box?
If both are good; are there any upsides/downsides to one set up over the other?

Almost forgot to add.. each of the two outlet boxes would be a double gang (2 receptacles). So i guess within the box it is a mini run setup anyway... So i would guess that both set ups could work. Tho i dont like guessing in electrical work'
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Back to the original question about the 12/3.
So the set up in the first pic would work; using a empty box to splice the neutrals together and the grounds together.
Would the set up in the 2nd pic work? Just going straight to the first outlet and setting it up like a run; just using a separate hot for the second box?
If both are good; are there any upsides/downsides to one set up over the other?

Almost forgot to add.. each of the two outlet boxes would be a double gang (2 receptacles). So i guess within the box it is a mini run setup anyway... So i would guess that both set ups could work. Tho i dont like guessing in electrical work'
View attachment 694092 View attachment 694093
No problem splicing it in the receptacle box, but I think there's a rule against relying on the device itself for continuity of the neutral. You'd need to use a wirenut and a pigtail instead of the pass-thru screws on the receptacle. Especially important if you're putting in a GFCI.

I 'believe' they said it was a 'lost neutral'. Which i didnt really understand back then. But i guess it would make sense. If the power had no neutral line functioning to go back to the transformer.. it has to go some where. Hence over loads, and using the cable line to get back to the tele poll.
Yep, sounds exactly right. Without a neutral service conductor the cable line was functioning (poorly) as a neutral, until it got disconnected and then you had 240V across pairs of circuits. It's a scary situation that happened at my grandma's house, she lost 2 freezers and a bunch of light bulbs, but thankfully it was back before they had a lot of expensive electronics in the house.
 

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Discussion Starter · #18 ·
Back to the original question about the 12/3.
So the set up in the first pic would work; using a empty box to splice the neutrals together and the grounds together.
Would the set up in the 2nd pic work? Just going straight to the first outlet and setting it up like a run; just using a separate hot for the second box?
If both are good; are there any upsides/downsides to one set up over the other?

Almost forgot to add.. each of the two outlet boxes would be a double gang (2 receptacles). So i guess within the box it is a mini run setup anyway... So i would guess that both set ups could work. Tho i dont like guessing in electrical work'
View attachment 694092 View attachment 694093
No problem splicing it in the receptacle box, but I think there's a rule against relying on the device itself for continuity of the neutral. You'd need to use a wirenut and a pigtail instead of the pass-thru screws on the receptacle. Especially important if you're putting in a GFCI.
Yea, both of the double gang boxes would have 1 gfci receptacle and one regular receptacle each. That way the line is protected (basement)

So i guess im thinking something more like this. (forgive poor drawling).
gfci and outlet are pig-tailed together within the box. But the neutral and ground from each box would go be nutted together in a empty box.
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Yea, both of the double gang boxes would have 1 gfci receptacle and one regular receptacle each. That way the line is protected (basement)

So i guess im thinking something more like this. (forgive poor drawling).
gfci and outlet are pig-tailed together within the box. But the neutral and ground from each box would go be nutted together in a empty box.
View attachment 694098
What you've drawn is perfectly fine, but you could do without the middle box if it would be easier. Just wirenut the neutrals in the box behind the first receptacle.
 

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So the set up in the first pic would work; using a empty box to splice the neutrals together and the grounds together.
Would the set up in the 2nd pic work? Just going straight to the first outlet and setting it up like a run; just using a separate hot for the second box?
You do not need a third empty box to do the splitting.

You can run a MWBC from the panel to box A (use red wire there) to box B (use black wire there) to box C (use red wire there) and on and on.

However, you may be aware that in all boxes, you must pigtail grounds, so that if a device is removed, you do not cut the ground. Obvious safety necessity right?

OK, In MWBCs you must also pigtail the neutrals. For the same reason, removing a device must not cut the neutral. (Because if you interrupt neutral on a MWBC, you get a "Lost Neutral" condition on the rest of the circuit).



As far as GFCI protection, with MWBCs you need to use GFCI receptacles at each location where neutral is shared.


As far as AFCI protection, you can't --- hold on. Maybe. Tell us which manufacturer your panel is.
 
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