OldSchool500
Member
I know you can separate the two outlets on a normal dual receptacle. Does this mean I am allowed to use each as a dedicated circuit? For example, 20A top, 20A bottom, shared neutral?
Two circuits on one double receptacle?
- Thread starter OldSchool500
- Start date
Shiftless
Well-known member
Let’s wait for a real electrician to chime in but in the meantime, I’d say that using a duplex receptacle for 2 separate dedicated circuits would be OK. AFAIK.
You’ll break the bridge between the two right?
You’ll break the bridge between the two right?
OP
OldSchool500
Member
Definitely.
Yes you can, but it must be a 20a receptacle and fed from a 2 pole cb, not a tandem cb.
Not the case with a MWBC.
ok it's got to be opposing legs. derp.
wyliesdiesels
Well-known member
75gmck25
Well-known member
Since a MWBC shares a single neutral for two circuits, I assume your plan is also fine. However, I think it would also require the two circuits to be on one double breaker so that power goes off in both circuits at the same time. Otherwise, if you turned off only the circuit for the top receptacle (for example), you could still have current flowing from the bottom receptacle hot back to the neutral.
Cruzan80
Well-known member
Now, if there is only one outlet on the circuit, does that mean he would have to use a 20A outlet (since it is a "single" receptacle at that point for each)?
We may have finally found a home use reason for all of those 20A outlet sales at Home Depot!
We may have finally found a home use reason for all of those 20A outlet sales at Home Depot!
LopezBart
Well-known member
This is likely obvious to everyone, but the advantage of running one's shop outlets circuits this ways is that one can switch out the 120V outlet for a 240V at any point in the circuit, so if that new grinder needs 240V, you can make it works pdq.
To be pedantic, all devices on the same yoke (for a receptacle outlet and the like, that’s the two #6 screws holding it to the box) have to be disconnected simultaneously. A two pole breaker is the simplest way and probably cheapest, but two single pole with a handle tie will work too, and keeps them independently tripping. (This changed in the 2011 code cycle, so there are lots of non-tied mwbc in Chicago, where mwbc are used for the space saving in conduit. My house has 16 or 18 of them, almost every general use circuit is done this way. Many of them split up at the first box, to make best use of the existing conduit to the panel location, and make no sense otherwise. )
Along with converting to 240, mwbc save wire, and they have just two current carrying wires. That is valuable for conduit systems. They also confuse the hell out of Harry Homeowner types, which
Cruzan80
Well-known member
This also helps in a garage if you have major equipment running close to limit of the circuit. The second outlet/circuit allows for a shop-vac or other small accessory tool, when running a 15A+ tool. Mine is set up so the top circuit handles all of the stationary "plug-in" 120 loads, and the bottom is for accessory use.
True, but at 2:36am, that was good enough.
Codyboy
Well-known member
I ran all my shop receptacles like that. Not only can I make it a 240 receptacle but used less wire and had only 1 pull for two circuits.
?? It would always be the same or less amps on the neutral. Could actually be 0 amps on the neutral if both circuits had the same load.
Cruzan80
Well-known member
The above is attempting to clarify both quotes. If I am wrong, please correct me.
Besides the complexity of tying the handle together, wouldn't a single tandem be pulling both 20A circuits from the same leg, therefore not cancelling out along the shared neutral (my understanding is that the opposing legs allow the current to "cancel")? If someone were theoretically to do this (they would be making their lives infinitely more complicated), would the neutral need to be sized for 40A then?
My understanding is is why @mm08822 said not to use a tandem (aka two mini-breakers pulling from the same leg). Using two tandems and tying the inner or outer air together would be fine, as would using two single pole with a handle tie, or a double pole breaker.
Or did I screw up the verbage? I thought tandems were breakers with two handles, that physically fit into one breaker slot.
Edit: Yes, tandems were what I had thought, per the pictures below.
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BillK
Well-known member
Just curious why on earth you would want to do this ?
Cruzan80
Well-known member
If this is in relation my my post on a MWBC on a tandem using the same leg for both, I thought I had pointed out that it was a very bad idea, and was trying to lay out the why.
Single pole cb - One handle, attached to 1 phase, fits in 1 full-size slot
Double pole cb - One tied handle between 2 cbs, attached to "both phases", fits in 2 full-size slots
Tandem cb - Two handles, attached to 1 phase, fits in 1 full-size slot
Quad cb - One or two tied handles between 2 tandem cbs, attached to "both phases", fits in 2 full-size slots
and triplex(which I've been calling quads all along)
(connects like a quad)Attachments
yatg
Well-known member
If you're going to the trouble of running a 12/3 to a new box, make it a 2gang and put a duplex receptacle on each leg.
Codyboy
Well-known member
This is what I was going to post next as a follow up to BillK , well actually the OP.
When I read BillK's reply of why I thought he was / is saying why do it on a single split duplex. Get more bang with a 2 gang and have 4 receptacles.
micromind
Well-known member
Single pole cb - One handle, attached to 1 phase, fits in 1 full-size slot
Double pole cb - One tied handle between 2 cbs, attached to "both phases", fits in 2 full-size slots
I like the 35 and the 10 amp breakers. I've installed a number of both.
As noted, provided that both halves are on different phases, the neutral won't be overloaded.
NightSky
Well-known member
Just looking for clarification on the above statement about switching out a 2 phase divided 120V outlet for a 240V one: on this same MWBC there can be a mix of 240V and 120V receptacles?
Codyboy
Well-known member
Sure why not? As long as you stay within the load application of the circuit. The circuit or breaker don't care one way or another if you're plugging in 120 or 240.
If it's a 20 amp circuit thats the only thing you're bound by.
I have several machines that can run on either. Right now like my bandsaw runs on 120 on a 20a circuit. I could reconfigure it to run on 240 .
Same with my air compressor. It's on 120 now but once I move it to the shop , I'll probably wire it for 240 and use one of my MWBC to do it.
ETA.
One reason I want to do 240 on machines that will do it is load balancing. Nothing more. They run just fine on 120 though.
micromind
Well-known member
Yes there can but the breakers must open both circuits simultaneously. Basically, a 2 pole breaker.
The same applies with 2 circuits feeding one duplex receptacle.
that is exactly how and why my shop is wired.
NightSky
Well-known member
Thanks both for the clarification. I wasn't questioning the concept as much as making sure I was reading the original comment from LopezBart correctly.
Interestingly, if I'm thinking about this correctly, if you have, say, a 10A load from a 240V appliance on the circuit and a 10A load from a 120V appliance elsewhere on the same MWBC, the double pole breaker is at capacity (or one side is). Whereas with only 120V appliances, the circuit could handle 20A through both poles for a total capacity of 40A.
Codyboy
Well-known member
Nm . Tired
Delete
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You don't have 2 phase, 2 phase does exist in certain areas but is extremely obsolete.
Chuckster in NJ
Well-known member
The neutral carries the imbalance.
EG: Phase A is 10 amps and Phase B is 8 amps THEN the neutral will carry 2 amps.
TIP! You can’t use a single GFI BREAKER on a MWBC.
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LopezBart
Well-known member
Of course you can... it just needs to be a double pole GFCI breaker. In this type of GFCI, tripping occurs when the difference between the current in the hot lines is not equal to the current in the neutral line.
And you'll lose both circuits simultaneously!
mike93lx
ALLIANCE MEMBER
Oh the humanity!
Chuckster in NJ
Well-known member
I meant to say SINGLE GFI……… Thanks and I fixed it!
mike93lx
ALLIANCE MEMBER
You can't use a single breaker on a MWBC anyway. What am I missing?
Single pole gfi.......but you can use a single double pole gfci
Chuckster in NJ
Well-known member
It’s early!……. Gimme a break!Single pole gfi.......but you can use a single double pole gfci
Codyboy
Well-known member
Huh?
Load is load. It doesn't matter if its a 20 AMP MWBC or two single 20 amp circuits. The advantage of the MWBC is it can serve 240 or 120 or both.
Your 240v appliance with a FLA of 10 amps,
L1 , 5 amps
L2, 5 amps
N, 0 amps
Your 120v appliance with FLA of 10 amps,
L1, 10 amps
L2, 0 amps
N, 10 amps
In total,
L1, 15 amps
L2, 5 amps
N, 10 amps
Scenario Simplified on load and not allowing for derating of a 20a circuit.
Not sure what you mean 40 amps total if they were 120v 20 amps circuits.
You can still add more load to the total above and have 20 amps per line.
Add +5a to L1 =20 amps
Add +15a to L2= 20 amps
Unless I misunderstood your post.
rlitman
Well-known member
You did. With 240V, 10A FLA, both L1 and L2 will have 10A current. Here's how your table should read (assuming PF=1):
Your 240v appliance with a FLA of 10 amps,
L1 , 10 amps
L2, 10 amps
N, 0 amps
Power = 2400W
Your 120v appliance with FLA of 10 amps,
L1, 10 amps
L2, 0 amps
N, 10 amps
Power = 1200W
Note how the 240V 10A appliance draws twice the power as the 120V 10A appliance.
In total,
L1, 20 amps
L2, 10 amps
N, 10 amps
Power=3600W
With both, L1 is at it's limit (not accounting for derating).
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