We are in the process of wiring a house we are working one.
One of the guys asked if you run a 12-3 wire to power 2 outlets for say, a washer and a dryer (gas) and both are running at once, is not the single neutral carrying twice the current?
The only answer I could come up with is that the two circuits will be 180 degrees out of polarity so the currents don’t add up.
It has been over 20 years since collitch physics!
Did I get it right?
This is what I loved about my engineering education, 5 years of mundane science and math, interspersed with random bits of useful knowledge!
Mr T
Do not try this at home!
I am an Experienced Professional!
Replies
Did I get it right?
Close enough, so long as the two hots are on opposite legs of the power supply.
_______________________
Worship is not an hour in a building; even in a building dedicated to God.
Worship is an encounter with the holy presence of God!
I'll add a tad to Bob's answer.
So long as each hot side is connected to an opposite leg, the neutral will only carry the difference of the ampacity. If the dryer pulls 8 and the washer 12........the neutral would carry 4.
That's right. The two hots also need to be on a dual breaker with a common trip.
The two hots also need to be on a dual breaker with a common trip.
Are you sure about that? That isn't the practice in my area for 2 110 circuits with a common neutral; only for 220 circuits.
_______________________
Worship is not an hour in a building; even in a building dedicated to God.
Worship is an encounter with the holy presence of God!
That was my understanding as well. You use 220 and get two 110 circuits.
"That's right. The two hots also need to be on a dual breaker with a common trip"
No, while that might be a wise thing to do, it is not required.
A common trip 240 breaker is only required when you have 240 volts on a common yoke.
Article 210-4(b) states that "In dwelling units, a multiwire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated." I've always taken that to mean that approved handle ties are acceptable, which would cause both poles to disconnect when either one is flipped. It doesn't mean that when one trips it has to carry the other with it, though.
This is alluded to in 210-4(c) Line to Neutral Load., "Multiwire branch circuits shall supply only line to neutral loads.", but with exception No. 2, "Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch circuit overcurrent device.", which means a 2-pole breaker just like any other 240V load. A typical electric clothes dryer would fit this description, as well as those 120V/240V combo receptacles you can buy in the big boxes.
When a multiwire branch circuit does not supply 2 devices on the same yoke, there is no requirement to tie the handles, or use a 2-pole breaker; just to pigtail the neutrals.Be seeing you...
That must be from the 99 (which I have) or older.
I believe that they rewrote that mess for the 2002 NEC so it really puts those into one section and basically it is what I wrote - if you don't have 240 on a yoke (which it is 120 device that is split to the two legs or a 24o volt device) then you ganged breaker.
That language is the same in both my '96 and '02 books. The intent, as I understand it, is that you want handle ties at minimum (2-pole breaker does the same thing, of course) on a multiwire circuit powering a 2-circuit yoke so that if you shut down one, you have to shut down the other. Otherwise, you could grab a handful of 120V thinking both the devices are dead (I guess most people are not likely to check both), when one is still live. But 2 yokes in the same box can be on separate circuits, including a multiwire, and not need the handles tied, since you're less likely to get zapped (2 circuits in one box are common). Once they've left the junction point, they are separate circuits, anyway. Of course, you could still open the neutral where they're pigtailed with one of the circuits live and get jolted, so I'm not necessarily disagreeing with having handle ties even when they're not specifically required, but there is the burden of shutting down the other circuit every time, even when it's not necessary. But there is no requirement that one CB tripping out on overload take the other one with it, unless at least one of the devices has 2 ungrounded conductors (240V), requiring common-trip just like always.Be seeing you...
Thanks for all the great answers!
Now on the double breaker/handle/split 220 thingy.
My 3 cents
When not in use a neutral has no voltage and thus carries no current.
But when said circuit is being used (to run the dishwasher) then the neutral is carrying current and has voltage.
If you disconnect one side of a split outlet(the disposal) and the dishwasher is running, the neutral is effectively a "HOT" wire!
Methinks it wouldst be best if one were to disconnect the "other" side of a split circuit before working on the "other-other" side!
The code recognizes this as a rare but potentially deadly circumstance.
Actually it is probably not common than one would think.
And since seasoned electrician are not the only ones who will ever work on electrical circuits, it is always better to make them as idiot-proof as possible.
Maybe that was worth 4 cents!!??
Maybe not!
Mr T
Do not try this at home!
I am an Experienced Professional!
No, while that might be a wise thing to do, it is not required.
A common trip 240 breaker is only required when you have 240 volts on a common yoke.
Sorry, my faulty memory. I was remembering a NEMA L14-20 receptacle I recently put in my shop (ceiing mount, with the idea it could be used to either power a 240V tool, or to provide 2 120V circuits). I followed 210-4(c) Exception#2 and used the dual breaker. But in the 210-4(b) case only the handle tie is needed (I think as you said, the dual is still a good idea).
Someone mentioned doing this in a kitchen; in that case I think you'd need a dual breaker, a 240V GFCI breaker, since kitchen branches need to be GFCI?
"Someone mentioned doing this in a kitchen; in that case I think you'd need a dual breaker, a 240V GFCI breaker, since kitchen branches need to be GFCI?"
Yes, depends on how they are wired. If I was doing that I would wire every other one to one leg and could use individual GFCI's, but after a few the price might be equal.
Now, from what I have seen here, in some parts of Canada they they split the duplex recpetacles. In that case the 240 breaker GFCI is the only way to go.
You are correct in describing how to do the work. In the United States, though, kitchen outlets must be 20 amp, so 12 gauge wire would be required. Split outlets are not common here.
Actually, one side of the circuit can trip by itself. The reason for tied breakers is to:
a) ensure that anyone working on the circuit has to shut down both "hots"
b) because of box design, the tied breaker ensures that opposing legs across the 220 are used
As a sidebar, most of us have a bridge in our toolbox so that we can pull 220 from a kitchen outlet.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
phill
can you explain the "bridge" for using 220 from a kitchen split?
what would you use it for?
stevecaulking is not a piece of trim
2 110v male plugs, the hot side of each wired to a female 220v recepticle. 1 ground is wired to the recepticle.
Used to power 220v equipment.
SamT
With thanks to Sam for explaining that. Yes, in the GTA (and probably a lot of other places), every kitchen counter recepticle is split. Further, each one is on it's own 220 three-wire circuit and unique breaker (mine are even on 12-guage, but I can't remember off-hand if that's a reg, or we just did that). I've been told that there's hard statistical evidence that this has significantly reduced the incidence of kitchen electrical fires in homes built after this regulation came in. Many kitchen appliances have really heavy draws and upping the ampacity wasn't our solution (there are NO 20 amp circuits in normal homes here - devices are certified to run safely on 15 amps).
And this can be used in many ways, 220V equipment includes: renting ventalation fans for painting, portable 220V heater, welder, some of those big electric tools (like breakers, large drills, etc.), a bigger compressor to run that big air-tool, ...
Phill Giles
The Unionville Woodwright
Unionville, Ontario
With apologies, I'm gonna detour the thread slightly with a question for my American cousins...
In Canada, as noted, we have split receptacles over kitchen countertops. Each box is wired with 14/3 and a double 15A breaker.
This year, they changed the code to allow for (I think) a U.S.-style wiring method: running 12/2 20A to a kitchen countertop box and not splitting the receptacle. This is an alternative to the older method, not a replacement.
However, in addition to this change, they mandated the kitchen breakers must now be GFCI. Holy crap! I thought $70 was a bit rich for an arc-fault breaker, but a double 15A box GFCI is $240!!! That's 10 times the price of a regular breaker! Heck, you can buy the entire panel for that kind of money.
Is pricing the same in the U.S.?
Regards,
Tim Ruttan
I haven't priced the the 15/20 amp ones, but you can get the 60 amp GFCI breakers for about $60 used for hot tubs.
I suspect that someone look at a manufactures price list. I know that SQ D has list prices like that. I saw a simple disconnect swtich/box for AC's that list at something like $70, but was readily availbe for $10-13.
The US standard is for a MINIUM of TWO 20 amp circuits for the counter tops. Typically the outlets are not split, but alternated between the two circuits.
Also any countertop 12" or bigger requies an outlet and one is needed every 4 ft.
So it can you can end up with a fair number. If each box required separate 14/3 and 240 breaker even an average kitchen would require a sub-pannel.
But most of that would be wasted. You don't need dedicated circuits for mixers, can openers, coffee mills, radio, etc, etc.
Our rules allow for single-purpose regular duplex outlets (e.g. fridge, microwave, convection oven, etc.).
Phill Giles
The Unionville Woodwright
Unionville, Ontario
"Our rules allow for single-purpose regular duplex outlets (e.g. fridge, microwave, convection oven, etc.)"
Ours also. I was just talking about the MINIMUM for GP coutertop outlets.
this is just for my area that I know of,local regulation.
The split circuit with 12/3 is illegal on kictern counter circuit, in my district. Also gfi do not like 12/3 circuits. Here each plug must be a gfi not the circuit breaker.
But I only know this because I got wrote up on it. that and wrong color wire nutts
Steve, BrownBagg, Bill & Phill:
as I mentioned, Canadian code this year was updated to allow a U.S.-style kitchen wiring (20A 12/2), but retains the old style split receptacles (15A 14/3) rules, as well. GFCI at the panel for kitchen plugs (new rule) is a must regardless of wiring methodology.
Steve, there are few high-draw countertop appliances (especially with more microwaves having dedicated circuits installed), but most aren't (or aren't on simultaneously), so the 12/2 arrangement works fine. Even if you draw more than 20 amps on the circuit, chances are the overload won't be big enough/long enough to trip the breaker. Or you learn to plug the toaster and coffee maker into different circuits. 20 amp breakers with 12/2 wire is a cheaper way to wire a shop than split receptacles, and you probably won't have a problem with a 15A saw and an 8A shop vac on simultaneously. Heck, I've run them both on 15A circuits.
I haven't got a copy of the code in front of me, but I think that the 12/2 method will allow for one fewer GFCI breaker to be used, as two boxes can be on one breaker as long as the boxes aren't adjacent to each other. I've mentioned the outrageous price for these breakers, so if my understanding is correct, look for the 12/2 method to become the new kitchen standard in Ontario. However, the 14/3 rules might have been modified to allow non-adjacent splits to be on the same breaker, too...not sure.
Bill, typical Ontario kitchen wiring is 3 split receptacles, all 15A 14/3 wired. 6 breakers, plus a dedicated circuit for the fridge isn't a subpanel. Countertop outlets can be no more than 6' apart, meaning anywhere on a counter has to be within 3' of an outlet. And thanks for the price info.
BrownBagg, not sure why a 12/3 split would be non-code or even a 14/3 split, but you Yanks do lots of things I don't understand. ;-) The fact that your kitchen plug has to be GFCI and not the breaker really baffles me, however; our rule is specifically the opposite (except in bathrooms). And wrong colour wire nuts? Huh? Sometimes a colour represents the size of the nut (and therefore capacity), but otherwise we can use orange, yellow, red, black, blue, turquoise with pink polka dots, etc. Or were you referring to a capacity problem? If so, you naughty, naughty person! ;-)
Regards,
Tim Ruttan
"Steve, there are few high-draw countertop appliances (especially with more microwaves having dedicated circuits installed), but most aren't (or aren't on simultaneously), so the 12/2 arrangement works fine. Even if you draw more than 20 amps on the circuit, chances are the overload won't be big enough/long enough to trip the breaker"
That is so ture.
My house was built in 79 so it does not all all of the dedicated circuits that are notw used. I have just the two 20 amp circuits not only for the counter top, but also for the refigerator, dishwasher, traash compactor, garbage disposal, and instant hot water dispenser.
And I just have a counter top microwave so it plugged into one of the counter top outlets.
"BrownBagg, not sure why a 12/3 split would be non-code or even a 14/3 split, but you Yanks do lots of things I don't understand. ;-)"
Well the 14-3 would not meet code, because 20 amp circuits are required in the kitchen. The 12-3 circuit does meet code by the NEC. But there are local modifications and probably more common are local inspectors that don't really understand the code so come up with there own "strange requirements."
The local code not the NEC.
All house wire must be 12 g no 14g
Kicten circuit must be 12/2
12/3 is only allow on a three way switch light circuit (hall way)
all ground wire nuts must be green.
All wire must be copper
wire must be grounded to wire line ( what about PVC)
Only one ground rod allowed ( I got three shhhhhhhh.....)
mirowave only circuit
only one plug in laundry room
But remember this is local, and remember me and inspectors don,t play well together.
Only one ground rod allowed ( I got three shhhhhhhh.....)
?????? Where, exactly, is this?
we got a bad lightin problem so I wanted my a/c unit and satallite dish with a good ground. NEC says you can have as many as you want as long as there are hook together Butif you soil has a resistance it need two rod five feet apart But my inspector is not that smart