Electrical code question

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After running two separate circuits for my daughter's dishwasher and waste disposal, I was told that I could have simply run a three wire cable (still 2 breakers) from the panel box and fed the appliances separately. I understand the concept, but, there would be 2 hot wires and only one neutral. Would not that neutral carry twice the current it is designed for? Thanks for explanations and comments. Ivan Vegvary
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It depends. This is commonly known as an "edison circuit". If each of the two breakers were on different legs of the 240v service, then the current in the grounded conductor will cancel out, such that if full load is drawn on both of the two hot conductors, the current flow in the grounded conductor (aka neutral) will sum to zero.
If they're on the same leg, then yes, you'll draw 2x the current on the grounded conductor, which would be a code violation.
Using a commercial handle-tie 240v breaker is recommended, as it will ensure:
a) That the two circuits are on opposite legs b) That both circuits must be disconnected simultaneously.
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On Thursday, May 21, 2015 at 11:01:20 AM UTC-4, Scott Lurndal wrote:
To add to that, if you have two 20 amp circuits on opposite legs, the current in the neutral will always be between 0 and 20 amps. Only the unbalanced portion, ie the difference between the two flows in the neutral. For example, 15 amps on one, 5 amps on the other, you have 10 amps in the neutral.
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On Thu, 21 May 2015 15:01:15 GMT, snipped-for-privacy@slp53.sl.home (Scott Lurndal) wrote:

It is NOT recommended. It is required by code. It is mandatory. Doing it any other way is total stupidity
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On Thursday, May 21, 2015 at 10:42:48 AM UTC-4, Ivan Vegvary wrote:

you really did this the best way. makes future troubleshhoting easier, and its a one time expense, so a little extra now doesnt matter.
plus witheach item on its own breaker service is easier.
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waste disposal, I was told that I could have simply run a three wire cable (still 2 breakers) from the panel box and fed the appliances separately.

neutral.

its a one time expense, so a little extra now doesnt matter.

+1 Saving the cost of a single wire and an extra breaker isn't worth the problems that can arise from using Edison circuits. He's dead. They should be, too. (-:
--
Bobby G.



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On Thu, 21 May 2015 20:58:14 -0400, "Robert Green"

Up here they are called "split" circuits, particularly when feeding a single duplex outlet..
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On Thu, 21 May 2015 21:55:24 -0400, snipped-for-privacy@snyder.on.ca wrote:

The NEC name is "Multiwire circuit"
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On Thu, 21 May 2015 20:58:14 -0400, "Robert Green"

What "problems"? There are certainly advantages beyond saving 2 wires per circuit. Not the least of which is voltage drop mitigation. (up to 50%). You also get to use smaller/fewer boxes. It is only a problem for people who do not understand what they are looking at and they shouldn't be fooling with them in the first place.
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On 05/23/2015 06:39 AM, snipped-for-privacy@aol.com wrote:

Statistically, multiwire/Edison circuits don't have a bad track record but I still wouldn't have one in my home. Not worth the risk.
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On Saturday, May 23, 2015 at 9:08:10 AM UTC-4, Mayhem wrote:

The risk of what exactly?
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On 5/23/2015 9:19 AM, trader_4 wrote:

Suppose you have a heavy resistive load on leg 1 and a light load on leg 2 and then suddenly lose the neutral. What happens to the voltage across the light load on leg 2? Would 230 volts smoke a small radio on leg 2?
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wrote:

That is what happens when the power company's neutral feeding the house goes haywire.
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On Saturday, May 23, 2015 at 11:49:50 AM UTC-4, Bill wrote:

That's a valid point. If it happens, you could wind up with up to ~240V on the unfortunate load side, something that can't happen if it's a regular circuit.
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<stuff snipped>

Magic smoke will be forced out of the small radio perhaps even a loud magic noise, too. (-:
While a reputable electrician would probably not make this particular mistake, it's possible for a future modification or rearrangement of breakers in the panel to inadvertently move one or both individual breakers (especially in older work) so that they both end up on the same 120V leg of the panel - which is improper when a shared neutral is involved. If the split circuit is installed that way, the shared unbalanced load could exceed the rating of the wire.
Maybe some NEC expert can tell us when the use of a double-pole breaker became a code requirement for Edison circuits because I know it wasn't always that way (or that way in 1988). My kitchen had an Edison circuit *without* a tied breaker until I rewired it with separate runs. Without the tied breakers or a double pole breaker that kills power to both phases, it is quite possible for someone to be shocked while working on the circuit, since the neutral wire of the supposedly "dead" circuit could be carrying current from the sister "live" circuit. DAMHIKT. (-:
There's so little benefit, IMHO, that the risk of using Edison circuits today doesn't seem worth it. If voltage drop is a problem, use a larger diameter wire. If you can't afford the extra wire, check the car's seat cushions for spare change or sell some blood. (-:
Besides, the last time we had this discussion I believe I pointed out that because "Romex" 12/2 w/G and 14/2 w/G is so widely used, it can often be had on sale for much less than 12/3 or 14/3 w/G, thus totally negating any real savings in wire costs.
Same problem with the 2 pole GFCIs needed to protect an Edison circuit. I can always find a good sale price on the single circuit GFCIs. I don't recall ever seeing a double pole unit on sale. I do recall when I looked at 2P GFCIs they cost way more than 2 separate 1P GFCIs. I recall paying a little more than $10 a pop for 20A Leviton GFCIs just a while back when I ran a new sump pump circuit.
http://www.google.com/search?q=cost+dual+pole+GFCI
The 2P units Google shows are in the $80-$110 range. So it looks like the Edison circuit is going to end up costing way more than two comparable single branches, at least if you don't pay list price for your components.
I don't see the tradeoffs being worth it but obviously some people do. For me it violates the KISS rule.
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On Sat, 23 May 2015 17:53:06 -0400, "Robert Green"

I believe it was a code requirement long before 1988, at least in Ontario. My 1974 house, with a fuse panel, has ganged fuse pullouts for all the split circuits, and they were a requirement back when I helped my electrician father wiring houses as far back as 1965 or 1966.
Canadian code is often much more strict than american code when it comes to safety - so what it was in the US of A is anyone's guess.

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<stuff snipped in line>

I don't live in Canada. Best I can find is that it became part of the code in 2008, but that's certainly not definitive - just came across a few discussions that seem to indicate that's when the NEC required the tie handle or dual pole breakers.

In Canada, perhaps, but I don't think that was the rule in the US based on the reading I've done. Perhaps an American NEC expert has the answer. I know we used to have some NEC-heads here once upon a time.

Well, I suspect it's not a guess, but a very clearly documented fact that we just don't have yet and since I cleared my browser history, I can't even provide the cites that implied it was a relatively new code requirement in the US. I believe it became mandatory in 2008, but that's a guess - it wasn't what I was paying attention to.
The bottom line for me is WHY would anyone use an Edison circuit and a *very* costly two pole GFCI (compared to two single pole) when they could get by easily with two discrete circuits? It also seems counter-intuitive to plug two power-hungry devices into the same outlet which is what gets done with a split-wire receptacle.
Maybe you save some bucks by not having to rough in a second outlet but my personal rule of thumb is that you can't have enough outlets in today's modern kitchen. Using a split-wire receptacle seems to reduce rather than increase the total outlet count. Then, someone might use one of those one-to-six outlet adapters which, depending on how they are wired, will burn up when plugged in because it combines the hots of both sides of the split-wire receptacle. I'm sorry, but just because Canada does it that way doesn't mean it's superior in any way. From what I can determine, it's NOT safer and it's not cheaper. So why bother?
If you list out the pros and cons, the biggest con turns out to be the high cost of a two pole GFCI protector. That cost totally negates any potential saving in wiring $ except in huge houses. The fact that 12/3 and 14/3 is far more difficult to find on sale also tends to negate the cost saving.
In addition, running two high amperage devices like skillets and toasters out of one outlet box would, IMHO, tend to increase the chances of overheating something in that box. It could be anything from a bad backstab to an improperly inserted plug. And if that neutral back stab fails for any reason, you've got the potential magic smoke problem again.
There's also the question of whether bringing 240 volts into a wet kitchen area into one single box is a good idea to begin with. Anything that goes wrong becomes a potentially much more lethal 240 volt event.
So what makes an Edison circuit so great that they are mandated in Canada, eh? (-: I still don't see it. A second outlet run to the kitchen would probably cost less, in materials at least, than wiring up an Edison circuit. That second, standard 20A circuit would also be much more likely to survive a repair attempt by a homeowner than an Edison-type circuit.
I seem to recall someone here in the past had trouble distinguishing a switched outlet from an Edison circuit, yet another reason to avoid them.
I believe the only reason I had an Edison circuit here is that the house was built in the year of the steel penny when copper was in such short supply the US Mint stopped using it to make pennies that year.
When WWIII comes and copper becomes incredibly precious *again* I'll consider wiring with Edison circuits, but until then I'm happy with my on-sale $10USD GFCIs, my 250 ft coils of 12/2 w/g (blue, by the way, in case anyone from the color coding of NM wire thread is reading) and my extra *metal* junction and outlet boxes. KISS unless you live in the Great White North, I guess. (-:
--
Bobby G.



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On Sunday, May 24, 2015 at 7:15:51 AM UTC-4, Robert Green wrote: wasn't what I was paying attention to.

Another factor is if you go the peculiar split receptacle approach that Clare says they use up north, you can forget about having the GFCI at the receptacle, where it's easy to reset/test. I've never seen a receptacle with built-in GFCI that's double pole. So, you'd need a double pole one at the panel. I'd rather have it near where the receptacle is.
I don't get the whole idea behind splitting a receptacle and putting each half on different legs. Here I see it done sometimes to put one half on a switch, the other on all the time, on the *same* circuit. That makes sense. Say what you want about Edison circuits, but this Canadian thing, I don't understand what the purpose is all about. And also, if you want to start in about potentially having two different circuits in a box live, it's funny that Edison gets dragged in as the solution. It would seem to me the finger should be pointed at whoever up in Canada required their screwy split outlets.

For the most part, it's not going to create a more lethal environment. If it gets wet, energizes some metal, etc, you still only wind up with 120V to ground. To get 240V, you'd have to somehow wind up across both legs, and that kind of fault would be extremely rare.
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On Sun, 24 May 2015 05:54:04 -0700 (PDT), trader_4

I was never really sure why they wanted them on the same duplex anyway. If you really need both 20 a circuits in one box, why not use a 1900 box and put in 2 duplex outlets? You usually run out of sockets long before you run out of amps. I ended up with three 2 gang boxes serving the countertop along with a few singles.

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On Sun, 24 May 2015 12:12:02 -0400, snipped-for-privacy@aol.com wrote:

This was code in Canada before 20 amp circuits became code.

+1
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