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.
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.
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.
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.
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?
Magic smoke will be forced out of the small radio perhaps even a loud magic
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.
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.
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
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.
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. (-:
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.
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
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