No truer words were ever spoken. It seems to me that the MWC *reduces* the
available outlet count and encourages people to use "cheaters" like six-way
plug-in adapters to get more outlets. They can be pretty dangerous if the
hots are connected in the adapter. I've used some. The older ones did tie
the neutrals together but the newer ones don't. The cheapest of them had
press-fit connectors between the outlets and the internal bus bar of the
adapter. When one of the connections came loose, it arced and melted the
On Sun, 24 May 2015 06:59:58 -0400, "Robert Green"
It makes it virtually impossible to overload a circuit when each half
of a duplex receptacle is on a separate circuit. You can plug a
toaster and a coffemaker into one "outlet" with no danger of
overloading it - and only have one wire required to be pulled for each
"outlet" - giving you, in effect, a 30 amp circuit.
What I have seen done for dual GFCI (And even single gfci) protection
is to run from the panel to a box with a gfci outlet, and feed-through
from there to the house circuit. The GFCI protector is on the panel
board with the electrical service panel, but is not IN the panel (for
cases where a gfci or dual gfci is either not available or
Disagree. Teaching people to plug high amperage appliances into the SAME
outlet is just wrong. They'll tend to generalize and think EVERY outlet can
handle 30 or 40A loads. What does your average Joe Homeowner know about
Edison circuits? Nada, zip, bupkiss.
Because it's SO simple to add an extra box and circuit when you're doing the
work, it seems like very false economy to save a little money (maybe -
you've read my comments on wire costs and sales) and create an outlet that
encourages people to overload *all* outlets because "the one in the kitchen
never blows a breaker." Joe Homeowner is hardly likely to know that just
those outlets in the kitchen can handle multiple high-amp loads plugged into
If running large loads out of one duplex outlet is the main reason for using
Edison circuits (and it's a weak one IMHO) I counter by saying you can do
exactly the same thing with a discrete feed from two breakers at the panel
with no shared neutral. Same effect.
Then you can pull 40A from one duplex outlet if that's what floats your
boat. Doing it with two discrete circuits and no shared neutral means you
can use single pole (and MUCH cheaper) GFCIs using the downstream options or
GFCI breakers in the circuit panel.
I'm still not convinced Edison circuits are saving anyone any money or makes
them safer in any way. Mostly what I've heard is "gee, you can run one less
conductor" as if that's really a substantial savings in wiring or labor
costs. It's not if you're going to run a new cable anyway.
Explain to me again how you can GFCI protect an Edison circuit with two one
pole GFCIs? The current in a shared neutral fluctuates with the load on
both phases. Only a dual pole GFCI can monitor both hots simultaneously as
I understand it. From what I've read at least some people who have tried to
install two single pole GFCIs on an Edison circuit have been plagued by
nuisance trips. Others have had success, apparently, by separating the
shared neutral into two discrete wires before connection to the GFCIs. But
that's no longer a true Edison circuit.
There may be a proper way to do it, but it seems inordinately "klugy" to try
to force two single pole GFCIs to do something they weren't designed to do.
It seems a long way to go for very little reward. Just run two circuits
instead of an Edison circuit and you can use the much cheaper single pole
GFCIs and you can use them in the pass-through mode to protect all
I'm not the only one who isn't sanguine about MWCs:
Destruction of Equipment. Never remove the grounded (neutral) conductor from
the grounded terminal bar in the panelboard if the phase conductors are
energized. The grounded (neutral) conductor you remove could be part of a
multiwire branch circuit, so this could result in destruction of electrical
equipment. More important, even if the return conductor is not part of a
multiwire circuit, removing a conductor from the grounded terminal bar when
the circuit is energized could result in injury due to shock or arcing.
A typical 3-wire circuit is actually two otherwise-separate parallel
circuits with a common conductor. If the grounded (neutral) conductor is
accidentally opened, the circuit changes from two separate parallel 120 V
circuits to one 240 V series circuit. This can result in fires and the total
destruction of electrical equipment.
For example: A single-phase, 3-wire, 120/240 V circuit supplies a 1,275 W,
120 V hair dryer and a 600 W, 120V television. If the grounded (neutral)
conductor is interrupted, it will cause the 120 V television to operate at
163 V and consume 1,110 W of power (instead of 600 W) for only a few seconds
before it burns up. Figure
Step 1. Determine the resistance of each appliance, R = E2/P.
a.. Hair dryer rated 1275 watts at 120 volts.
b.. R = E2/P, R = 1202/1275 = 11.3 ohms
c.. Television rated 600 watts at 120 volts.
d.. R = E2/P, R = 1202/600 = 24 ohms
Step 2. Determine the circuit resistance: RT = R1 + R2
a.. RT = 11.3 ohms + 24 ohms = RT = 35.3 ohms
Step 3. Determine the current of the circuit: IT = ES/RT
a.. IT = 240 V/35.3 ohms = 6.8 A
Step 4. Determine the voltage for each appliance: E = IT x Rx
a.. Hair dryer: 6.8 A x 11.3 ohms = 76.84 volts
b.. Television: 6.8 A x 24 ohms = 163.2 volts
The 120 V rated TV in the split second before it burns up or explodes is
operating at 163.2 volts.
Step 5. Determine the power consumed by each appliance: P = E2/R
a.. Hair Dryer: P = 76.82/11.3 = 522 watts
b.. Television: P = 163.22/24 = 1100 watts
The 600 W, 120 V rated TV will operate at 163 volts and consume 1110 watts.
You can kiss this TV goodbye!
All to save (perhaps) a few bucks on cable costs. Not worth it.
On Sunday, May 24, 2015 at 5:13:54 PM UTC-4, Robert Green wrote:
It's one less conductor, but two less wires, the other being the ground.
Your point on increased cost of double pole GFCI breakers versus
two single pole probably negating some or all of the cost savings is
valid though. But that's only if you put the GFCI at the panel.
You could use two GFCI receptacles at the end of the Edison circuit.
Good catch. If you do it as Clare suggested, it won't work. He's
claiming you can put a GFCI outlet or outlets next to the panel and
feed the Edison circuit from that. It won't work for the reasons you
cite. It needs a single GFCI that can sum up the currents on the two
hot legs and neutral and make sure it equals zero. Besides that, it
just gets screwier. Now because of this curious Canadian penchant
for split outlets with Edison circuits, you're supposed to mount more
crap next to the panel too?
I disagree with your last sentence though. You could run an Edison
circuit to where the receptacles are going, separate it into two
runs serving two groups of receptacles. Put a GFCI receptacle on the
first spot on each chain, then feed the others downstream. That will
work and it's still an Edison circuit.
Per the above, an Edison circuit can be used with two GFCIs just
like running two separate circuits and putting the two GFCIs
where the Edison splits to serve two chains of receptacles.
Exact same thing exists with ovens, dryers, spas, any other 240V appliance
that has 120V as part of it. You shouldn't be removing neutrals on
any energized circuit, unless you know what you're doing.
It is an additional potential failure point where bad things could
happen. That already exists with ovens, etc, but I think it's less
likely that a neutral will come loose on ovens, etc than on a circuit
that has a bunch of receptacles, daisy chained.
Here's what I found:
National Electrical Code Citations for Multi Wire and Split Wire Devices
1.. The 2008 National Electrical Code, 210.4(B) Multiwire Branch Circuits,
now requires that effective 1 January 2008,information about conductors of
multiwire branch circuits originating from the same panelboard or
distribution equipment has been relocated to 210.4(A). Now 210.4(B)
addresses disconnecting means for simultaneously disconnecting all
ungrounded conductors of all multiwire branch circuits. Simultaneously
disconnecting all conductors of multiwire branch circuits is now expanded to
all multiwire branch circuits, not just those that supply more than one
device mounted on the same yoke or mounting strap. -- Minnesota Electrical
2.. NEC Paragraph 210-4 addresses multiwire branch circuits.
3.. NEC 210-4-b makes clear that split receptacles must be protected by a
simultaneous disconnect to all ungrounded (hot) conductors (i.e. use a
double-pole breaker with a common trip tie installed). NEC Paragraph 210-4
addresses multiwire branch circuits.
4.. Split-receptacle means each half of a duplex receptacle is wired to a
different "polarity" or phase and the single grounded conductor (neutral) is
used). NEC Paragraph 210-4 addresses multiwire branch circuits.
On Mon, 25 May 2015 22:24:50 -0400, "Robert Green"
Nothing particularly onerous in any of that and those changes have
eliminated virtually all of the issues are hung up on.
You can argue about whether two 12-2 wg is cheaper than one 12-3 and
whether the boxes need to be upsized but the improved voltage drop
efficiency is undeniable and goes on forever.
I2R =$ and a few bucks on the front end disappears pretty quickly in
the out years. If you are at the other end of the house from the
panel, a multiwire circuit starts looking pretty attractive, assuming
you are not putting a sub panel down there ... essentially a big
I suspect you meant to say "you are hung up on." Even so, I am not "hung
up" on anything. The most popular reason I've seen given for using MWC
is that it saves money on wire. But when investigated real-world costs,
that turns out to be untrue. With the recent code changes requiring GFCI
breakers, the economy reason no longer exists. It's more expensive to wire
a MWC because of the extremely high cost of the now required double pole
breaker compared to two single pole units.
You still sound hesitant to admit that's a fact. Is the cost issue in
dispute or do you concede that 2P GFCI breakers are WAY more expensive.
Five to ten times by my estimate. The "saving money by using less wire"
reasoning is now extinct except for fairly unusual circumstances.
Have you found prices that actually make it a reasonable argument because I
have not, especially when you look at sale prices. Whatever you save by
using the more difficult to work with (thicker and stiffer) 12/3 is eaten up
by the special 2P breaker required.
Now I will also agree you can use discrete GFCIs in a MWC if you're into
cluster-fu& engineering, but the proper way to protect MWCs is with devices
in the panel especially designed for the task.
And in how many installations is voltage drop a serious enough problem to
warrant using MWCs? Huge, million dollar houses where the cost of some
extra wire is chump change, I'd venture. In my case, the only device that
would have any problems with voltage drop is the CAC - and it IS normally
wired with MWC's primarily because 240 volts are needed to run the
compressor, not because some Canadian code-meister thinks it's a good idea
to deliver 30 or 40A to a single 110V outlet.
A subpanel is the *right* way to deal with super-long wiring runs. Running
multiple Edison circuits not so much. Besides, homeowner electricians
usually don't go futzing around in sub-panels but they will pull an outlet
in a heartbeat. And most of them won't know jack about why there's 240V
coming into a 110V outlet box. That danger is reduced by the new code, but
How many times have we seen problems like low voltage being an issue in
normal residential work? Far less than we've seen complaints about
backstabs coming loose or wires under connection screws breaking because
they were nicked when stripped, IMHO. Those conditions create the potential
for a broken neutral which is a far, far worse thing in a MWC than it is in
a normal two-wire one.
In my reading I've learned that there are people lobbying the NEC folks to
outlaw MWCs in residential work. Apparently this is a "Apple or IBM" issue
for many people. My major concern is that it's no longer cheaper because of
protection device costs although it's still "sold" that way. I agree with
you that anyone with a voltage drop issue can benefit from a MWC but then
again, they can also benefit by using bigger gauge wire.
That said, I doubt voltage drop in kitchens is a big issue. Those are
resistive loads that are thermostatically controlled. Unlike some motors
that could burn out at too low a voltage, the electric skillet and toaster
can probably tolerate a respectable voltage drop without serious issue. So
I wonder, like you seem to, why the F they're required in Canadian
*kitchens*? The case could be made that it will result in substantially
fewer breaker trips, but so would multiple outlets on normal circuits.
On Tuesday, May 26, 2015 at 5:29:31 PM UTC-4, Robert Green wrote:
What exactly is a cluster F*** about using a regular double pole breaker
in the panel and then two GFCIs on the first two receptacles that need
GFCI protection? From there you can feed downstream outlets just like
with any other GFCIs. Just because you don't understand it, doesn't make
it a CF.
On Tue, 26 May 2015 17:07:08 -0400, "Robert Green"
Why would I need a 2 pole GFCI breaker when I can use 2 GFCI devices
at the far end? They have also loosened the rules on AFCIs and allow
the device type under some circumstances.
I expect the restrictions to be completely gone in 2017.
You are still ignoring the voltage drop issue and in a world with ever
increasing energy costs, it may be a bigger issue than wire. Even so a
roll of 12-3 is less than twice the cost of 12-2, particularly at a
real electrical supply house that does not have promotional prices on
I just looked at HD and 12-2 is $68, 12-3 is $117. The difference will
be less at a real supply house
I also pointed out you only need a 2 pole standard breaker (or a
handle tie kit). The GFCI can be at the far end.
Why? Most people think it is better to have the GFCI near the load so
you can more easily identify and reset it.
Perhaps you should put the numbers in a V/D calculator, even at a
modest 50-60 feet and plot it out over 50 years (the typical design
number for electrical installations)
The NEC is not an instructional manual for unqualified people. If the
concept of a MWC baffles harry homeowner, he should leave the covers
CMP 2 and CMP 5 will laugh that out of the building. NFPA does not
cater to the unqualified. The new emphasis seems to be more toward
energy conservation than making the world safe for DIY guys.
In fact I am not sure I have ever seen that even get to the proposal
The voltage drop issue is I2R losses.
If you are out at 60 feet, not that far, even in a pretty small house,
with 2 circuits pulling 10a each, the combined voltage drop in the
neutrals is 2.3v. In a MWC that is zero. That is 23 watts wasted. (>1%
of the power used)
There are even people promoting going up a size on all branch circuits
to save energy and they come up with the same kind of calculations.
How is that different than loosing the line neutral (which,
statistically is much more likely) Then EVERY circuit in the panel
will have extra high voltage on the lower load side, and low voltage
on the heavily loaded side/
On Saturday, May 23, 2015 at 7:04:47 PM UTC-4, firstname.lastname@example.org wrote:
I guess the argument can be made that the less points of
potential failure like that, the better. And if it's the
service netural that goes open, it's probably less
likely that you'd have a
big imbalance because for a whole house, there would be many
loads on each leg, tending to average things out.
So, I think the possibility that you'd
see close to 240V appear on one leg would be a lot less.
On 05/23/2015 07:04 PM, email@example.com wrote:
Losing the neutral in *my* entrance panel is extremely unlikely. I actually check my panel and meter pan connection every 5 years. Of course the poco neutral is tagged to ground
at my panel as well.
> Then EVERY circuit in the panel
I have lost the power company's neutral TWICE in the past year and a half.
Once it just broke in the middle of the span from the pole to the house, and
once it broke right at the pole mounted transformer. the first time I had
no damage, the second time (when I was not even at home with anything on but
maybe a couple security lights) I had a couple of blown GFCI outlets - and I
mean BLOWN. Fire! Luckily the wallboard was not flammable, but there were
scorch marks, even on the kitchen cabinets. Utility paid off quickly, but
it didn't amount to much (maybe I should have put in for a new TV?)
How will that help? Do you really think the ground ROD does anything?
The only time the ground electrode will actually help with an open
utility neutral is if it is a metal water pipe, connected to metal
utility water pipe systems.
Even a Ufer, the best of all ground electrodes, is not going to sink
much neutral current in most places.
On Sunday, May 24, 2015 at 12:22:30 PM UTC-4, firstname.lastname@example.org wrote:
That has always seemed highly likely to be true to me, but I've not heard anyone agree.
A Ufer will always get you a favorable resistance measurement, but I've always had some skepticism about whether that translated into current sunk.
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