When did they stop? My electrician is in his 70's and he constantly
wires in what he calls "networks" with 12-3 (or 14-3) romex, running
two circuits with a shared neutral. The hots have to be out of phase,
of course, but if they were accidentally hooked to the same phase, the
neutral could get overloaded until it melts and starts a fire, and the
breaker wouldn't necessarily pop, since the neutral is unprotected.
Why would a double pole breaker be required without a 240v circuit?
In the unlikely event of an open neutral in the circuit, 240V would be
still be present across the hot leads. If for example a 15 amp motor
was running on one leg and a milliamp device on the other, the lower
current device would essentially be wired to 240V.
Make it as simple as possible, but no simpler.
Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
It may not be required (and maybe never was) to have a handle tie but
it would be a nice idea to keep home-owners from tinkering and moving
the wire to the same phase since this would force the red and black to
be on separate phases as it is required and shoot why not it doesn't
cost any more to get 2 pole breakers over 2 single pole breakers.
Also a problem I have been running into recently it that shared
neutral circuits will not support an arc fault or a gfci breaker as is
now required if your city is up to date on the NEC. Is it worth it to
save a small buck?
Thanks and keep the good questions rollin' in,
Lucas Electric, LLC
The reason I asked when they started allowing it again is because my
instructor said that code says you are supposed to use a double pole breaker
when sharing a neutral. I work for an electrician and we were wiring up a
portable gfci board for the local chili cook off and if we used separate
neutrals the pull through the carflex would have been more of a pain than it
was. I asked about the double pole and he said they said it was fine then
they said it wasn't then they said it was again. What makes me nervous about
the practice is when you are working on something and you shut the breaker
off you think ok I'm good to go. Now you go and pull down the light fixture
and start disconnecting it and get knocked on your ass because the neutral
is shared with the refrigerator circuit. If the 2 circuits were on a double
pull breaker the neutral wouldn't be carrying the load from the refrigerator
because both circuits would be dead.
That is true. In some cases having a double pole breaker is better,
like getting zapped by the neutral
Sometimes it is not better, like having the refrigerator go off when
you have a problem with the lights :)
a) your instructor is incorrect;
b) you misunderstood; or
c) your instructor is a Canadian. (AFAIK, this *is* required under the CEC.)
The double-pole breaker is required under the NEC if the circuit supplies
multiple devices on a single yoke, or supplies both line-to-neutral and
line-to-line loads. It is not required under other circumstances. [2005 NEC,
Makes me damn nervous too. My current house had three such circuits, all
unidentified, all on separate single-pole breakers. All Code-compliant and
perfectly legal, too, and I had no idea the circuits were sharing neutrals
until I happened to pull off the panel cover and see the red wires.
They're all on double-pole breakers now.
IMO a double-pole breaker should *always* be used on shared-neutral circuits
(aka multiwire branch circuits or Edison circuits), even when the NEC does
*not* require it, for exactly the reason you cite. It is IMO a foolish and
false economy to not spend the extra ten dollars on a proper double-pole
breaker, when failing to do so may cost a human life.
Doug Miller (alphageek at milmac dot com)
Seems this was a discussion about a year ago. It is a common practice
for electricians to use multiwire circuits. In 3 phase circuits 3 hots
can be run with 1 neutral. Requiring a 3 phase breaker and killing all 3
circuits to work on one would be ridiculous.
Most advice on this newsgroup, probably including yours, is to test all
the wires you are working on to verify they are dead. There are some
things that people should really know before working on electrical systems.
Use of multiwire circuits in residential is likely to go down
drastically with increased requirements for AFCI circuits in the 2008
NEC. (But AFCI circuits will not be required in as many locations as
Agreed, up to a point. Unless all three phases are killed, there *will*be*
current in the neutral wire if any load is operating on any phase -- of
course, 3-phase power implies a commercial or industrial installation, which
in turn implies that maintenance will be performed by qualified electricians,
who presumably have the required knowledge and equipment to work on live
circuits in relative safety.
I should have specified that my comments apply to *residential* multiwire
Absolutely. I go even farther than that, though: before testing a circuit that
you presume to be dead, test one that you *know* is *live*. If the tester
doesn't indicate, it's time for a new tester.
Doug Miller (alphageek at milmac dot com)
The NEC has a cousin - NFPA 70E "Standard for electrical safety in the
workplace" - which is somewhat of a defacto standard in most workplaces
covered by OSHA. The procedure in 70E is to test the voltage detector
before and after testing the circuit. But the circuit voltages and
energies can be so much more 'interesting'.
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