Same as anywhere else. It's not the voltage, it's the number of phases.
If you use single phase (and "domestic" always does) then you need a
neutral. This isn't because you "need" it as a consumer, just because
it's the convenient way to tap a supply transformer for a single phase
If you use multi-phase (i.e. three phase), then you don't need and
don't use a neutral. There's just little point to it.
If you choose too low a consumption voltage in designing a system-wide
standard (i.e. 110V) then it becomes necessary to also provide a high
"high power domestic" feed of twice this, hacked together by using
opposing phases of a two phase supply. You don't even need neutral here
either. It can be useful though for loads that are easily split in two
(i.e. heating elements) and is naturally provided if the "double
voltage" system is already providing a neutral connection to the supply
transformer's centre tap.
That's not a 3-phase system, it's a combination of 3-phase and single
phase. Only the single phase component needs the neutral to supply
power, but because it's also bonded to the local earth it's supplied as
well. It's sometimes used for the provision of separate heating
elements on each phase, also with electrode boilers so as to limit
potential difference between the water and earth.
How do you figure that? The three phases are tapped off a rotary generator at
the power plant, 120 degrees apart, with the neutral as earth ground. Any one
of the three phases can be used separately, of course, but there's no
Might be different in the UK, but there isn't a separate "single phase
component" in North American three-phase power distribution -- 120V devices
are powered by using any one of the three phases, and a neutral which is
bonded to earth ground.
208V devices use any two of the three phase conductors, or all three, and no
Doug Miller (alphageek at milmac dot com)
That's what I'm telling you. Both systems are wired through similar
cabling, but the neutral only gets used when it's supplying a simgle
And the "208V 2 out of 3 phases" unbalanced systems are an abomination
unto the hallowed memory of Tesla.
That is correct. That configuration is visible at the transmission
The very basic reason for that, is the attainable rpm of either 2 or 4
4 Pole being the choice of large diameter (1800 RPM turbines, lest the
turbine blade-tips break the soundbarrier.)
Anything that has just a 240V motor does not need a neutral. But
accessories such as lights do. As electronic controls on tools will
become more common, I would expect more of them to need neutrals.
Just because you run 4-wire cable does not mean you have to install
the much more expensive 4-wire outlets; those can be retrofitted when
Side remark: What everyone calls neutral (on a 120/240V circuit), the
electrical code calls the grounded conductor. What everyone calls
ground, the electrical code calls the grounding conductur. The
difference is small, but crucial.
If you don't want to do it twice, then run 10/3 (with ground!) now.
Even better, in a few places where you might want to add high-powered
tools (such as a 5HP table saw), run 8-3 instead; the cost is only a
little higher. Ideally, you should run conduit (3/4" EMT is better,
as it is easier to pull #10 and #8 wires through it); but installing
conduit in an existing stud wall is a big pain, and flexible conduit
is really hard to pull through. While you are at it, terminate all
240V cables in extra-deep metal 2-gang boxes (not plastic), with mud
rings. Then you can later replace the single-gang mud ring with a
2-gang mud ring, and install larger outlets: trying to squeeze a 50A
4-wire 240V outlet into a single-gang box is either impossible or very
hard, and certainly violates code.
If you mean by this that you can use 10/2 with ground wire, and then
at the device end use the ground as both a neutral and a ground, you
are absolutely wrong. Yes, they may be connected at the breaker box,
but by no means on all breaker boxes (read the electrical code, in
many cases they have to be isolated from each other). Deliberately
running current through the safety grounding wire is extremely
dangerous, bordering on suicidal. Extremely bad advice.
While we are at it: I would recommend GFCIs for everything in a shop,
in particular if the shop has a concrete floor, is in a basement, or
has any risk of getting wet. 2-pole 220V GFCI breakers for the
electrical panel are inexpensive and easy to find.
The address in the header is invalid for obvious reasons. Please
reconstruct the address from the information below (look for _).
Don't skimp. Do it "Right" the first time. Use 10/3 with ground and be safe;
safer; ready for change, not sorry.
Also, the circuit can be used to pull a 110/120 outlet as well.
Do it to "code" and you will not be sorry.
I know the cost of wire is nuts nowadays, but the old rule "do it right the
first time" has proven itself may times over to be the best advice.
If he were to do it "right" the first time, he'd use 10/2 w/g.
If you were to wire a separate 110v outlet from this (instead of
using a 4-pole receptacle), you'd be in violation of code, since
the breakers are handle-tied (which would prevent one from being
able to disconnect the 110v circuit without also disconnecting the
While this is generally true; doing to the specific requirements
of your jurisdiction is better.
While one may wire a circuit for a specific tool, the circuit doesn't know
hat. Not might others who subsequently own that circuit (as when they
purchase the home).
Circuits installed in homes are, therefore, just 110/120VAC or 220/240VAC
circuits terminated with breakers and receptacles that would appear to
indicate the design amperage but in no way indicate which "tool" the
installer initially had in mind when adding the run out to the portion of
the home the installer might have used for a workshop or sauna - who knows?
I bought a hoe that saw its share of homebrew re-wiring all of which may
well have minimally served the installer at the moment but had seen adapted
to serve uses beyond the limits a strict interpretation of the electrical
codes I'd come across in dealing with several inspections and inspectors in
South Florida over the years.
As I cannot find the NEC on-line (save in offers to sell me a copy for sixty
bucks or so), I've been unable to find and cite the advice recalled from
various and sundry wiring projects involving City Electrical Inspectors who
were able to quote me the relevant code at the time.
So, I may well be advocating over kill in insisting that OP consider running
10/3 out to his shop to support a motor that only demands two hot conductors
and an equipment ground to actually operate (indeed, will do so without
running the equipment ground others have chimed in to support installing).
Part of my issue, aside from exculpation clauses in insurance policies an
the potential liability to a subsequent purchaser under law, was the
practical matter of expending the additional cash to cover the cost of the
neutral conductor out to the intended outlet in anticipation of the one
constant all reasonable wood workers can agree upon - change.
As, if and when I can find the code book, I shall look up a residential
240VAC circuit and report what I find verbatim (since no one else seems to
have access to the code to do so not withstanding the ad hominid attacks in
response to my prudent suggestions herein.
So for those vociferous folks who would find me so fallible and my advice to
go with 10/3 rather tan 10/2) so offensive, ignorant and objectionable as to
warrant attacks on my credibility, intelligence and motives, let me agree to
disagree an leave it there.
I must admit that the insurance and legal points made were a bit "out there"
in the sense that such cases seldom arise unless the loss of life is
significant and the pockets of the liable party are obviously deep.
But, in my defense, we were notified that the crack in the pane of the
window in our garage would result in the cancellation of our policy if not
corrected in two weeks! Good thing they had not inspected my electrical
Before one blithely assumes he is "covered" by his homeowners, perhaps a
review of what happened to all those folks in Louisiana an the Gulf Coast
after the Hurricane. Disputes over whether rising water or wind-driven water
caused the damages with the majority of the insured walking away with little
or nothing despite their coverage. Talk about your exculpation clauses!
What if the motor of the intended device would operate upon two twelve's -
would that be OK as well?It would be less expensive.
I suspect the OP has long since abandoned reading this thread as I should
and will forthwith as my intent was not to antagonize those with as much
time on their hands as I but to offer well-intended advice to a fellow
carpenter the result of which could not be assailed as unsafe, dangerous,
nor imprudent only unnecessary.
Equipment is typically provided by its manufacturer with a plug that is
appropriate to that equipment -- a plug which prevents connection of that
equipment to a receptacle that is not suitable.
You'll excuse me, I'm sure, if I smile a little bit here, as your previous
posts don't indicate any degree of familiarity at all with the NEC, or indeed
with residential wiring practices in general.
Read to your heart's content, and try to back up the silly claims you've been
You didn't just insist that he "consider" it -- you insisted that it was
required by Code.
You haven't cited any of those, either.
That won't be necessary -- simply citing the relevant article and section will
do, since all of us have the same access to it on-line that you do.
Again, the full 2005 NEC is at
You haven't made any "prudent suggestions" -- just uninformed claims about
supposed Code requirements that do not in fact exist.
You've ruined your own credibility by making unfounded and erroneous claims
about phantom "requirements".
Doug Miller (alphageek at milmac dot com)
One other point: Insurance.
If there's a fire, etc. and the investigation uncovers your home-brew
cost-saving electrical work, your insurance company can simply deny your
claim because you promised them you would never install electrical without a
permit, licensed contractor and appropriate inspections.
A missing neutral would be hard to disguise!
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.