Just out of dumb curiosity, does this mean if you don't split off 120,
you don't need a neutral? Normally, with 120 you need 2 wires plus
ground, hot, common and ground. I don't know zip about 220 but are you
guys saying 220 can have 2 wires, both hot, plus a ground (no common),
and you connect one of the hots to the light, and what normally would be
common or neutral to the ground? I'm in the dark here, just asking.
Doesn't 220 always need a common ground (neutral?), just like 120?
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Exactly so. Pure 240V circuits (in North America) don't have, or need, a
No. It will work, but it's unsafe, and violates both the U.S. and Canadian
It's 240, not 220. And no, it doesn't need a neutral. 120 needs a neutral; so,
if an appliance has both 240V and 120V loads (e.g. electric stove: 240V
heating elements, 120V control circuits; electric dryer: 240V heating
elements, 120V motor) then it needs a four wires: two hots, neutral (for the
120V) and equipment (safety) ground. Pure 240V loads (e.g. a table saw or
welder) need only three: two hots and equipment ground. No neutral.
Doug, thanks for your clear reply. I use the same coloring book Leon
uses when it comes to electricity so any enlightenment is welcome. I
know enough to wire 120 circuits in my sleep, without killing me, or
anyone else so far, but
OK, but in my 120 coloring book, electricity comes in the hot wire, and
goes out the neutral wire, thus the circuit, or loop is completed. How
does this work with 220?
It sounds unsafe to me to be connecting a common ground to the safety
ground. In my small world, most of the time the safety ground is a bare
copper wire, not even insulated. In a 120 circuit, it would seem
anytime the load is hot, the common wire is carrying current back to
ground? Also, the motor frame, electrical box etc is connected to the
safety ground, would this mean the box/motor frame is hot whenever the
the load is on if you used the safety ground as a neutral wire?
In Somona's instance, he has his 240 motor hooked up, plus he has a 120
motor running the feed rollers. Assuming a 3 wire 240 hookup, he could
(unsafely, but common in the past?) hook one hot wire to the 120 motor,
and use the safety ground as the neutral wire for the 120 motor. If he
did this, the safety ground would always be carrying juice when the
motor was running, and ergo, anything hooked up to the safety ground,
the motor frame, wiring boxes and so on, would also be carrying juice?
Is that correct? If so, it sure sounds too dangerous to have been done
routinely for 100 years? I'm sure I'm missing something here, but hey,
I'm just trying to color in some of the pages:-)
I'm glad you said that. I was thinking damn, I don't even know if my
service is 110, 115 or 120? I see all sorts of things on electrical
devices. Even this thread is stating 220, or 2 110 lines? You are the
only one to correct it so far. No wonder I'm so confused... still alive
And no, it doesn't need a neutral. 120 needs a neutral;
Again, this confuses me. How is the circuit completed in a 240 circuit?
2 120 lines come from the source to the motor, then what? Where does it
go? I bet it has something to do with phase? Each line takes turns
being the neutral? If not, I'm lost, if so, still lost:-)
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simplicity think of the feed as -120V, 0, +120V. In your panel are two
bars which get the -120V, and +120V, the box is tied to the 0V, and
ground. This is now the only legal place where they are connected.
With a 120V breaker they hit one bar or the other, with a 240V breaker
both bars are contacted.
Back to colours, a 240V breaker by convention will have a black and red
wire connected to it, -120V and +120V giving a difference of the 240V,
if you bring along a neutral (white) wire there is the 120V option,
always carry the ground to the end of the circuit, but you can't legally
use it to get a 120V circuit.
Just like 120. The juice comes in one wire and out the other. The
difference is, with 120, one wire, the neutral, is connected to ground
so there's no voltage relative to ground on that wire. With 240, both
wires are isolated from ground and do have a voltage relative to
ground, +120 to ground on one wire, -120 to ground on the other, so
there's a voltage of 240 between the two wires.
(OK, if we want to get pick nits, the voltage is AC, so it varies in
each wire from +120 to -120 and back to +120, 60 times per second in
the US - hence 60 cycle AC. But when one wire is at +120, the other is
at -120. I would say the voltages are 180 degrees out of phase with
each other, but I'd probably be accused of claiming that 240v
residential is 2-phase service. And to pick another nit, those are RMS
values, not the actual instantaneous voltages. RMS = the square root
of the integral of the square of the instantaneous voltage with
respect to time over one cycle. Not sure of the actual maximum
instantaneous voltage, but seem to recall it's somewhere in the
neighborhood of 140 to 150 volts on each hot line.)
Same way. Really. Only difference is that the two wires have a 240V potential
between them, not 120V, and neither one is grounded.
Right -- but let's use some different terminology. The common-usage term for
what you call "common ground" is "neutral", and for what you call "safety
ground", "ground". The official terms as used in the National Electrical Code
(NEC) are "grounded conductor" and "equipment grounding conductor"
Correct. Sort of. It *is* energized, but since it's also connected to ground,
there's not nearly the same danger in touching it as there would be in
touching the hot wire. The danger comes from the fact that electricity will
follow all possible paths, and a person touching such an energized case forms
a second, parallel path to ground through his body. Such a path has a much
higher resistance than the copper wire, and thus passes only a fraction of the
current that the wire does. The problem is that 20 or 30 milliamps can stop a
Yes, that is correct, but as I noted above, the level of current that passes
through the body is much lower than in the copper wire.
It's nowhere nearly as dangerous as having the hot wire connected to the
equipment chassis. But it's also certainly less than fully safe.
Same way it's completed in any other circuit: by connecting together two
points that have a voltage difference between them.
You don't need a neutral for current to flow; you just need the two sides of
the circuit to have a voltage difference between them.
The utility company brings somewhere around 4KV to your utility pole,
connected to the primary windings of a step-down transformer. This transformer
reduces the 4KV from the utility company to 240V. There are *three* wires
attached to the secondary windings: one at each end, and one in the middle.
The two at the ends are 240V apart, and the one in the middle is 120V from
either of them. Let's color the wires connected to the ends of the secondary
coil black and red, and the one connected to the middle, white. There's 120V
between the black and white wires, 120V between the red and white, and 240V
between the black and red. Now tie the white one to a copper rod that's driven
into the ground, to ensure that it's always at true earth potential.
There's your 240/120 North American residential electrical service.
The U.S., Canada, and Mexico use substantially the same system. Almost nobody
firstname.lastname@example.org (Doug Miller) wrote in
So, for truly instantious table saw start up, we should hook the motor up
to the 4KV, bypassing the transformer. We'd only need a few microamps at
most to power it, therefore all the power we'd need go directly to the
Better add a cast iron body to the cast iron top, though... The slightest
imbalance might flip the saw over!
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
220V wired to a three pole socket has HOT1, HOT2, and ground.
Wired to a four-pole socket, it has HOT1, neutral, HOT2, and ground.
While generally considered poor practice, it was normal for many years
in the US for stoves and clothes dryers to have a heavy three-prong
plug for 220V 30A, and a small (fused 10A) auxiliary 110V circuit
that ran from one hot wire to ground. Safety code had an
"appliance exception" for this, and it was done because a 4-wire 30A
circuit and socket would have been excessive and expensive.
Think about it: there's gotta be a 30A ground wire for these items,
it carries NO current; to add a 120V 10A convenience socket, do you
to add a 30A neutral wire as well?
You generally need a ground but only need the neutral if you are using
the split phase (the 120V part). So, 240V will usually have three
wires (if there aren't any 120V loads) or four (with 120V loads).
Be careful, "ground" and "neutral" are different things. "Ground" is
used for safety purposes only. "Neutral" is a current carrying
conductor. If there is no current in the neutral (as is the case in a
purely 240V circuit) there isn't any need for the conductor. ;-)
By NEC it now does to be Code-compliant.
For roughly 100 years, split-voltage appliances such as ranges, dryers,
etc., used (and were Code-compliant!!!!) the ground as neutral for the
Only w/ a relatively recent Code revision was this changed to require
the 4-wire connection in all cases.
While granted it's not current Code, there are zillions of appliances
still in service and certainly a fair number of drill presses and other
machine tools wired the same way. There's absolutely no evidence they
have been a major safety issue in that time period.
Hence, while granted it's no longer within _current_ Code, there's
little real justification for that change being a big deal.
$0.02, etc., etc., ...
Not the way I read it--the whole thread was about split voltage circuits
and the question was about when needed a neutral as well as ground (or
at least that's what I thought (and still think) the question was)...
No. Speaking in the context of "normal" residential, single phase
120v/240v service, circuits that supply only 240v do not need or use
the neutral. Only the 120v circuits use the neutral wire. Multiwire
circuits that supply both 240 and 120 do need the neutral to support
the 120v loads.
Sorry, but that's not correct. At 240V, it will draw half the current that it
did at 120V. This will provide a much faster start, even if the 120V circuit
was properly sized.
More than "not supposed to do". It's unsafe, because it energizes the ground
conductor, thus energizing the chassis of *everything* that's plugged into
that circuit. Remember that electricity does not "follow the path of least
resistance" as many people believe; rather, it follows all possible paths.
That includes the path that goes through the grounding conductor to the
chassis of the saw to the saw table to the hands of the operator.
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