wrote in message
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On Jan 17, 12:32 pm, "Buerste" wrote:
"Gary H" wrote in message

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On Thu, 15 Jan 2009 23:12:14 -0500, "Buerste" wrote:

"Tman" wrote in message
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Took a look at the schematic today for the dryer (240v). I've always
wondered how they serve up 240 V with 120V components (e.g. timer
motor)
on only three wires.

You see, I always thought that the grounded conductor should never be
current-carrying, in the theory that if the ground feed should break,
then
the metal chassis of the appliance does not get energized.

Well looks like that "3rd" wire, is a neutral, and judging by the
dryer
schematic, is both used as a chassis ground and a current-carrying
conductor for the 120V items on the dryer -- such as timer and drum
motor.

OK -- am I totally wrong about the code and theory, or is this unsafe?
Seems to me that dryer would get real "hot" should their be a fault in
the
neutral conductor to the breaker box.

I know I'm missing something here as this is SOP as far as I am aware.
Someone please inform me?
T

Google: "Split Phase"
In a nutshell, the two hots are 180 degrees out of phase with each
other.
The potential between either phase and ground/neutral is 120v. The
potential between the two hots is 240v. A single phase of Alternating
current looks like a sine wave on an oscilloscope with the wave swinging
up
and down. With split phase, it looks like 2 waves on the scope. As one
wave is bottoming out the other is topping out. They are like mirror
images
of each other. If you measure the peak of either wave to ground, it is
120v

Actually, the peak is 170V (RMS * 1.414) but you don't need reality to
get in the way here :-)

if you measure the top peak of one wave to the bottom of the other, it
is 240v.

340V. Shut up, reality :-)

There, clear as mud! Any 240v device will run on just the two
hots, any 120v device will run on either hot and ground/neutral.

I understand, however to make it a bit clearer I used numbers that more
easily translated to the OP's ability to understand. Sorry I wasn't more
technical, do you think he would have understood your numbers better in
relation to his dryer?- Hide quoted text -

- Show quoted text -

To the OP, you are exactly correct, the 3 wire system can be dangerous
if the "ground neutral" wire opens becasue most dryers have a 120 volt
motor so that current flows through the neutral ground. NEC code as
picky as it is used to allow this. I think it is now not allowed in
new homes. I have a 3 wire dryer and I added a ground wire connected
from the frame of the dryer to the frame of the washer. This way,
whatever else happens there can be no voltage across those two
appliances and the washer has a 3 prong plug so it is grounded. You
can also connect it to a cold water pipe. I would suggest you do that
as an extra saftey feature.
Good question
Mark


I would recommend using a 3 wire dryer circuit just as it was intended to
be used or replace it with a proper 4 wire system. Installing a Rube
Goldberg grounding addition isn't helping the situation, and could
potentially cause more harm running line voltage fault current through your
plumbing or other appliances