** Frank ** wrote:
"Don Young" wrote in message
...

"** Frank **" wrote in message
...

"Jeff Wisnia" wrote in message
...

** Frank ** wrote:

I have a clothes dryer with a 120VAC push to start button. In measuring
the terminals, both sides are hot (120V) with respect to ground and
zero volts across the two terminals. Why is that?

I thought there was a short on one side of the push button but the
dryer is working properly. Normally it should be hot only on one side.




We could make more intelligent guesses if the OP told us whether those
measurements existed with the dryer running, off or either.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.


The push button is normally open. Measurements existed with dryer off.
Push to start means the contacts short across the terminals. I use a very
old but reliable analog Simpson 260 meter for the measurements.


I think, as some other posters have mentioned, that once the button is
pushed the timer, a relay, or a centrifugal switch on the motor closes
contacts in parallel with the switch. This keeps the dryer running after
you release the start button. It's a common system used in motor controls
with seperate start and stop momentary pushbuttons. However, this would
require your measurements to have been made with the dryer running.
Basically, if there is zero volts across a normally open switch, closing
it cannot do anything, as would be required for the dryer to start when
the button is pressed. You might want to check your measurements again.
There could be a schematic diagram somewhere inside the dryer.

Don Young



The schematic shows the PB is in parallel with the motor relay NO contact
and a solid state circuit board called "even heat control". After start up,
the PB is sealed by this motor relay contact providing 240V across the motor
windings. No ideal why both sides of the contact are at the same potential
before start up - goes against theory. Too many other things to do right now
but when I get around to it I'll open the control panel up and measure it
again.



Looks like you and I both have curious minds....

And als Simpson 260s...Mine has been with me almost 50 years now. G

Do let us know what the answer to the mystery turns out to be.

But my curious mind also wants to know what prompted you to make those
measurements in the first place... G

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.