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Simple electrical question ** Frank ** 07-17-2007
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Posted by ** Frank ** on July 17, 2007, 12:33 pm
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.




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Posted by Jeff Wisnia on July 17, 2007, 1:32 pm
** 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.
>
>
>

Not really a simple question...Your description leaves me scratching my
head.

What are you measuring those voltages with?

If it's a meter, what kind, digital or mechanical movement?

Can you locate a schematic diagram of the machine wiring? That should
tell the tale.

Jeff

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


Posted by Jeff Wisnia on July 17, 2007, 1:42 pm
Jeff Wisnia wrote:

> ** 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.
>>
>>
>>
>
> Not really a simple question...Your description leaves me scratching my
> head.
>
> What are you measuring those voltages with?
>
> If it's a meter, what kind, digital or mechanical movement?
>
> Can you locate a schematic diagram of the machine wiring? That should
> tell the tale.
>
> Jeff
>

Could be there's an electrically latched relay is the setup which closes
a set of contacts that "short" your push to start switch. When the dryer
is stopped by the timer running out or someone opening the door, power
to the starting circuit is cut off and the latching relay drops out.

Capice?

Jeff

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


Posted by dpb on July 17, 2007, 1:33 pm
** 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.

First guess is there are more terminals and you're measuring two inputs
or an auxiliary feed/interlock.

Second is perhaps you're using a high-impedance meter and one of these
is a so-called "phantom" voltage...as Jeff is getting ready to try to
determine. :)

Try a neon tester or a light bulb on a set of leads and see if the
voltage is still there on both terminals if there really aren't any others.

--

Posted by Paul Franklin on July 17, 2007, 6:34 pm
On Tue, 17 Jul 2007 09:33:24 -0700, "** Frank **"

>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.
>
>
Any chance it's a normally closed pushbutton? If you press it when
measuring across it, does the voltage go from zero to 120?

Seems odd that they would use a NC switch, but that's the only thing
that explains what you measure...

Paul F.

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