On Wed, 23 Jul 2008 12:21:52 GMT, (Doug Miller)
wrote:

In article cgFhk.374$DS3.189@trnddc01, Grant Erwin wrote:
Doug Miller wrote:
In article , Bob Engelhardt
wrote:

I'm in the process of modifying an electric clothes dryer. I want to
switch 21A, 240v current, but I don't have, and can't find, a switch
with that capacity.
My application will never require the switch to break the
current - that will be done by the dryer's timer.

Also, in a closed-contact situation, I'm thinking that paralleling 2
sets of contacts will double (more or less) the current capacity.


Assuming you're talking about North American standard wiring, that is NOT
correct. The two 120V legs that comprise a 240V circuit are not in parallel;
they are in *series*, and the current is the same at all points in the
circuit.

I think you may be misunderstanding Bob's application.

Not at all. I think you didn't read his post carefully enough.

Suppose you had
a single 15A switch in line with L1. When you toggle it, it will (obviously)
make or break 15 amps.

To clarify: it will make, break, or carry up to 15 amps *safely*. If 21 amps
is applied to it, it will make, break, or carry 21 amps -- until it fails.

Now suppose you put *another* 15A switch in parallel
with the first switch. Now if both switches are on, half the current would
flow through each. It's the switches that Bob is thinking of as being in
parallel, not the L1/L2 legs.

In the part you snipped, he wrote:

"So, if I use a 2 pole 15A rated switch, parallel its poles, & never
break the current with it, could it carry 21A?"

He's not even talking about two switches. He's talking about *one* switch,
and thinking that the L1 and L2 legs are in parallel. They are not.

Nope. He's talking about a DPDT switch. That is ONE switch physically,
but 2 electrically.

Also, FWIW, using two switches in parallel as you suggest is flatly prohibited
by the National Electrical Code.

Except it is NOT 2 switches. Relays are used this way all the time.

Still, as I have posted elsewhere, not the best solution - although it
WOULD work.

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