DIYbanter - View Single Post - How do I know if I need a new switch for 240v?

In article , says...

"LRod" wrote in message
...
On Thu, 27 Apr 2006 07:55:21 GMT, "Toller" wrote:

"Steve W" wrote in message
. com...
I have a Delta hybrid TS (36-715) and just wired it for 240v. Now the
thing starts up so fast it makes me worry about belt wear.

If it doesn't say on the switch, you can tell by measuring (after the
switch, with the switch on off) the voltage from each wire to ground. If
either is 120v, then it is a 120v switch.
That explains why you need a 240v switch. While the tool works fine
either
way; a 120v switch leaves wire energized that you would expect to be dead.

Even a SPST switch is technically capable of switching a 240V device
on and off--if any break occurs in the circuit (that is, either leg)
the motor will not run. That is what you alluded to. There has been a
fair amount of debate here as to whether that's a good idea or not.

However, if the switch contacts are only rated for 125V service it's
not a good idea to employ the switch for 240V use irrespective of
whether it's a SPST or DPST.

Now, to answer the OP's question, I would be very surprised if there
wasn't any voltage rating marked on the switch. I would have thought
that a requirement. In any event, I believe one of the other poster's
answer is probably a good idea--contact Delta.

You are FOS.
A SPST is not a 240v switch in this country, even if it is rated for 240v.
If you look at a SPST circuit breaker it says "120/240vac". By your
reasoning you could use one to protect a 240v circuit. It would work,

Take a look at some of the new contactors being used to switch air
conditioning compressors on/off. Some of the new ones only have ONE
contact point, yet they switch 240 VAC on/off all the time. Personally,
I don't like it but it works because current only flows when the two
legs form a circuit. Interrupt either one and you break the circuit.
The same thing would happen if you put a SPST in one of the 240 VAC
legs. I certainly wouldn't suggest that, but it'd work -- for how long
I don't know as the switch contacts might not handle the current load
for very long. My suggestion -- CONTACT DELTA and don't give up until
you talk to someone you trust!