On 1/12/2014 12:45 AM, John Robertson wrote:
On 01/11/2014 8:41 PM, Mike Marlow wrote:
DaveC wrote:
The reason to use a contactor instead of just an on / off switch is
that the insides of the switch can get full of saw dust and turn on
the saw with the switch in the off position. I've seen this happen!
Regular AC switches are not sealed well enough, but you can buy
sealed switches with lower current ratings which is enough to engage
the contactor.

Shaun.

Best answer yet.

Yes, we all know about "during a power failure" but many times this
won't be an issue (actually the friend would appreciate the saw
continuing the cut after power comes back!), but the "auto turn-on"
feature )c: is one I hadn't thought of.

Thanks!

It may not get you much mileage with your friend. Despite the previous
poster's claim to have "seen this", you really have to consider the
likelihood of such a thing. Wood is an... insulator. Though he may have
"seen this", do you think your friend is going to believe it to be a real
enough possibility for him to consider? There are millions of simple
switches in shops all over the world - and they work. It would
probably be
hard to convince your friend their is a real risk here. For good
reason...


Wood may be an insulater but carbon certainly isn't. I suspect what the
provious poster was talking about was burnt bits of sawdust being
conductive. They would be burnt by the sparks present when the switch
was opened...leading to a potentially hazardous situation!

John :-#(#


Regardless, there is still electricity in that switch, just a lower
voltage. Burnt bits of saw dust can burn at a lower voltage sparks as
well as a higher voltage spark.

I suspect that the previous poster witnessed a defective or broken switch.


FWIW this links to the purpose and or how a magnetic switch/contactor works.

http://www.ask.com/question/how-does...contactor-work