Relays and Contactors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Richard Williams by way of Terry Fritz <twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>

Hi list,
 
Ok, I'm new at this sort of thing, high current household voltages, 120vac and
/or 240vac.
 
I plan to be able to interupt power from the mains using a deadman's switch
controlling a relay or contactor.
 
During the past I've seen arcing from connections being pulled apart, or any
situation interupting high currents.
The planned current load will be 240vac -at- ~20amps continuous duty. What would
prevent excessive arcing when the contacts open under full load? Is there a
difference between relays and contactors in this respect? 
 
I will be using variacs to ramp up power and back down again but if the
deadman's switch opens at full power....??
 
Rick W.
Salt Lake City