Originally Posted by bruin_ale
That's the most common usage for the contactors. They aren't DPDT though, they're DPST (two poles, either on or off).
You can get DPDT contactors. One set of NC contacts and one set of NO contacts is how they are implemented... I think.
but, for an on/off switch, DPST is sufficient (and cheaper probably).
When I got mine, I was able to buy them on ebay for less than $7 shipped. Looks like they are going for more than that now.