What kind of switch do I need?

[unclecritic]

An option for a timer could be a relay between the dpst and spdt that is controlled by a light timer. Could get a pretty fancy timer if you wanted. RIB relays are pretty easy to work with, they are cheap, they have quite a variety, and ive seen them rated for 2hp which should be plenty. I think they even have some with dry contacts to simplify wiring so you could just use a simple rotary timer. Google "rib relay"

[LCHIEN]

You want what they call an auto-off timer. THe one below is by Intermatic, mounts in a wall switch box. Available I think in 0-15 mins, -0-30 mins, 0-60 mins, 0-4 hours, 0-12 hours and some other ranges. They have spring clock movements so they're very simple and reliable.

http://www.amazon.com/Intermatic-FF1...5591728&sr=8-6
AT Amazon you can search for Auto-off timer


I would recommend for air cleaner use 0-4 or 0-12 hours. I have 0-12 hour auto-off switch from Lowes for about $10 on sale once. I usually set it to four or six hours when i enter the shop, it runs long after i go back to the house to clean up any dust still floating around. ANyway, much easier than trying to build your own timer from a 555 IC.

they have 2-pole if you want it (~$50)

[chopnhack]

Good thinking Unclecritic, I had drawn up three or four sketches and none had that scenario in them! Thanks for your input :-)

Thank you as well Loring!
I had seen these timers, but didn't realize they were spec'd as high (current wise) as some are! The FF12HHC seems to be a winner. I guess I can do without the added safety of the dpst, it was for piece of mind. Hopefully if the unit is labelled as 240v, someone would be wise enough to throw the breaker before servicing

Certainly much easier than the 555, I had forgotten how inaccurate they are since they are still based off of the discarge of a rc circuit!

Edit: Does anyone have a source to lookup the NEC on 240v motor wiring - I seem to remember that you didn't have to switch both leads in (both sides of the split phase) can anyone confirm or deny? The intermatic instructions for the switch seem to show 240v motors having a DPST switching both sides!