I have an 220V air compressor (30A) in the attic of my garage.
It has a 110V automatic drain valve connected to it.
A the breaker box downstairs I want to be able to turn the power off to BOTH.
Ideally I could simply turn off the 220V circuit (the compressor is the only load).
The 220V circuit is single phase and the receptacle is a NEMA 14-50.
It is my understanding that this is a split-phase 3-wire system. It's really 4-wires: Ground, Neutral, Leg 1 (110V), Leg 2 (110V).
What I want to know is if there is any problem with me using one of the two legs (plus ground & neutral) to power a 110V outlet for the automatic drain valve. I'm 99% sure there's no technical problem. I just want to double check on any safety issue or something I may not be aware of (as a DIY).
Best Answer
Since I'm loosing confidence in the idea of using the single relay to control both circuits, I now think the right answer is to simply buy ANOTHER RELAY. I can get a less expensive 110v capable relay for the drain-valve circuit and wire them both to the same 24V signal from my digital IO controller.
This keeps all of the line voltage stuff "clean" and normal.
I'm not sure why I didn't think of this before.
[EDIT: 12pm 3/27] I'm 90% finished with constructing this thing. One more trip to the hardware store and the use of a my toner to find the 24v wire in the attic and it should be up and running. Here's a pic of the two pump-start relays mounted and mostly wired:
[EDIT: 7pm 3/27] Done! Works like a champ. Here are some pictures of the final result: