# Can relay source and switching source be the same?

I'm working on a schematic for a power supply system for several linear actuators. I would like to minimize the power supplies needed to run the system. Can the source used to switch a relay be the same as the source for the load on the relay? I don't think so, the eStop in the diagram below isn't rated for the load on the relay. eStops aren't designed for high current. In the schematic below it seems like the estop would be exposed to the current draw of the load. Just want to check my assumptions. Thank you!

• As long as your coil voltage match, I see no issues. Any particular reason you are switching ground instead of +12 V? Commented Sep 16, 2021 at 15:44
• No reason in particular. Is there a downside to one way or the other? Commented Sep 16, 2021 at 15:59
• It's probably minor, you have more the circuit energized (compared to switching the hot side) so that if there is ever some random event that happens to short part of the circuit; you have higher probability of it being the energized side, and without fuses (your drawing shows none) bad things can happen (melted wire, etc, etc,). Commented Sep 16, 2021 at 17:36
• +1 what Tyler said. Unless you have a British positive ground car. Commented Sep 16, 2021 at 20:41

The pushbutton only needs to drive current to relay coil to actuate it. That might be in the order of 0.1A. The relay contacts are the ones that need to handle the 80A load. So of course you can use the same 12V supply to drive a 12V relay coil.

Can relay source and switching source be the same?

Yes.

Any particular reason you are switching ground instead of +12 V?

No reason in particular. Is there a downside to one way or the other?

No problem, should a source terminal not be grounded (either +ve or -ve e.g. as in an automobile).

Should a source terminal be grounded, switching the ungrounded side is a must to prevent an earth fault from switching on a load.

Here's the conventional circuit that would also be okay for negative ground.