Switching Postive/Negative

Thread Starter


Joined Feb 9, 2008
Im working on a circuit at the moment. It consists of timers and counters operating small relays. These small relays switch larger relays which drive motors and lights.
The small pcb relays are driven by a 5v supply and the larger relays have 12v coils.

At the moment it is much easier for me to tie the 12v coils to the 12v supply and switch the negative with the smaller relays allowing for a common negative between the 5v and 12v supplies. This means that I would not have to bring back a seperate 12v supply to the pcb aswell as the 5v.

Basically what I would like to know is would any problem arise by swicthing the negative instead of the positive on the larger relays?

Thanks for your time,
Regards NM


Joined Oct 15, 2009
typically no..however many times its best to switch the positive (or hot) lead just to prevent a shock if someone touched the unbroken power lead and the metal case or similar.