Wiring common ground

Discussion in 'The Projects Forum' started by Edmunds, Jun 12, 2011.

  1. Edmunds

    Thread Starter Active Member

    Sep 27, 2010
    Hi all,

    The following challenge:

    I'm wiring up my motor home with lots of stuff. A 5V step-down converter (from 12V) to power Apple TV and Airport Express and 18V step-up converter to power Mac Mini. Both PSUs will be powered from the same slot on the control panel, same fuse, wired in parallel. Some time ago, I have led three wires up to the actual consumers (bloody difficult) - black for ground, orange for plus and another orange "just in case". As I did not know about the 18V requirement, "just in case" seem to have happened. Now the question is, if I can use the same wire for ground from both PSUs, or I have to lead another ground cable up. If yes, would be great if somebody can explain why. If no, same thing.

    Thanks' a million.

  2. #12


    Nov 30, 2010
    Seems like "yes" to me.

    I have trouble imagining why it wouldn't work, but on this site...you run into all kinds of "What were you thinking?!" Maybe I'll get bolder after the coffee kicks in.
  3. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    will it handle the current requirement?
  4. #12


    Nov 30, 2010
    I tend to assume that other people know what I know, and it's not true. Your power supplies can probably be configured to use the same ground wire, if the wire is large enough. It seems obvious to me that you just connect the grounds together and run the voltages on seperate wires. Try it. If a fuse blows, check back here. (You do have a fuse block, don't you?)

    I have to go to work now.
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    As long as the motor home voltage is coming from a battery source, and not an independent(floating in reference to the cabin electrics) supply, the common is just that; COMMON.
  6. someonesdad

    Senior Member

    Jul 7, 2009
    Just to clarify, the answer is "yes" because it just references the supplies to a common reference voltage. But, as others point out, you need to make sure that the wire you use for the common can handle the sum of the converters' input currents. If you give the size of the wire and the measured input currents of the two converters, we can give you an opinion on whether the wire size is OK.

    Oh, and if you haven't done it yet, put some unambiguous and permanent labels on those two orange wires (both at the source and destination), because sure as hell you'll forget what they were for later (ask me how I know :p).