Short Circuit in cable in the wall

Discussion in 'The Projects Forum' started by jhausch, Sep 10, 2012.

  1. jhausch

    Thread Starter Active Member

    Jun 7, 2009
    49
    6
    I am motorizing 6 clerestory windows in my house. I am using the circuit attached x 6, but one of the cables seems to have a short in it.

    As you will see by the circuit, the switch pulls a relay closed and motors the window until the NC switch opens and drops the relay.

    The switch can then be left in position or moved to OFF until the opposite action is desired.

    The diodes at the motor are because I only pulled a 4 conductor cable when I built. As an electronics hobbiest/newbie, I thought that was a pretty clever solution, but I am not as clever as I need to be :rolleyes:

    One of the cables in the wall seems to have a short between two conductors.

    Since I can't fix the short without some major surgery, is there a way to fix this with some passive electronic devices? I have been playing with iCircuit on my iPad trying various resistors, caps, diodes, but I am stumped.

    Any ideas or suggestions?

    [​IMG]
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
    611
    120
    It's very unlikely to be a shorted cable unless you've knocked a nail or something through it? Sure it's not a wiring up fault, reversed or shorted diode, or something similar?
     
  3. jhausch

    Thread Starter Active Member

    Jun 7, 2009
    49
    6
    I am pretty sure it is a short within the cable. Could be a mfg defect, or (more likely) I damaged it when pulling or during construction.

    When it was all wired up (just the cable and the motor, the relay and switches not yet installed), I was able to run the motor in one direction using my power supply, but shorted out the power supply in the other (connecting at the motor or at the far end of the cable).

    I checked the diodes and resistance and it looked like a short in the wire, so I unwired the cable on both ends and got low resistance between the two suspect wires.

    I then checked the inner conductor jackets at the strip point of the outer jacket and found no nick.

    I assumed as you did, "Man, there is no way I have a short in the wall (grumble grumble...)". I now think I do.....(additional grumble...)
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,126
    3,048
    Since you can access both ends of the cable (right?), can't you use the old cable to pull thru a new one?
     
  5. Jeffnars

    New Member

    Sep 9, 2012
    19
    0
    If your sure it's shorted do the most simply option.

    Unwire both ends or the circuit, cut if needed and reconnect at a later date.

    Mke sure both ends are completely disconnected. Grab your meter and stick it on continuity.

    Go from wire 1 to wire 2' 1-3, 1-4 ect. If the cable is shorted then ull see it using the meter.

    Simple
     
  6. jhausch

    Thread Starter Active Member

    Jun 7, 2009
    49
    6
    Good thought, but too many twists and turns and "secured" points. Too bad it's not all in conduit.....
     
  7. jhausch

    Thread Starter Active Member

    Jun 7, 2009
    49
    6
    Thanks. I have confirmed there is a short.
     
  8. jhausch

    Thread Starter Active Member

    Jun 7, 2009
    49
    6
    I think I may have an idea....

    I could put a second relay (or use a DP relay) to control power in the circuit for the NC switch that stops the relay that is allowing motion...

    I may also need a diode in that circuit near switch to prevent backfeeding....

    Let me draw that up and post it...
     
  9. jhausch

    Thread Starter Active Member

    Jun 7, 2009
    49
    6
    Actually, that didn't work, but I think this will.

    I checked the amp rating of the limit switch when I got home. It says 5A at 125-250VAC. The motors I am using draw less than 2A at 24VDC when stalled. Running current is under 1A.

    THe diode around the switch allows a return path when trying to "get off that switch" going the other direction. One of the diodes around the motor is no longer needed, but I will probably leave it there.

    I will only need one of the 2 wires that are shorted together to do this. Just to be clear the "upper wire in the wall with the lightning bolt through it" will not be connected to anything on either end. What do you think?

    [​IMG]
     
Loading...