Measuring voltage in garage breaker box

Discussion in 'The Projects Forum' started by nutra, Sep 2, 2008.

  1. nutra

    Thread Starter New Member

    Sep 2, 2008
    I have a 60AMP sub-panel in my garage running from my house.

    How do I measure the voltage in the garage breaker box?

    Reason: I want to run a line from the garage box to a hot-tub I am installing. The manufacturer recommends a 50amp GFCI to feed the tub.

    I want to know what kind of voltage (due to voltage drop) will be available. How long can I go with the wire from the garage to the tub and wht gauge should I use?

    Feedback would be greatly appreciated.


    Last edited: Sep 2, 2008
  2. SgtWookie


    Jul 17, 2007
    You really need a qualified electrician to review your current wiring, make recommendations, and perform the installation.

    Trying to do this "on the cheap" may result in your home becoming a burned-out shell, and the insurance company refusing to pay due to incorrectly installed/sized wiring/boxes/etc.
  3. nutra

    Thread Starter New Member

    Sep 2, 2008
    I agree .... an electrician will do the connecing ...... I just want to know what to buy and for that, I need to know if i will need to run it from the house OR can run it from the garage.

    From the house: 240ft of wire.

    From the garage 110 ft.

    How would I measure the voltage in a 60amp sub-panel using a Digital Multimeter?

    I want to determine how much voltage drop is occuring along the powerline that is running from the house.
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    The voltage drop from the house to the garage depends on the load in the garage. Drop across the feeder is equal to feeder wire resistance times current through the feeder. So, the more stuff you have plugged in and running in the garage, the more current you draw, and the higher the voltage drop. If you are not drawing any current at all, there will be no voltage drop across the feeder wires at all.

    We can estimate the resistance of your feeder wire if we know the distance between your house and your garage. AWG#4 wire is about 0.25 milliOhms per foot. Remember: you have one wire running to and another running from, so multiply the feeder lenght by 0.0005 Ohms to get a proper resistance estimate. (This again assumes AWG#4 wire). At 60Amps, that would work out to a drop of 0.03V per foot, 0.02V per foot at 40A, 0.01V per foot at 20A, etc.
    Last edited: Sep 3, 2008