Trying to wire a gfi receptical with 14/2 w/gnd for a garbage disposal, in a very old house and the supply wire is not grounded, as far as I understand in electricity, you can't have a ground fault interuption without being grounded, also I tried and the receptical didn't work- it's got to be that, how do I ground this one circuit without rewiring the kitchen or messing with the breaker box, thanks in advance