I have electric running to my barn that has been in place for 5 years with no issues. This year when we plugged in the tank heaters the horses are getting shocked. I tried disconnecting all other circuits and tested with just that one circuit and it is showing 3.5 volts in the water. It's there even if the breaker is turned off and the heater is in the tank. Disconnected the black wire in the garage panel and with the main breaker in the garage panel turned off, I get the 3.5 volts when testing between the neutral bar and the black wire. Turned off the circuit in the main panel in the house going to the garage and again, still getting voltage coming through. Any suggestions??