ECN Forum Forums General Topics of the Trade General Discussion Area Mysterious Shock

Sounds like Capacitive Coupling - or the Control Circuit's Grounded Neutral Conductor has become re-grounded at or near the Heat Pump.

Simple test to verify the issue is due to Capacitive (or Inductive) Coupling:

1. Check Voltage between the Ungrounded Conductor and the Equipment Grounding Conductor ("EGC") with a High Impedance Voltmeter (typical DVM),
2. Shunt one of the Conductors to Equipment Ground via a low Impedance (i.e.: Incandescent Lamp, Solenoid Voltage Tester, full roll of #12, etc.)
   BTW "Shunt To Equipment Ground" = connect the Low Impedance item between one of the Ungrounded Conductors and the EGC
3. Check Voltage again between the same Ungrounded Conductor and the Equipment Grounding Conductor, with the same High Impedance Voltmeter,
4. If the issue is Cap / Inductive Coupling, the 40 - 50 VAC will be reduced to, or near zero Volts.

If the issue is not due to a Coupling Effect, and not due to a re-grounded Neutral, call an exorcist!!!

--Scott (EE)