UPDATE: The wall box IS grounded via a wire that is screwed to the back of the wall box, and clamped to the Original 1953 galvanized plumbing in the wall behind the kitchen sink. I think it is the only grounded outlet in the house.
I plan to test the ground, replace the rusty wall box, reconnect the ground wire, and wire up the GFCI properly.
As a test, I pulled the outlet out of the wall box, plugged in the dishwasher, and measured 72V from the door to ground and to the neutral (not ground) wire. That seems odd. There is no measurable voltage on the door when the ground pin is grounded.
More Questions of course…
Is there a practical way to test & prove out the ground connection?
Is it sane to count on 70 year old galvanized kitchen sink plumbing to provide a robust path to ground?
Should i install a new ground rod and wire it to the box/outlet?
I found a copy of the 2020 NFPA chapter 3 electrical code, so i now have 1000+ pages of bedtime reading to add to the pile of books on the nightstand.
————— Original post below —————
I installed a dishwasher in our house for my wife’s birthday. Along the way I encountered two electrical oddities that I can’t figure out. I aim to have a safe and reliable system, and i am concerned that is not the case right now.
When the dishwasher was plugged into the outlet under the sink, running my finger along the door skin made a humming noise. I assume this means some voltage present on the door. In debugging mode, I took apart the 3-prong outlet and found there was no ground wire. Shunting white “neutral” to the ground pin “fixed” the humming, and the door felt like an inanimate object… a good thing.
But the humming bothered me and I decided to install a GFCI outlet under the sink. After wiring it up (black, white, and shunt from ground pin to white), the GFCI behaves as expected as long as it is outside the wall. That is to say, with nothing plugged in, the GFCI can be tested and reset successfully. But, if i go to install the outlet into the wall box, the moment the mount screws of the outlet contact the metal wall box, the GFCI trips.
Can anyone help me understand or diagnose what is causing the GFCI to trip? Is it reasonable to susoect any issue with the door of the dishwasher is either because of a problem within the (new, bosch) dishwasher, or because it is designed to work only with a ground wire in the outlet?
After reading about home wiring and gfci function, I have a theory that the neutral wire is not tied prioerly to griund at the panel. This might be allowing its voltage to float a lottle above ground. When the gfci is grounded to the wall box, the potential difference between neutral wire and ground causes current to flow through the neutral wire. Since nothing is plugged into the outlet, no current flows through the black (hot) wite. The gfci detects the difference in current flow between the two wires, and trips.
Bottom line: Do i need to do any diagnostics on the dishwasher itself? Or is it reasonable and safe to assume if it works properly and the door isn’t powered when plugged into a grounded outlet, that all is well with the dishwasher?
How can i figure out what is causing the GFCI to trip, and how can i fix it?
What other questions or approaches would you suggest i consider?
Thank you, Paul