120V on fridge door handle when ground broken

Question

Looking at a friend's fridge that I discovered had a broken ground pin in its power plug

Fridge chassis was causing painful shock when touching it. I measured 120V from fridge chassis to ground. I found the ground pin missing from the plug, and assumed a damaged wire in the fridge was energizing the chassis but inspected inside fridge and all wiring was in perfect condition.

Connecting the fridge chassis to ground did not cause a short circuit. I replaced the plug with a correctly wired one and the fridge functions normally and no longer causes electric shock. Plugging the new plug into a nearby, tested, GFCI outlet does not trigger it.

I'm aware of phantom voltage caused by inductance that can be measured with meters and aware fridges can sometimes have some current to ground through inductance but never heard of or experienced it so significantly it would cause painful electric shock. And, that theory would suggest A GFCI would be triggered.

Any understanding of what might have been going on, and whether this is normal for a fridge with severed ground connection or whether there may be some remaining fault with it now that the plug is repaired and there are no symptoms?

Answer 1

It only takes a few mA at 120 V to get a noticeable tingle. You've already determined that the current leakage is very low -- too low to trigger a GFCI -- so if you want to track this down further, you can disconnect the ground wire from the new plug and place an AC milliammeter in series between the ground wire (or the metal chassis itself) and the outlet's ground to actually measure the leakage current. It would be best to use a fused milliammeter if you have one.

How about that old analog Micronta Range Doubler that you haven't touched in years? Perfect for this task.

Once you have a good handle on the actual current, you can try various measures to isolate and identify the source of leakage by monitoring the meter display while disconnecting refrigerator components.

• See if disconnecting the compressor's capacitor (if any) makes a change.
• See if the current changes or disappears with the compressor running / not running.
• See if unplugging the compressor's electrical connector makes a change.
• And so on with the defrost timer, defrost heater, mullion heater (embedded around the door), ice maker, circulating fan, light socket, water/ice dispenser, control board, and so on.

Something, somewhere in the refrigerator is leaking current, so if you can measure it and display it continuously, you'll be able to find it.

Answer 2

Most appliances are hard to check all of the wiring.

Chassis to anything should read 0. 120v to ground means hot is touching chassis somehow.

You need a good connection between hot/ground or hot neutral to cause a breaker short trip. Most breakers will be quite happy not to trip with a partial short. 7 amps for the fridge and up to/just above breaker size to ground. Lost money.

Most of us do not have the special testing equipment to check for bad wire insulation.

Imagine plugging it into a GFCI protected circuit will pop the GFCI. This is what GFCIs were made for. Partial shorts that might kill, but not trip a common breaker.

Grounded or not, the chassis should not give a shocking experience without a problem in the wiring.

Instead of the fridge costing 10 dollars a month, it is now costing 50 to 100 dollars since the ground is bleeding off power.

Answer 3

A power supply designed to use ground for EMF noise suppression but severed from ground

Picking up on @AndrewMorton's comment above and making this a Wiki answer because I doubt I'll have time or access to experiment or to ever understand this conclusively.

Andrew asks: Is it a simple fridge or does it have some electronics in it, such as a digital temperature display? Maybe the electronics have a switched-mode PSU designed to use ground for EMI suppression. Without the ground connected to ground, there could be a noticeable voltage on the chassis

Answer: *This* fridge has an electronic front panel and LED lighting.

SMPS Noise suppression: Here is a decent article on SMPS noise suppression and leaking to ground. There are a lot of really bad and misleading articles out there. Watch out. Basically there are articles like "Electricity! Danger! Double Insulation! It's all about safety!" and then there are articles requiring at least two years of undergrad Electrical Engineering, but very little in between. If you find a good "in between" article please add it here.

Zap Lap: I have experienced this! When a laptop computer is fed by a power brick with a two-pin electric plug, you wear shorts, put the laptop on your lap and feel a tingle from the screws on the bottom. I have also experienced it with a three-pin brick plugged into a two-pin outlet. It's unpleasantly painful. Here is a blog by Dell themselves, acknowledging the problem and their fix, but using evasive and euphemistic language to avoid saying you are being subjected to electric shock. Almost all newer laptop computers now come with three-pin power cords, where the third pin is bonded to the Negative side of the DC output.

It's very reasonable for the designer of a feature-packed modern fridge to assume it will be grounded properly, and design for that. I have no proof yet and maybe next time I pull my own fridge out for cleaning I'll test it with a cheater plug for a little more evidence.