Earth Leakage?

[deafwish]

A strange one, but please bear with me here...

I was kneeling next to my Bravo 3 yesterday and when the soft part of my arm touched the prop's, I'd get an electrical tingle through my arm.
It's only when my (near new) 5 amp CTEK battery chargers (one per battery) are plugged in and I've wired them directly to the building's power outlet to eliminate the boat's shore power - it still tingles my arm.

I got my multimeter & grounded it on my pickup truck and got 50 millivolts (1000 millivolts to a volt) on the prop.
Disconnect the batt charger & get 150 millivolts & no arm tingle?!
I can replicate this every time.

I have a Mercathode and was wondering whether this small voltage is normal & whether it changes when a charger is connected?
Any tips?

 

[GA_Boater]

What does the truck have to do with this? Are you using the truck to power the chargers?

What happens if the shore power is used to power the chargers?

 

[dratlief]

You could have a current back feeding through your ground wire into your chargers at the building plug.

Assuming the boat is on a trailer (with rubber tires) the boat / engine and drive assembly are isolated from ground (do to the tires) so your body completed the circuit to ground when you touched your arm to the prop.

​Your truck is sitting on tires, therefore, as noted above, I don't understand how you could be getting a circuit?

Some out buildings don't have ground rods. A ground rod with a proper sized wire should be attached to the common ground bar in the breaker box.

I would go back to the building power supply, 1.) Verify the voltage difference between the common wire and ground wire. 2.) Drive a ground rod or check against a steel or copper water line,and and verify voltage between the common and ground rod and the ground wire and ground wire.

 

[deafwish]

I was simply using my truck as an earth point for the multimeter, as I couldn't use the concrete floor as an earth!
I get a tingle if the chargers are plugged in to the boat's shore power as well as if the chargers are plugged directly to the buildings power outlet.

 

[dratlief]

You will need to verify the voltage back to the power supply ground, it wouldn't hurt to isolate the chargers and check them separately to see if the issue is related to a single charger.

 

[deafwish]

Thanks for the responses.
I'll isolate each charger on Saturday & report back.
I was paranoid that if I have the boat in the water with the chargers connected, the current would dissolve my Bravo 3?!

 

[Grandad]

I think you may have discovered that there is "tingle voltage" between 2 ground points. This is a common phenomenon where there are more than one voltage sources connected to ground. The longer a ground wire is, the further it might be from the point at which it is connected to the earth. You can get a voltage potential that rises as the distance increases. This is a common problem in farms, particularly dairy farms where grounded milking machines have a different ground potential than a cow standing with wet feet on a wet conductive floor. It's often necessary to install a "tingle voltage filter" at such farms. Here's an Ontario government statement on this. Never swim at a marina. - Grandad
http://www.omafra.gov.on.ca/english/livestock/dairy/facts/09-075.htm