Electric shock from water heater ?

[Trilogy]

I've just installed a 1KW 240V immersion heater in my existing hot water tank. It's wired directly to the yachts original mains panel which has a dedicated water heater switch (It's a Westerly Ocean 33). I've tested the earth connection from the tank to the mains outlet...0.00 Ohms.


The boat is out of the water. When fitting a new anode on the sail drive, I noticed a mild tingling when touching the sail drive. I noticed the same tingling when touching the cabin heater exhaust port.

The tingling stops when the water heater is turned off.

Both the RCDs on the boat and the marina supply are usually very sensitive but neither have tripped.

Any ideas what's going on ?

Thanks,

 

[savageseadog]

It's a small amount of current due to the fact that mains earth is not the same as ground, there is a voltage difference. The current isn't enough to trip the breaker.

 

[earlybird]

Suggest that you have a leakage from somewhere in mains supply that is below the RCD trip threshhold of several 10's of mA. Metal items connected by, say, boat wiring are transmitting it. It sounds potentially, (pardon the pun ), hazardous to me and should be traced as a matter of urgency.

 

[John100156]

I reckon Savageseadog has it. Its not unusual for resistive immersion heating elements to leak very small current flow into the water system hence earth. Often the cause of RCD trips as heating elements fail.

If practical/possible you could try earthing all conductive paths together to include cylinder (equipotential bonding) which should erradicate it. You could try a temporary bond to start with! /forums/images/graemlins/cool.gif

 

[savageseadog]

I was assuming that your mains earth was bonded to your engine/battery negative. I also assumed that your appliances were bonded to earth, correctly.

 

[Solent sailer]

i think the previas are probable correct, i recomend you find a frendly electrician and borrow an insulation tester to check the immersion heater, test the immersion heater with the rest of the boat isolated ( test at 500Volts and you should get a reading of over 2Mohms idealy over the range of the meter with a modern meter this will be in the reagon of 2000Mohms). you need an insulation resistor with the 500v output not a multymeter you wont get the seme results testing at 6volts.
The tingeling is probable an indication that the heater is starting to break down, it wont be doing any of your underwater metalwork any good!!

 

[Trilogy]

Thanks all for your thoughts.

The mains earth does not appear to be connected to the negative side of the battery. On the engine (Volvo 2020) there is a yellow sticker with the earth symbol and a red line through it which I took to mean do not earth.

Any thoughts ?

 

[bigwow]

I had a similar problem last year, it turned out to be an earth leakage from the magnetron in the microwave. /forums/images/graemlins/blush.gif

 

[Solent sailer]

i wouldent expect to see the earth directly connected to the boat "earth" as this could have an adverse effect on your anodes (and any other metalwork), the earth would be connected through a galvanic isolator to prevent a direct electrical contact. or as in your case isolated from the boat "earth" and just earthing the 230volt items with there own earths.