timskip
New Member
Does anybody know if the alternative to fitting a galvanic isolator to a steel boat moored in fresh water and hooked up to shore power is to run a good earth wire directly to an earth spike?
Galvanic isolation, the alternative?
- Thread starter timskip
- Start date
Sandyman
Well-Known Member
No its not an alternative. It would in fact increase the process of galvanic action.
A galvanic isolator actually goes in the earth line betwix boat & shore supply earth.
A galvanic isolator actually goes in the earth line betwix boat & shore supply earth.
Rivers & creeks
Well-Known Member
I found this video really helpful http://www.youtube.com/watch?v=vGehTCw_voI
rogerthebodger
Well-Known Member
No but an isolation transformer would be and some say better.
Gumpy
Well-Known Member
You have two choices
Isolation transformer
Galvanic isolator.
Any other ideas like earth stake connection removing the ground from the cable etc will either make corosion worse or be dangerous.
There is good info on the smartgauge website
http://smartgauge.co.uk/galv2.html
Isolation transformer
Galvanic isolator.
Any other ideas like earth stake connection removing the ground from the cable etc will either make corosion worse or be dangerous.
There is good info on the smartgauge website
http://smartgauge.co.uk/galv2.html
claudio
Well-Known Member
A good article, carry on reading to http://smartgauge.co.uk/galv_tran_02.html before making up your mind if the the GI is of any use to you at all
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Gumpy
Well-Known Member
I am very aware of just what problems emc caps can cause one of the reasons I would never use a GI in freshwater.
theguvnor
Well-Known Member
maby
Well-Known Member
Exactly - the water you are floating in is already a pretty good earth - and that's the problem - the mains earth coming in on your shore power is often quite long and not as good an earth as the water is - it's that discrepancy between the mains earth and the earth path through the water that is responsible for the erosion of your anodes.
VicS
Well-Known Member
So you are suggesting that the water is a better earth than the earth conductor in the shorepower supply.
Would it therefore be better to simply use the anodes, skin fittings, stern gear or, in the case of a metal hull, the hull itself as the earth and not connect the shorepower earth to anything at all?
That does not seem to agree with expert advice or standards such as ISO 13297
maby
Well-Known Member
I don't think "better" is the right description - "more accurate" might be. Think about the purpose of the earth wire in a mains supply - it's there to protect you against getting electrocuted in the event of a short circuit in a piece of equipment. To do that, it simply needs to be within a few volts of the potential of the ground you are standing on and the water pipes etc. dotted around your kitchen/bathroom/living room. But it does need to be able to carry a high current - upwards of a thousand amps - at least briefly, until the fuse or circuit breaker has blown and disconnected the supply.
The earth pin in your 13a socket is connected back to an earth stake or ground plane (possibly a water pipe). The wiring will have some resistance and will be running close to other wiring, possibly picking up an induced voltage. In the marina with shorepower sockets on pontoons, the cable run back to the distribution panel may be quite long and will be shared with other boats on the same pontoon - any earth leakage in their electrical installation may push the shared earth wire a fraction of a volt above true earth potential.
The water around your boat - and the metal components in contact with it - will be at true earth potential, but the resistance to ground will be high - salt water is not a very good conductor. The fraction of a volt difference in potential between the sea water and the shorepower earth connection is what causes the anode erosion, but the water would not be able to carry the current necessary to protect you from shock or to trip out the circuit breaker.
