GI indicating a voltage

[tosher]

I recently lifted my boat for blacking and replacing anodes (old ones 75% worn). I also fitted a new Crowther prop, exactly the same size as the old one which is of unknown manufacture. When I returned to my marina berth and plugged into the shore power I noticed that the Aquafax galvanic isolator volt meter was registering a voltage. If I remove the shore lead no voltage is shown. With the lead unplugged I measured the voltage between the shore power socket earth pin and the boat plug earth pin and got 200mv. The GI voltage indicator always showed zero before I lifted out. No work at all was carried out to the boats wiring whilst ashore. What could be causing this and should I be worried?????

[blackrose]

When this happened on my GI it turned out that the house I take my supply from was using my boat as an earth path!

[NMEA]

I recently lifted my boat for blacking and replacing anodes (old ones 75% worn). I also fitted a new Crowther prop, exactly the same size as the old one which is of unknown manufacture. When I returned to my marina berth and plugged into the shore power I noticed that the Aquafax galvanic isolator volt meter was registering a voltage. If I remove the shore lead no voltage is shown. With the lead unplugged I measured the voltage between the shore power socket earth pin and the boat plug earth pin and got 200mv. The GI voltage indicator always showed zero before I lifted out. No work at all was carried out to the boats wiring whilst ashore. What could be causing this and should I be worried?????

 

Yes you should, have it checked by a qualified technician paying particular attention to the actual shore power and including vessels around you.

[jenlyn]

Try this, it may be of help

 

http://www.pkys.com/FAQ/galvanic.htm

[Keeping Up]

At least the GI is doing its job. At 200mV it won't be conducting any current.

[Gibbo]

What could be causing this and should I be worried?????

 

No major concern. It's below the conducting voltage of the GI so the GI is doing what it's designed to do and stopping any current. 0mV to 200mV is about normal for a steel boat in fresh water with magnesium anodes so you're just on the edge of normality.

 

The increase could be due to the new anodes. It depends which way round it is.