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Galvonic Isolator - Ac Leak

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Morning All,

The broom is having it's weekly strop.. She's still out the water but I noticed last night that we have 2 warning lights on the shoreline galvonic isolator indicting we have an AC leak..The lights are very weak.. Do we have an issue here? do we need to rewire the 240v system before putting into the drink.. if we want to debug it where on earth do we start? 

cheers Alan                     

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Alan, Hi.

Here's what Safeshore say:

The models Gi70 & Gi100 are standard isolators & will control all dc galvanic problems below 1.2 volts. (Most galvanic currents are below 1.2 volts). The models GI 70sm /smi & GI 100 smi are advanced isolators with fault indicators. They control all galvanic problems up to 2.4 volts thus offering extra protection .The status monitoring indicates and identifies fault conditions & allows easy testing of the galvanic installation . All models offer protection against both “Galvanic” & “Stray” currents. What is the difference between “Galvanic” & “Stray” current? Galvanic currents are currents set up due to differing voltage potentials present on metals such as props / shafts/ anodes / skin fittings etc between boats /pontoons etc They are the currents which flow from boat to boat or from boat to pontoons etc. The current flow increases rapidly when you connect to shore power. Stray currents are highly destructive currents which flow from leaky shore power supplies /defective a.c. or d.c. wiring, leaky bilge switches etc resulting in increased voltages finding their way to the metalware of your boat: This is a far more serious & destructive current than pure galvanic current & is the one that does serious damage in very short periods of time . Our status monitor models Gi 70sm / Gi70smi /Gi 100smi gives advanced protection levels & inform you of the type of leakage thus saving serious damage! What does the remote monitor do? The status monitor constantly watches for any current flowing through the "green" earth wire. If a fault occurs a warning led indicates fault

Why does the monitor have 2 L.e.d's? (light emitting diodes : infinite life & far more reliable than conventional bulbs) The monitor indicates both d.c. leakage (indicating a fault on board the vessel) & a.c. mains leakage (indicating faulty shorepower or defective vessel mains leakage condition) One l.e.d .illuminates when d.c. fault condition is present : Both l.e.d’s will illuminate when A.C. fault conditions exist.

I have 2 mains inlet sockets on board the boat : Do I need 2 isolators? Not necessarily ; If the 2 earth wires are bonded together then 1 isolator is sufficient. If the supplies are designed to be individually earthed then 2 isolators are recommended. We supply excellent installation instructions & wiring diagrams with every isolator.

How can I test the isolator? : Do I need to disconnect it to test? You do not need to disconnect to test. Simply check the isolator with a digital meter on diode check scale : The readings should be approximately the same in both directions. We supply full instructions for installation & testing all isolators. They can be fitted easily by competent d.i.y. persons We also have a helpline which does just that! A word of warning however! Some budget digital meters have an internal battery of 1.5 volts . These meters are unable to give accurate readings when testing galvanic isolators . Meters containing 9 volt internal batteries have the ability to “turn on “ the internal diodes of the isolator & give accurate, reliable reading

We have a Streling Isolator:


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Thanks again John.. Your "competent" comment brought a smile to my face.. (Competent.. + Medway towns.. :party::) :swordpir:


I emailed Safeshore .. and Vic kindly replied with the following.., which makes sense as our battery charger in here is massive (and new and just under where this isolator is)..:


Thank you for email. A feint glow of the both led,s is usually indicative of the prescence

of small interference pulses on the earth line. These pulses are generated from appliances

such as battery chargers, microwaves, computer power supplies, aircon units and invertors.

The status monitors are extremely sensitive and are able to sense these pulses creating a

slight glow. The source may be on your boat or a neighbouring boat (You can sometimes

eliminate your neighbouring boats by discretely unplugging them from the shore power whilst

monitoring the led,s!). To further locate the source you can unplug appliances on your own

vessel whilst monitoring the led,s. Occasionally these pulses are transmitted via the shore

power pedestal itself and may indicate a very low level a.c. leakage on the marina shore

power system. Either way the slight glow is usually of little concern as the current involved is

minimal and the isolator continues to block effectively.

All destructive galvanic currents are D.C. generated so a fully illuminated single

led would require further investigation. I attach a further explanatory letter to this document.

Hope this explains..

Kind regards,

Vic ....... Safeshore Marine


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If that was in a house it would be an earth fault leakage, Alan. When I worked on coastal coal and timber boats that had three pygmy lamps down in the engine room power board, if one was dimming you could bet it was a poor wire connection. I hope you resolve the problem quickly. As the Admiral says, a Meggar Tester may help find the fault.


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