electrical problems on narrowboats

What’s the difference between Earth Leakage, Stray Currents and Galvanic Currents?

Earth Leakage is mains electric current that flows to earth from the 240v mains circuit in your boat due to electrical faults in it’s wiring or equipment.

buy earth leakage tester for narrowboatIt’s potentially lethal, but fortunately we are protected from excessive earth leakage by RCD’s, sometimes called the Earth Leakage Circuit Breakers. Every boat and every shore supply should be fitted with an RCD, and in the event of a fault in the boat’s wiring or equipment, the RCD disconnects the electrical supply for the sake of safety.

What Earth Leakage does NOT do – at least not directly – is cause corrosion to your boat’s hull.

However, there are other types of earth currents that DO damage a boat’s hull and deplete it’s anodes.

anodes wasting away quicklyGalvanic Currents flow whenever your boat is connected to a shore based electricity supply. They occur as a result of chemical reactions between the metalwork of a boat and surrounding metalwork such as pontoons, other boats, and the minerals in the bank side.


Galvanic currents are at a very low voltage, so they’re not dangerous to life. But they DO cause corrosion of a boat’s hull, and faster than normal anode use. Using a Galvanic Isolator or isolation transformer can prevent this from happening.

how to prevent damage from stray currentsStray Currents are currents that flow as a result of faulty wiring or equipment. Unlike Earth Leakage, which would “trip” the RCD, Stray Currents often show no symptoms, and everything appears to be completely normal. But it’s not.

These voltages are not high enough to kill, but they are MUCH higher than Galvanic Voltages, so the potential for causing hull damage is enormous. Anodes can corrode from new to nothing in a matter of months. When, or even before, the anodes are gone, the boat’s hull corrodes. Our latest generation of Galvanic Isolators have been designed to warn you of Stray Currents so that you can act quickly to prevent hull damage.

phone charger power supply danger to boats hullImprinted Leakage. There is yet another type of leakage, known as Imprinted Leakage. Imprinted leakage can come from the power supplies of battery chargers, computer power supplies, phone chargers etc. Even BRAND NEW equipment can cause imprinted leakage.

Because of the high frequencies that these devices use, some of their power can be “coupled” into the boat’s wiring, and then to earth. There is often a DC (direct current) component to this type of leakage, and it’s this DC component that can cause rapid damage to your boat’s hull & anodes. Again, everything can appear normal – this type of fault will NOT trip an RCD.

Our latest Galvanic Isolators can detect this (and all other types) of leakage. We also market an Earth Leakage Tester which can be used to check for ALL the above types of earth leakage.

prevent electric shocks on boats

zinc saver wire in type with status monitor


zinc saver galvanic isolator for narrowboats and widebeams