Electrical Question re shore power and galvanic corrosion

The galvanic isolator prevents DC from riding the shore ground conductor and dissolving someone elses boat too. An isolation tranformer separates the shore power ground from the vessel's ground and is more a safety device to reduce the chance of electrocution.

If there was an AC ground fault on a utility referenced system with a less than perfect ground, a person touching the shore or swimming alongside (worse in fresh water) could be electrocuted since the marina or the world provides the other side of the circuit. With an isolation transformer, the circuit is not referenced to the world or the marina ground system and nobody gets hurt.

Galvanic isolators, properly installed, will block the majority of DC curent from the ground wire in the shore cable.

An isolation transformer will block 100% of the DC current and you do not have a physical ground connection to the dock system. Some transformer models will also "boost" the AC shore voltage if it is low which can help in outlying areas with substandard dock wiring/power levels.

Neither system will eliminate the need for proper bonding and zincs though! Problems with the DC side of the boat can still give trouble and should be checked regularly by someone with a corrosion test meter regardless of the system installed.

New ABYC rules are mandating the installation of an ELCI (Equipment Leakage Current Interrupter) circuit breaker in the shore inlet wiring. These are also known as Ground Fault Interrupters and while they are not as sensitive as the ones you see in your house's bathrooms, they will add a degree of safety for the whole boat and are highly recommended if you are doing any major revamping of the boats wiring. They are just now becomming available from the major panel manufacturers.

Despite the ABYC recommendations for ground fault interrupters I don't recommend them for older boats. Our boat had 40 years of accumulation of salt spray some of which found its way to the electrical wiring. The leakage was minuscule but enough to trip the GFI in damp weather.

If you google Galvanic Isolator you will find them from about $99 up to $299 and some excellent technical information. You don't really need one with all the bells and whistles, they are extremely reliable.

Hi,

Maybe at 40 yrs old the GFI on your boat was past it's service life?

Was this on the Shore Power or in the head of your boat?

Also, Would the fact that you feature Galvanic Isolators on your website be any reason why you are against the ABYC Recommendations?

No the GFI were added in 1989, the boat was made in 1960. We had the problem with two GFIs, one on the salt water fire pump and one on the outlets in the galley. We did use domestic GFIs. I understand that you can now get less sensitive GFIs for exactly the problem we encountered.

I'm not against the ABYC GFI suggestions, I'm just alerting users to a potential problem we encountered. The GFI should not be confused with a Galvanic Isolator, they are entirely different items. A GFI will do nothing to prevent galvanic electrolysis.

Please also be aware that galvanic currents can enter your boat via telephone lines and cable TV wires. Sneaky SOB's.

Household GFI outlets only seem to last about 6 months in the marine environment. The Hubbel ones work well and last much longer

The ELCI ground fault protection Bill106 refers to is whole boat protection and trips at a substantially higher current than the type used for convenience outlets. It should not trip at nuisance leakage levels.

I use a grouper zinc fish that i hang on the stern of my striker.Its a fish that's made of of zinc connected to a wire with a battery clamp at the end that's connected to a good ground on the boat.Any stray electric current in the water at the dock goes directly to the zinc fish.Just remember to pull the fish up before you go anywhere.The fish i have now has lasted 5 years in salt water.A small price to pay for no corrosion on your boat,zincs,shafts,props,hull,boat lift,etc.

Unless that fish is attached to your grounding system you'd have the same effect by dumping some old zincs in the water around your slip. BTW, you don't want zincs to last. If they do you're either in a marina without issues or they're not doing their job.