While we make our income dealing with the repair of boat wiring, I believe it is important to educate boat owners about marine electricity so that they are safe and their investment is protected.
I have seen some very scary jury-rigged wiring that literally looked like a rat’s nest and just so happened to have rat’s in there and wasps to boot! That’s scary stuff and also almost begging to cause a fire. So, let’s talk about parts of marine electrical systems.
I talked before about grounding and the difference between AC & DC. There is only 1 point where DC is grounded, at the battery. It is a free floating system where nothing is ever grounded to any metallic part of the vessel, most especially not the bonding system. It’s like a car sitting on rubber tires which provide insulation, the battery itself provides a negative potential.
These actually have nothing to do with electrical systems. Nothing should ever be grounded to bonding systems. Unskilled electricians often make the mistake of using this to ground electrical systems and this often ends in disastrous results.
Electrolysis & Galvanism
Boaters who don’t really understand electrolysis often abuse this work. Number one, all boats have electrical potential. All the metals on the boat have differing electrical potentials. This is exactly the principle that allows a dry cell battery to generate electricity. This electrical potential is called galvanism & is the reason why we put zincs on boats.
Now, electrolysis is stray current escaping and is most damaging. When this occurs, it eats up zincs quickly and leaves it looking bright & shiny. So, Shiny zincs = electrolysis & Dull eroded zincs = galvanism.
Shore Power Cords
The largest cause of issues w/ shore power systems comes from failure to maintain connectors on both the cord & boat connectors. Remember, these are exposed to water & will suffer from corrosion & general wear. This can eventually result in overheating & power drop. This alone can create conditions for fires & cause electrical equipment to work harder which reduces the life span of your boat. Maintain your shore power connections!
Coastie Marine recommend you buy only the highest quality power cords, as these will last longer and have the advantage of replaceable connector parts. Cheap connectors usually can’t be taken apart. Lastly: If you’re not turning off the dock breaker before disconnecting the power cord, start doing it! You risk getting electrocuted, but disconnecting an energized connector damages the contacts.
Thanks! Cliff Hairston, Owner/Marine Electrician