Dear Kevin,

I am currently beginning my first boat wiring project, a total rewire of a small Owens cruiser from the late ’60s.

Here’s my problem:

The old wiring runs behind the original paneling and headliner. I could try dismantling everything to remove and replace the wires, but am concerned about damaging any of the woodwork. It’s old. It’s gorgeous. It would be a bitch to replace.

I don’t mind leaving the old wiring in place and just running a new harness, but that still leaves the problem of installing the new wires without causing any damage.

Any ideas?

RP

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Kevin.

Kevin,

With no generator or selector switch, my boat’s galvanic isolator is currently located between the shore power ground connection and the 110V ground bus. The 110V ground bus ties into the 12V negative bus and the boat ground (a steel pontoon).

I have recently restored my onboard generator and have installed a source selector switch (shore power or generator). I’ve read everything I can and I still can not identify to my satisfaction how to connect a galvanic isolator into an electrical system with shore power, an onboard generator, and a source selector switch.

The confusion (on my part) is that the battery selector switch being used has a separate connection for the ground wire from each source on what appears to be a solid bus bar connecting them. This suggests that both the shore power ground and the generator ground are connected and wired to the isolator inlet and the isolator outlet is wired to the 110V ground bus, the 12V negative bus, and the boat ground (steel pontoon).

Is this correct? Maybe the separate ground connections to the battery switch exist only to support the reverse polarity LED light, but it is still confusing.

Your guidance is requested.

Dave Freeman
Richland, WA

Dave,

The main reason for a galvanic isolator is to prevent stray current corrosion through your boat’s shore power connection. It basically induces enough of a voltage drop to prevent a galvanic cell from being created between your metal underwater gear that is electrically connected through your shore power ground wire to other metal gear in the same body of water – usually the dock.

To be effective, the galvanic isolator must break the shore power ground wire – the green wire between your inlet and your AC panel. All of the AC grounds on your boat wiring system should be connected together – Generator and existing AC systems.

You should have a single wire that connects the DC ground to your AC ground.

Hope this helps,

Kevin

Kevin.

Can you tell me the correct boat wiring for a galvanic isolator into an inverter/charger? Everyone in the marina has their own opinion, I just need a pro’s advice.

I need to know if the green from the shore power goes into the inverter and then to the 110 volt panel. Then does it go from the panel to the battery and then the engine block?

Thanks.

John

John,

The green wire goes from the shore power inlet to the galvanic isolator. From the isolator, the green wire goes to your inverter which is connected to the AC ground on your distribution panel. There should also be a wire between the AC ground and the DC ground (engine block)

Have a great day,

Kevin

Hello,

Please could you comment on the boat wiring diagram that I’ve drawn up.

It includes:

• Twin Verado outboards
• Shorepower
• Generator
• House batteries.

I’m currently trying to wire up a new boat here in Oman (no technical expertise available) and I’m really concerned about dangerous AC currents floating around the boat whilst my family swims.

Please could you have a look and give me your comments as I’m no expert at this?

I know that I’m missing an earth wire from the fused junction!

Any input from yourself will be most welcome.

Kind regards

Glyn

Hi Glyn,

Very nice diagram!

I have a few comments.

• Add circuit protection at the source of power for your 24 hour emergency bilge pumps fuse panel.
• Add circuit protection at the battery switch for your main DC distribution panel
• Your shore power ground (green) needs to run to your AC ground buss
• Your galvanic isolator is connected between your shore power inlet and the AC ground buss in the green wire

Also, I would consider not connecting the 3 bank inverter to all 3 banks. Instead,

1. Connect two legs to the house battery bank
2. Connect one leg to the port engine battery bank
3. Connect 0 legs to the starboard engine battery bank

This would allow you to completely drain your dc system with the inverter and still be able to start your starboard engine and charge the system through your automatic charge relay

As drawn, your boat’s AC electrical system should be shock proof.

Most marine AC problems occur when the DC ground is not connected to the AC ground. If you boat has an AC fault to a DC component, the common ground will allow the circuit protection on your AC distribution panel to trip and not energize the water below.

Please send me pictures of this project,

Kevin

Hello Kevin,

Thanks for your input.  I’ve updated the pdf (in case you want to use it)

I’ll take pics and send them to you. But, it might take a while as I’m in Oman and it’s a real struggle to source the various electrical components. Nevermind the marine grade wiring (at the local marina they have a bad habit of using domestic grade wiring).

That’s why I’ve elected to attempt all this myself.

Regards

Glyn