Hello Kevin,

My question is regarding marine wiring.

On my marine electrical, I’m using an isolation transformer in order to transform 220V to 110V.

Recently, the boat’s reverse polarity indication light is on. I’ve opened the circuit to see how this indication is measured and saw that there is a diode and led connected between the neutral and the ground.

I’ve realized that in the current situation the output of the transformer is basically floating, therefore the neutral line can have any voltage. One of the solution that I’ve seen online is connecting the neutral line at the output of the transformer to the boat’s ground (that is not connected to the shore’s ground). So I have several questions about it:

1. Is there advantage in connecting the neutral to the boat’s ground over working with floating voltage?
2. Is it ok to make this connection?
3. For about a year, the indication was off, what can be the cause for it to be on now?

Thanks in advance,

Ilia

Hi Ilia,

At the source of power, the neutral must be connected to the ground. With an isolation transformer, this is on the output (boat size). Please connect the output neutral and ground together immediately. It is an extreme shock hazzard as is.

The reverse polarity indicator is connected to the input side of your transformer. With an isolator transformer, the light is more of a nuisance than a concern. It is telling you that the polarity is reversed (Neutral is hot) on the input. Since you have an isolation transformer, you really don’t care as long as the neutral and ground are connected together on the output side.

Hope this helps,

Kevin

Hi Kevin

I’m working on a 32 foot cruiser. I’ve rewired the whole boat and can’t get the DC side of the panel to work “lights or anything”.

I was wondering if the generator has to be on? Also shore power #2 isn’t working, #1 works fine and will run the AC side of the panel.

I’m stumped on the DC side though, it is strange to me if it’s not the generator. I’m kind of lost if you could please help? I need some.

Thanks,

Barry

Hi Barry,

Marine electrical DC power should have nothing to do with the generator.

Using a meter, start at the source of power, the battery, and make your way to the DC panel to find the problem. It is probably a bad ground connection or loose circuit breaker wire that is causing the problem with the boat wiring.

If you are not experienced with marine AC wiring, I would hire an electrician. It is easy to make a fatal mistake and then you wouldn’t be able to write back and tell me what was wrong…

Looking forward to hearing from you!

Kevin

Hello Kevin,

I am really impressed by the Easy Add AC Shore Power System that you designed for your partner boat wiring site.

But, before I purchase the AC system, I have a couple of questions.

If my battery charger is mounted on the transom can I run 12 gauge marine three wire to the plug on back of panel and put a regular three prong plug on it? Marine grade of course. I did not want to run an outlet to the engine compartment.

Also could you please explain the placement of a galvanic isolator in the main line?

Finally, do you have any suggestions for marine grade three prong plug?

Thank You,

Morris

Hi Morris,

I am not fond of outlets in the engine room either. Even though it would be protected by the GFCI, you still have no idea if a non-ignition protected device will be plugged into the receptacle.

I would consider a studded battery charger as compared to a charger with pre-installed leads. You can run your 12/3 from the charger, up to the panel, and install a normal three prong plug at panel end. There is no need for it to be marine grade when it is in the cabinet in cabin. If this is not a possibility, I would make the charger AC connection outside the engine room.

Galvanic isolators are installed in the green grounding wire between the AC inlet and the marine electrical shore power panel.

• Cut back the white insulation.
• Cut the green wire.
• Install ring terminals on each end of the cut green wire.
• Connect them to the galvanic isolator.

Hope this helps,

Kevin