Melting AC

Hi Kevin

I purchased an old 1989 cruiser, a Regal 280 Commodore, and tripped the 20 amp dockside breaker while using a hatch a/c unit and an electric kettle. I have 30 amp service in the boat.

I reset the breaker and then the AC electric system worked for a few minutes and then went dead. Neither the dockside breaker nor onboard breaker tripped, but we smelled a burning smell. I immediately unplugged the AC system and looked behind the AC panel.

At the main breaker switch where the shore power comes in, I found the white wires melted and melting damage to the black wires. I can fix all the wires, but there is also some sort of capacitor that was wired as a jumper between the green and white wires and it is not in the wiring diagram of the boat. It looks like it has been burned out. I want to know what to replace it with, and then if this overall problem is something that points to the result of another problem or if it may have been some old wires getting warm and then touching.

I can replace everything as it was once I know what to put between the black and green wires, but don’t want to do that and then plug it in if there may be other issues that need addressing.

Thanks for your help.


The only connection in your panel between the neutral and ground would be a reverse polarity indicator. Instead of a light, some boats have an alarm. Some of the piezoelectric alarms look like capacitors.

Hope this helps


Wiring a Boat’s Carbon Monoxide Detector

Hi Kevin,

Could you please briefly outline location of carbon monoxide detector on a cruiser? Do I have to dedicate a unique circuit to the monitor.

My boat has two state rooms so I assume two monitors are required. My current plan is to wire directly to bus bar coming off battery and not to main electrical panel.



Hi Sanford

I would refer to the CO monitor’s installation manual or the manufacturer’s website for the best location.

  • Size the wire for 3 percent voltage drop but do not use wire smaller than 16 awg.
  • Use circuit protection at the source of power.
  • If you are using a breaker, I like to use a push to reset style for co monitors instead of a rocker style to make it more difficult to turn off.

I also prefer to wire CO monitors and bilge pumps to have constant power and not be controlled through a battery switch, but sometimes it is not possible to accomplish this.

Hope this helps,

Ground Charge?


I need your help with a marine electrical shore power question.

My boat is plugged into dockside power and there is a 100 millivolt charge on the green ground wire. I have checked with the marina and they have checked their system which is in perfect conformity to the rules.

There is no indication of this on the shore power plug but it appears when you put a meter to the boat which is in the water and seems to make a ground through the water.

What is the reason for this?



Hi Ray,

How are you measuring the 100 mV?

Is it on the shore power plug before you connect it to your boat or is it on your boat when you compare the green to the white?



It was measured on the boat.



The 100 mV difference is simple to explain.

When current passes down neutral wire there is a slight voltage drop. Voltage = Resistance x current. Since there is no current passing down the ground wire, there is no voltage drop on it.

Your dock box is tied in with several other dock boxes with the same neutral and ground wires. If every boat was disconnected from the system, you would not see the 100 mV difference. At times, it is possible to see voltages higher than 100 mV.

Hope this helps,


GFI Trips Common?

Hi Kevin,

I trailer my boat but when it’s in the driveway – or at a marina with household GFI 3 prong plugs – I will use an 30 amp to 15 amp adapter to plug shore power into home to charge batteries, etc. (Not the A/C).

My problem is when I do that and plug it into any GFI outlet, it trips the GFI protector. It doesn’t when I plug into non-GFI outlet. And it works fine at marinas with normal 30 amp shore power outlet.

I understand the GFI detects small inequalities of the inflow current vs. the outflow current. Is there something wrong with the boat wiring like a short cicuit? Or is this common with boats?


Hi Steve,

It is common for boats.

To help reduce marine electrical system noise, some older AC components have a connection between the AC neutral and the AC ground internally. This worked great for noise, but will trip most GFCI outlets.

The culprit is either your battery charger or the AC/DC converter for a refrigerator. You can either replace the components on the boat and hope you solve the problem or just plug it into a non-GFCI outlet.

Hope this helps,