Hi Kevin

I am working on a boat’s AC shore power system, trying to install a galvanic isolator.

Unfortunately, the previous owner did not use the standard boat wiring colors.

I am trying to determine which wire is the ground and which is the neutral. I know I get current between the hot and neutral and the hot and the ground and none between the neutral and ground. But how do I tell the neutral from the ground?

Thanks,

Hank

Hi Hank,

If your marine wiring is correct, the neutral and ground should not be connected together.

The neutral and hot wires will be connected to the dual pole main breaker. The ground will not.

If the original owner tied the neutral and ground together on the boat, the GI will do nothing.

Please let me know if you need more info,

Kevin

Kevin,

I’m in the midst of building a small submersible ROV with a 200 ft tether, so I can see what’s under the waves as well as above.

I’m considering three power solutions for the ROV, on-board batteries (last resort), power in tether at 48 volt DC, or power in tether at 110 volt AC. It’s about the last two options that I have some boat wiring questions.

My idea with 110 volt AC is to get a 400-500 watt inverter, plug it into the DC port in my cockpit, and use an AC-DC converter in the ROV to get 12 volt power, hopefully about 10 amps. I want to run two-wire conductor between the inverter and the ROV because it weighs one third less than three-wire and I want to minimize the weight bulkiness of the tether the ROV will be towing around.

Alternatively, I could get a step-up converter to go from the cockpit’s 12 volt to 48 volt, then step-down from 48 volt to 12 volt on the ROV. A 200 foot 12 volt tether would be way too bulky.

I’m concerned about several things.

1. Are there any glaring safety issues with these during normal operations?
2.  Assuming I am going to eventually get a short, what are the risks I could face and what precautions should I take in anticipation?
3. Am I opening myself up to some kind of galvanic action disaster?

Thank you,

Orrin

Hi Orrin,

I would set up your boat wiring with the 110 volt version.

Run the ROV through a GFCI. If your two conductor wire has a shield, connect it to the case ground on the ROV and to your AC ground. Any AC fault will trip the GFCI long before the risk of an AC shock.

Please send pictures when you project is complete,

Kevin

Kevin,

My 1990 Sea Ray Express has two 454 Mercruisers.

I have no voltage feed to my starboard alternator. The large red wire goes to the battery isolator,but I believe the alternator is powered up by a smaller red purple wire. Where does it come from? It has no voltage on it.

Any help is welcomed and gratefully accepted.

Bob

Hi Bob,

On a marine engine, if an alternator has an external excite wire, it is usually purple and is basically keyed ignition power. When ignition power is supplied to this wire, the alternator basically turns on. This type of alternator works better with a battery isolator because you are actually sensing the battery voltage and not the alternator output voltage.

If your alternator is self exciting and internally sensing, then the single red/purple wire is the “idiot light” wire. This wire goes to ground when the alternator dies. It is connected in series with an indicator light. IMPORTANT: If you apply ignition power directly to this post on this type of alternator, you will burn up the internal rectifier.

Determine which type of alternators are on your boat using an internet search and the model number on them. If they are self exciting and internally sensing, your alternator is dead. If they have an external sense wire, trace down the red/purple wire and determine where it is not making connection to the ignition wire.

Happy boating,

Kevin