Hi Kevin,

Very interesting site.

I have a challenge. Switched my boat stove from Origo alcohol to a Kenyon single burner electric. My boat wiring had a spare breaker switch on the 120 volt panel and I decided to hook it up there.

I have to admit I am not very knowledgeable about marine electrical issues, so I paid very close to attention to how all the other 120 volt appliances (water heater, battery charger, etc) were wired and duplicated it. To my delight it worked.

However, at the time of connection I was using a normal extension cord with 30 amp adapters on both ends because the newly acquired boat didn’t come with a cordset. A couple of days later I went to West Marine and bought a 30 amp cable. When plugged in, I now have a reverse polarity light, and any and all 120v appliances trip the local and the main breaker.

Your thoughts would be very appreciated.

Shawn

Hi Shawn,

You may be dealing with an extremely dangerous problem, so either get professional assistance or use extreme caution.

I would say that some component in your shore power system has the black and white wires swapped. Or maybe the black and green.

Most reverse polarity lights are basically a light bulb between the white (normally neutral) and the green. If the white is accidentally wired to 115v, the light will turn on. If the green is accidentally wired to 115v, the light will also turn on, but all grounded items on your boat will be at 115v AC. This includes the engine and all metal thru hull fittings.

On 30 amp service, the “L” shaped terminal is the ground (green), the foot of the L points towards the neutral (white), and the last terminal is the hot (black).

I would use an ohm meter and test your new cordset to make sure the wires do not swap terminals inside. It is also possible that your old system has a reverse polarity item and a second item was wired backwards to solve the problem.

Again, please be careful.

Kevin

Hello,

First off…..Let me say, that I have enjoyed reading through a ton of posts on your site. You perform a great service, and knowledge is power.

I am going to be adding a trolling motor soon to my 191 CC Mako. The trolling motor is a 24 volt model. I would like to add two Group 31 deep cycle batteries for the trolling motor, and have one dual purpose battery to crank with. Three batteries total.

I would also like to pull 12 volt power leg out of my 24 volt series to power accessories and act as a house battery when I am not using the trolling motor, and an emergency crank battery.

I have included a wiring diagram that I drew up. Please take a look at it for me.

What concerns me most is the 12 volt ground coming off one of the batteries in series. Have I done this right? I thought this problem might be a good one to discuss on Easy Ac/Dc.

I have found no answer to this on the internet yet. I would be happy to update this diagram per your recommendations and give you the corrected one in the end, if you would like it.

Thanks,

David

Hi David,

Very nice schematic.

I would suggest some minor changes.

I would use battery A instead of battery B as your paralleling battery. Basically you would be paralleling to your 0 to 12 volt battery instead of your 12 to 24 volt battery. This will create a common ground in your boat wiring and help reduce stray current corrosion and accidental mis-connected grounds.

After you switch your paralleling switch to be connected to battery A, pay close attention to 12 volt devices that you may connect only to Battery B. If their ground wire comes in contact with any other ground wire in the system, it will create a dead shore across Battery A. You may want to consider installing circuit protection in the ground wire of any 12 volt item that you connect only to battery B.

Your bilge pump “manual on” switch needs to draw power from the same fuse as your bilge pump “auto” switch. You should only have a single source of power for any device. I would keep the switch at the helm, but run a wire from the auto bilge fuse (load side) to the line side of your bilge pump switch.

Make sure your wire sizes are appropriate. When your cranking battery switch is in the parallel or trolling motor battery position, the cranking circuit will include the wire from the switch to Battery A. Battery A to your Ground buss. Ground buss to Battery C. These wires should be at least the same size as the main engine battery cables.

Let me know if you have any other questions,

Kevin

Hi Kevin,

First of all, thank you for all of the time and effort that you put into your website. The boat wiring information that you share is invaluable.

So tell me Mr. Marine Electrical, do my ambitions exceed my abilities?

My wife and I have a small sailboat that we’ve enjoyed for many years. It’s a perfect size for the two of us and can’t imagine anything that would make the boat more fun…with one exception. We find that we are very jealous of our marina neighbors who have shore power. Whether they are using a television, a drink mixer, a vacuum, a toaster, or even a simple battery charger, we start down the “if only” path.

How tough a project is it to add AC power to an older boat? I’m reasonably comfortable with simple household wiring jobs, but have been told that marine AC can be an incredibly complicated and – if not done correctly – incredibly dangerous.

Any suggestions?

Thanks.

Matt

Hi Matt,

No project is too big, not project is too small when “Mr. Marine Electrical” is on the scene!

Seriously, there is a great new product from our partners at EzAcDc that will fit your needs. They have a complete marine shore power system that follows their snap-together philosophy of simplifying boat wiring jobs.

Installation of the new marine shore power system is easy.

The panel is pre-wired and comes with a remote outlet with 10′ of boat cable that simply plugs into a “snap together” plug on the back. The kit is also pre-wired with 10′ of Marine grade boat cable that runs from the boat AC panel to the included shore power inlet.

Best of all, any complex electrical connections are already made inside the powdercoated aluminum box.

All outlets are GFCI protected. And, for additional safety, the AC panel has a dual pole breaker to protect the boater if the dock outlet is wired backwards.

The panel also includes a power “on” indicator light and a reverse polarity light. It also comes with the AC to DC grounding wire that is required by the US Coast Guard. This wire runs from the back of the panel to your DC negative buss, engine ground, or battery negative and provides an additional safety path to ground if you have an AC fault on your boat. Even though required, this wire is redundant on this well-designed system since the GFCI also protects everything.

Additionally, there is a single outlet on the back of the shore power panel to allow a built in AC device to be connected. This is ideal for a battery charger or refrigerator that comes with a standard 15 A household plug. Simply plug it into the back of the panel before installing.

It comes with the industry standard 30 amp Marinco inlet. You can choose between the standard square plastic inlet or upgrade to the stainless steel version. Both will connect to an 30 amp marine cordset or adaptor.

Please let me know how your project turns out. I always like pictures.

Kevin

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

Dear Ron,

Your problem was common with boat restoration projects – until the introduction of Harness in a Can.

Harness in a Can lets you spray pro-quality boat wiring into even the most hard to reach areas. Simply point, spray, and apply power. What could be easier?

And, it’s not just easy, it’s ABYC approved! Harness in a Can sprays out a harness with correct wire color and sizing – and with all of the connections that you need to get the job done fast.

If you order now, you will also receive a cap snaffler – absolutely free. Cap snafflers snaffle caps off any size jug, bottle or jar…and they really really work.

Call now to order. The toll free number is 877-277-3665. Operators are standing by. That’s 877-APR-FOOL.

Kevin.