DC Power Distribution Updating

Electrical and electronic topics for small boats
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

DC Power Distribution Updating

Postby jimh » Sat Mar 24, 2018 1:49 pm

To successfully update the 12-Volt DC power distribution on a small boat, you need:

  • basic hand tools used to work with electrical wire, cables, connectors, and so on
  • some skill in using those tools
  • marine-grade wire of the proper wire gauge and proper wire insulation color on hand
  • a good secondary power distribution panel installed.

With these attributes, the re-wiring the basic 12-Volt DC secondary power distribution should not be particularly difficult. I overhauled the electrical power distribution at the helm station on my 1990 Boston Whaler and described the process in a short article with illustrations and further links. See


The project was not difficult for me, but I should mention that I have been performing this sort of wiring since I was about age 10, or for more than 55-years.

The most important aspect of any re-wiring: make a careful and detailed sketch of ALL the existing wiring before you remove any of it. Take digital photographs showing details to use as reminders and references.

Before beginning my project I ordered several lengths of 16-AWG marine-grade wire from GENUINEDEALZ.COM. I ordered 100-foot spools of RED and YELLOW wire for 12-Volt DC power wiring, and 50-foot lengths of 16-AWG in BLUE, BROWN, GRAY, and VIOLET insulation for wiring of branch circuits.

I also ordered an assortment of ATC fuses in various Ampere ratings. When you buy a Blue Sea Systems distribution panel, the fuses are not included. Order plenty of fuses; you will need two spares for each value. Also, I found I was running out of NEGATIVE bus terminals before I ran out of POSITIVE circuits. Order the 12-circuit panel, even if you think you won't ever make use of all the circuits.

When the project is finished, memorialize the wiring with a good sketch of the power distribution panel showing what device is connected to each circuit, the fuse rating, the wire color, and any identifying markings on the wire.

My approach to wiring concentrates of functionality over art-object appearance:


Working on the inside of a helm station can be very awkward. Take your time and get some cushions and pads to lay or sit on. At the factory much of the wiring is pre-assembled outside the boat. Working in the confined access that usually occurs on the boat will be difficult.

Avoid having to install butt-splice connectors to extend a wire's length as much as possible. Choose the location for installation of the new secondary power distribution panel so as to avoid having to lengthen all the wiring. Check circuits already in place for splices, and replace the wiring to eliminate any splices found. I found the circuit for the white all-round lamp at the stern had been spliced in three places, a total of six butt-splice connectors. I tore out that wiring and replaced it with new wiring.

Above I mentioned that I ordered marine grade 16-AWG wire with insulation colors of RED, YELLOW, BLUE, BROWN, GRAY, and VIOLET. There is a general practice in marine wiring to employ wire with different color insulation to aid in identification of the function of the circuit. I have compiled a comprehensive list of wire insulation color codes in an article I wrote for the REFERENCE section. See

Marine Wiring Color Codes

In the case of the six colors of wire insulation mentioned above, I used them as follows in my re-wiring project:

  • RED = 12-Volt positive circuits from secondary distribution panel individual fused circuits
  • YELLOW = 12-Volt negative circuits from secondary distribution panel negative bus
  • VIOLET = switched 12-Volt positive, usually associated with the engine ACCY ciruit
  • BLUE = instrumentation lighting or general lighting circuits
  • BROWN = pumps, sensor, or sender circuits
  • GRAY = navigation lighting circuits

The use of YELLOW for the 12-Volt negative circuits instead of the traditional BLACK is now done to disambiguate the DC wiring on the boat from any AC wiring, which uses BLACK as the HOT conductor. If you don't anticipate ever having any AC wiring on your boat, you could continue to use BLACK as the insulation color for the 12-Volt negative circuit.

Note that in older Boston Whaler boats with cabin lamps, those circuits use GRAY insulation wire.

To retain wiring, use cable clamps. Although one often sees metal cable clamps with rubber cushioning used to hold electrical cables, for small diameter (16-AWG) wiring I prefer to use nylon cable clamps.

Nylon Cable Clamps

Metal Cable Clamps with Insulator

As I mentioned earlier, I ordered wire and other components from GENUINEDEALZ.COM. I found they were a good supplier, had excellent prices, and delivered quality material.

If you plan to re-wire any primary battery connections, you should consider ordering the primary wiring with pre-installed terminals. Most boaters do have the proper crimping tools to crimp terminals onto large conductors. Unless you want to buy an expensive hydraulically operated crimping tool, I recommend buying pre-made cables cut to length with terminals already installed. Just be careful to specify the proper stud size, wire size, and length.

If you have a VHF Marine Band radio, I recommend you read my article

VHF Marine Band Radio Installation on a Small Boat
http://continuouswave.com/whaler/refere ... ation.html

The article summarizes many aspects of radio installation an points to further explanatory articles on a number of topics.

All wiring that is to be terminated under a binding post should be fitted with an INSULATED RING TERMINAL connector. The connector should be properly crimped to the wire. I am old-school and also usually solder the wire to the terminal connector after crimping. When selecting RING TERMINAL connectors there are two dimensions to consider:

  • the gauge of the wire to be connected to the connector
  • the size of the binding post or fastener the connector will be retained under

Insulated ring terminal connectors usually have the insulation color coded for wire size, following this scheme:

RED = 18 to 22-AWG
BLUE = 14 to 16-AWG
YELLOW = 10 to 12-AWG

I recommend using name-brand ring terminals. Very cheap made-in-China terminals may not be made from good cooper, may not be properly tin-plated, and may be heavily oxidized before you even install them. Here is an example of a brand-name terminal for 16-AWG wire and a #8 stud:


Ring terminal connector size can range from 1/2-inch (or larger) to #2 machine screw. Use ring terminal connectors that match the size of the stud or fastener. The typical BLUE SEA SYSTEMS power distribution panel such as Model 5062 12-circuit fuse panel with negative bus and cover will use #10-32 fasteners for the primary power and #8-32 for the branch circuits. Also note that the branch circuit fasteners include captive star washers. Use of star washers in electrical circuit fasteners helps insure that the fastener penetrates any surface oxidation that might exist on the conductors.

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Joined: Fri Aug 31, 2018 3:22 pm

Re: DC Power Distribution Updating

Postby Polarue » Tue Sep 04, 2018 12:59 pm

Nice job there on your boat. The only thing I would add is that if dielectric grease is added as a protective coating against further oxidation, the connection reliability and performance is maintained and extended considerably. In my mind, any electrical connection in a marine environment should have this coating. Some might not choose to use this method due to its messy nature. Do it once and do it the best you can is my motto and the extra time and cost in this case is minimal. I keep a tube handy for all electrical work on my boat or autos and I have never had to clean off any oxidation from any connections that I had previously protected. This silicone based grease seems to attract the dust and dirt less than petrolium based greases.

Posts: 5994
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

Re: DC Power Distribution Updating

Postby jimh » Thu Sep 06, 2018 3:33 pm

I never apply insulating grease to any electrical metal contacts on any sort of power distribution panel. Any power distribution panel should be located in a non-splashing, weather-tight enclosure.

The only place I use an insulating grease is on the rubber or flexible seals of connector bodies—not on the actual connections—and only when the manufacturer calls for it.

Some electrical light bulbs and their associated sockets in enclosures that are not completely sealed may benefit from a coating of an insulating grease.

But I would never use and never recommend slobbering grease onto the power distribution panel screw terminals, wire ring terminals, fuses, and fuse sockets as shown above. A greasy mess results.

If an electrical terminal post must be coated with some sort of protectant after assembly of the wiring, use a spray such as Boeshield T9.