Marine Electrical Wiring

During recent meetings and gatherings we’ve been asking your —_ environment and are reasonably knowledgeable in determining
opinion on ways to broaden the appeal for this newsletter. the right size for a given application. BUT —if they say they
Several folks have suggested that articles on various marine don’t know, or you are not confident with their judgment don’t
systems or boat maintenance may be beneficial. Hopefully, this buy. Remember the boat you sink may be your own! There are
column will be a forum for sharing the vast range of practical a lot of good books on the market that will help you pick the
experience accumulated by our membership. It is also intended right size wire.

to be the place where you, the reader, can submit technical Always run wire from a fuse or circuit breaker on the main
questions and either obtain answers or direction to appropriate power distribution panel. The only exception to this general
reference material. tule may be the wiring for the bilge pump and its’ switch. If

Of course since I was among the first to suggest such an you are connecting directly to the battery make sure that its
article, I was elected to write the first one. Having no more in-line fuse is located as close to the battery as possible. New
direction than to “fill about a page” gave me license to write boats are usually supplied with circuit breaker panels. The
about a subject that I always seem to be questioned on, namely, circuit breaker should be rated to protect the wire hooked to it,
marine electrical systems. Unfortunately one page won’t be not the device that is being connected. In a properly designed
quite enough room. So in order to keep things manageable, and system the device or instrument has its own fuse, either internal
give me more material for future pages, I’ve divided “marine _to the instrument or supplied externally as an in-line fuse. In
electrical systems” into the six topics that seem to be trouble most cases the fuse supplied with the equipment will protect it
areas for the average boaters. These are; electrical wiring, better than a circuit breaker. The circuit breaker and fuse
alternators and regulators, batteries, grounding and bonding, _ should always be connected to the positive (+) side of the line.
radios and antennas, and instrumentation (depth, speed, GPS, (Note: In the extremely rare circumstance that your boat has a
LORAN, etc.). positive ground system, call me, I would like to see it!) Most

Have you ever watched someone with an electrical problem —_ wiring schemes use white and black or red and black insulation
step out of their boat with that look that says “there be monsters on the multi-strand tinned wire to identify its polarity. A cover-
there”? Usually the look is followed immediately by the ing of gray or tan PVC insulation further protects these wire
question “Hey, do you know anything about …….?”. 90% of the pairs. The black wire is normally the negative (-) side that is
time the problem is easy to fix (provided you have enough connected via a bus bar and heavy wire cable to the negative
money). The biggest contributor to most of the problems I’ve _ side of the battery, or a common point such as the engine block.
witnessed is the wiring that hooks everything together or the The white or red wire is the positive (+) side which is connected
connectors used to join the wires to the devices. Corrosion, to the positive side of the battery via the circuit breaker panel.
improper wire, undersized wire, over-rated circuit breaker and If you are not sure of the polarity of the wiring DON’T HOOK
fuses, and generally poor wire installations are the “monsters” ANY NEW EQUIPMENT TO IT! Reversing the polarity of the
that you can control if you know the right way to do things and wiring to expensive electronics equipment could cause signifi-
the things to avoid. cant damage to it and your wallet.

Never use solid wire on a boat. Solid wire is great for the Wiring systems should be well laid out with the wires neatly
house or barn. They don’t move or flex very much (or at least bundled and supported. Always run the wire in its’ PVC jacket
you hope they don’t). Boats on the other hand are subjected to all the way from the equipment to the circuit breaker panel and
all the abuse that the provides, plus the vibration of an _then open the jacket to connect the white wire to the circuit
engine in most boats. Solid wire cannot survive in this environ- breaker (+) and black wire to the negative (-) bus bar. Never,
ment for very long without fracturing. The only wire that never run a single positive wire from the circuit breaker panel
should be used is multi-strand copper wire that will flex with to a piece of equipment and connect the negative side to another
the boat. Ideally you should use tinned multi-strand copper black wire or your radio ground plate. If you do (or, God
wire. It has a silvery looking coat of tin alloy on each strand of forbid, have) disconnect the wire immediately. This condition
wire and withstands the corrosive marine environment very can set up an enormous electrolysis problem for all the under-
well, water metal fittings, the engine and saltwater cooled heat

Always use wire that is large enough to handle the peak exchangers.

current load of all devices that will be connected to it. The Always run the wires in pairs all the way back to the circuit
maximum current rating for a wire is dependent on the size of _ breaker panel and negative bus bar. Ideally, groups of wires
the wire and its length. Using too small a wire will result in a should be wrapped with tie-wraps every foot or so, or spiral
voltage drop at the device end of the wire that may cause erratic wrapped, and secured to a bulkhead or structural part of the
operation. Even worse, the wire can overheat to the point of boat to reduce the effects of vibration on the wire. One word of
melting the insulation, causing a potential short circuit, and the caution – avoid wrapping AC conductors and DC conductors in
fire that could result would certainly ruin your day. Most the same bundle. Run side by side for any appreciable length
marine stores only carry wire that is meant for the marine (Continued to Page 6)

you can induce quite a bit of noise into the DC wires connected
to the instruments. When we talk about radio installations in
future articles I’ll point out some other conditions to avoid
relative to the radio frequency energy given off by the radio,
antennas and antenna cables. As I pointed out earlier there are
many excellent references on the subject of boat wiring. The
“12 Volt Bible”, “Boatowners Illustrated Handbook of Wiring”,
and other books are available from most good chandlers and
catalogs. Gordon West’s articles in “Sail Magazine” are excel-
lent references, and well worth reading. In fact, the Dec ’97
and Jan ’98 issues of “Sail Magazine” carried two excellent
articles complete with illustrations and further references.

Hopefully this “about a page” long article has stirred up some
questions. Certainly your electrical system should not be
viewed as a “monster”. With a little knowledge and occasional
tender loving care you can easily tame it and save yourself some
money in repair bills.