In any given year, I inspect quite a few boats. These range from simple tenders to extremely complicated power and sailing yachts. When it comes to electrical systems and their installations, I keep a watch- ful eye out for not only compliance with American Boat & Yacht Council (ABYC) and international standards but also simple workmanship and the application of best industry practices. Let’s get a look at some
of the common issues I encounter and consider the problems they can create.
Motor Circuits And The “Locked Rotor”
Without question, one of the most common issues I run into is the over-fusing of
small DC-motor circuits, which happens when someone installs a fuse with a higher
amperage rating than what’s recommended. The motors you have on board to run
your bilge pump, livewell pump, bilge blower fan, or maybe a macerator pump for your
head system all have a fuse rating printed on the label. Motor circuits are different
from all of the other electrical circuits on your boat because installers need to worry
Negligence Can Cost Plenty!
Problems in your boat’s electrical system can destroy your pride and joy.
Be especially careful around these common problem areas
about protecting the device as well as the
wire runs supplying power. Here’s why.
In the case of a jammed pump, the
motor is trying to turn but can’t due to
a piece of debris wedged between the
impeller and the housing. If the installed
fuse is rated higher than the manufacturer’s maximum fuse size, it won’t trip and
open the circuit. If the fuse doesn’t blow,
power will continue to flow to the motor
and it will begin to overheat, ultimately
catching fire. The inevitability of a fire
is predicted by applying a fundamental
electrical law, Ohm’s law. This states that
as voltage remains constant and electrical
resistance increases, the current decreases.
In this case, as the motor heats up, its
resistance increases, and the current is
quite quickly reduced to below the trip
threshold for the fuse. Motors provide a
maximum fuse size on the label. Make
sure each of your fuses matches the
motor recommendation exactly.
Replacing A Battery Charger
When installing a new battery charger on
your boat, there’s a lot more to consider
than just mounting the unit, connecting positive and negative cables to your
By Ed Sherman
problems can be
traced to poor battery installations.
Make sure that
battery cables are
well secured and
free of corrosion.
This pump melted when the impeller
jammed. Without proper circuit protection,
a fire could be the result.