SHORE POWER, from page 1
Marinco, one of the largest makers of
shore power cords, a hot cord is rarely
caused by overloading the circuit; it’s
almost always the result of a damaged
cord, corrosion, or a poor connection.
few weeks later when the owner went
on board and found the cord smoking
where it had been damaged. If he hadn’t
happened to stop by, the cord likely would
have started a fire.
2. Corrosion
a tight-fitting waterproof cap and be sure
it’s closed after disconnecting the cord
and before leaving the dock. Corrosion
typically builds gradually; make it a habit
to examine the blades whenever you
connect or disconnect the cord.
3. Pitting
Three Ways Resistance
(and Maybe a Fire)
Is Created
1. Damage
Cords are most often damaged when
they’re pinched between the dock and
boat. Cords need to have enough slack
to rise and fall with the tide and the
movement of the boat, but not enough
to get caught on the dock. Cords can be
hung neatly with Velcro fasteners along
the boat’s railing so that there is minimum
Corrosion is usually only a problem at the
cord’s connections. Corrosion doesn’t
conduct electricity well, and like broken
wire strands, it causes resistance. Shore
power connections are supposed to be
moisture-proof, but often the locking
rings are damaged or are not used,
which can expose the connection to the
environment. Corrosion might not be
obvious; look at the blades that go into
the shore power receptacle and the ones
on the boat’s inlet. Bill Drake says that the
blades are usually nickel-plated brass;
after years of plugging and unplugging,
the nickel can eventually wear through,
is the area that gets overheated and
just replacing the cord won’t solve the
problem—the inlet likely will have to be
replaced as well. Make sure the inlet has
A bad connection—whether from
corrosion or loose contacts—can cause
arcs, which are like tiny lightning bolts
between the contacts in the connection.
Arcing causes pitting, which, like
corrosion, leaves less contact surface
and increases resistance. After plugging
in a cord, make sure the connection is
locked tightly in order to prevent a poor
connection.
which is an indication
that the cord needs to be
replaced. Using an abrasive
such as an emery cloth to
clean the blades is a bad
idea, he says, because it
will remove the coating.
Poor contact can manifest
itself as discoloration or
melting around the base
of the blades, which is a
clear indicator that the
cord must be replaced
immediately. Drake
cautions against replacing
an overheated cord
without knowing what
caused the problem. The
claim files show that most
often, the boat’s inlet
Arcing also occurs (big time) when a cord
is disconnected while the circuit is still energized. To prevent arcing, either turn the
power off at the shore power pedestal or
turn off the boat’s AC breaker before unplugging or plugging in either end. Failure
to do so is the main cause of arcing damage. Blades damaged by arcing can’t be
salvaged because the metal is damaged
and the coating is ruined.
Keeping Power
Cords Healthy
Examining Your Cord
sagging when it finally crosses over the
water to the pedestal.
Another way cords get damaged is when
owners forget to disconnect them before
casting off the lines and exiting the slip.
One skipper found out the hard (and
embarrassing) way that a shore power
cord is strong enough to completely stop
a boat; not only was the cord damaged,
the boat slammed into a piling after being
caught up short. Even a relatively minor
tug can break strands internally or at the
connection ends. And because cords
have thick insulation, internal damage
is often impossible to see. Broken wire
strands make the wire effectively thinner,
which can dramatically increase the
resistance of the cord. Don’t take the
risk; if your cord gets severely pinched
or stretched, it should be replaced. In
one claim (#0102569), a cord that had
been pinched at the dock was put back
into use. It worked fine until one day a
This infrared photo shows heat that the naked eye can't see.
Heat build up is caused by resistance from damage, corrosion, or pitting. Inspect the connections—on the boat and the
dock—routinely and replace any that show signs of damage.
To get an idea of your cord’s condition,
start at the ends and look for brown
discoloration at the base of the blades. Any
brown or black discoloration at the blades
indicates excessive heat. Blades with a
worn nickel coating or pitting (caused by
arcing) are another red flag. If any of these
conditions exist, don’t use the cord.
Note that damaged cord ends can often be
replaced. Check with the manufacturer to
Photos: Sam Scudder
This inlet looks like it only has minor damage, but closer inspection of the other side shows that
the damage is far worse. Any heat-damaged connections must be replaced immediately, before
the cord is used again – and the reason for the damage has to be determined, otherwise the
connection will fail again.
