To locate the source, do the following:1 Shut off the main AC breaker to the boat.
If the residual current reading goes to
zero, then it’s a fair bet the source of the
current leakage is on board the boat.
2 So next, turn the main breaker back on.
3 Then turn off the breakers to the boat’s var-
ious branch circuits one breaker at a time.
4 If the current reading suddenly goes to
zero when you turn off a breaker, you’ve
identified the problem circuit. Most often,
the leakage current is coming from an
appliance on the circuit, and the appliance
itself may warrant further testing to check
for leakage right at the device.
5 If turning off breakers and switches pro-
duces no change in the residual current at
the shore-power cord, then the source of
the leakage current is another boat plugged
into the same shore-power circuit.
6 Try to isolate the problem by unplugging
each boat at the dock, one by one (see
below).
7 If the reading on your amp clamp goes to
zero, you’ve found the culprit.
It’s also likely that the reading may get dra-
matically lower but not drop to zero because
there is a real possibility the source of leakage
is more than one boat, and that what you are
reading on your meter is the cumulative leak-
age of multiple faulty boats. To protect your
boat, you may need to gain access to several
others. Did I mention inconvenience?
Since you can’t just turn off the power to
everybody’s boat without getting permission,
I generally notify the marina operator that a
serious safety problem exists that needs imme-
diate attention. The manager should immedi-
ately prohibit swimming from the docks until
the problem is resolved, and if the marina
testing for residual current 97operator is serious about customer service and
customer safety, he or she will promptly grant
you the permission you require. If you need to
make your case more strongly, report your
own leakage test results in the context of
Table 10-1, which shows the very low levels of
current capable of causing death.
Measuring Voltage Potential
Although you can’t measure current flow
through the water by any simple method, you
can measure voltage potential. We are actually
more concerned about voltage potential any-
how. In this case, we are concerned about elec-
trical shock hazard and voltage potential
applied to human bodies as they swim
through the water. The actual current flow
through the body will vary depending on the
person, and factors such as skin resistance and
how long the person has been in the water will
determine actual current exposure. All you
need to test this is a conventional DVOM set
to the VAC scale and an extended lead for the
hot terminal. Additionally, a broomstick is
quite helpful to make an extension probe for
the meter (see the sidebar on page 98). With
these tools, follow these steps:1 Confirm the integrity of the ground with
the SureTest tool.
2 Attach the hot lead of the DVOM to the
end of the broomstick, leaving the con-
ducting tip exposed.
3 Plug the meter’s other lead into the
grounding terminal on the shore-power
pedestal.
4 With the meter set to VAC, probe the
water around the dock and boat looking
for a VAC reading.
5 You won’t see a solid 120 or 220 VAC
reading, but you could easily see 60 to
100 VAC if a problem exists. If that’s the
case, immediately notify the marina