Since the SureTest 61-164 will also mea-
sure peak voltage, you can get a feel for dis-
tortion by calculating the theoretical peak at
line voltage 1.414, and comparing it to the
actual measured peak. You won’t be able to
see the distortion as you can with the oscillo-
scope, but you’ll be able to determine if it
exists, and calculate it if it is excessive (see
Chapter 7).
Besides basic line voltage and peak val-
ues, the unit will also test for neutral-to-
ground leakage. (Press the “advance” arrow
key to go to the next test in the sequence.)
This value should always be less than 2 VAC.
More than 2 VAC is an indication of exces-
sive current leakage from neutral to ground.
This condition is typically caused by the
breakdown of insulation within an appliance,
or possibly by two terminals that are barely
testing ac and grounding systems 51Always look for labeling on the back of an appliance for
grounding instructions, and be absolutely certain that the
neutral-to-ground link is disconnected on a boat installation.
touching, creating a partial, though high-
resistance, connection. In a 220 V multiple-
phase system, high neutral-to-ground leakage
could indicate severely unbalanced legs
between the phases or excessive harmonic dis-
tortion on the shared neutral. These conditions
can create equipment performance problems,
as described in Chapter 7.
Table 4-1 on page 52 summarizes voltage
readings, expected results, problems, and pos-
sible causes and solutions.Voltage Drop Measurements
As already stated, excessive voltage drop is one
of the marine electrical system’s biggest ene-
mies. I’ve also noted that the primary by-
product of excessive electrical resistance is
heat, and that too much voltage drop is the
same as excessive resistance. This is an area
where the SureTest really shines. As far as I
know, it’s the only test instrument that can apply
a load to the wiring at three levels (12 amps,
15 amps, and 20 amps) and calculate the voltage
drop as a percentage within a few seconds.
With this information in hand, trou-
bleshooting is easy. Based on NEC recom-
mendations, anything in excess of 5% is too
much. If excessive voltage drop exists, it may
mean that the wire gauge is too small for the
task at hand, or there is a poor-quality con-
nection somewhere in the circuit. To confirm
or reject this, simply retest at points closer to
the source and see if the problem goes away as
you get closer to the source. If it does, then
the problem is between the high-reading
checkpoint and the low-reading checkpoint,
with several possible causes:- a loose connection in that leg of the
circuit - undersized cabling, perhaps added to the
original circuit - a faulty receptacle that needs replacing