Testing Continuity and
Tracing Circuits
T
wo of the most time-consuming tasks for marine troubleshooters are finding
breaks in long circuits and tracing wires through tangled bundles and harnesses
that snake in and out of view as they pass through bulkheads and behind cabi-
netry. Tone-generating circuit tracers and time domain reflectometers (TDRs) are two
modern tools that greatly simplify these tasks.
Like many of the tools in this book, tone-generating circuit tracers and TDRs have been
used for years in other industries, such as IT and telecommunications, before being “discov-
ered” relatively recently by high-end marine electrical technicians. Few marine technicians,
and far fewer private boatowners, have heard of or used these very useful tools.
Without these tools, however, troubleshooters must struggle with a multimeter or
DVOM set to the ohms scale, and run continuity checks one wire at a time. This often
involves dragging an extended connection lead through the boat to attach both ends of the
meter leads to the wire or harness. And even if the continuity test does confirm a break in
the circuit, you are still left wondering exactly where the break is located.
TDRs and circuit tracers eliminate all that work. When connected to one end of a pair
of conductors (and it must be a pair), both devices bounce a signal between the two con-
ductors. When the “bouncing” stops, a fault is indicated. But the similarities end there.
Working from one end of the conductor, a TDR can also identify exactly how far
down the wire run a problem is located. (Amazingly, TDRs have an effective range of
6,000 feet/1,829 m—well beyond the distance needs on boats.) Tone-generating circuit
tracers, in contrast, require access to the entire length of the wire. You connect the trans-
mitter to one end of the conductors, then trace along the wire with the handheld receiver
unit. As long as the receiver sounds off, it is receiving a signal, indicating continuity. When
the noise stops, you’ve found your break.
If access is not a problem, a tone-generating circuit tracer may be easier to use, since it
showsyou the exact location of the fault. If access is a problem, a TDR may more useful
since it tellsyou where the fault is located, as a function of distance from the device. You
then have to find the location, perhaps using a tape measure.
Pricing is another major difference. Unlike many of the other tools discussed in this
book, tone-generating circuit tracers are an extremely modest investment, running in the
CHAPTER
3
Copyright © 2007 by Edwin R. Sherman. Click here for terms of use.