82 electrical systems troubleshooting
office buildings for some time, and may
account for the seemingly strange symptom of
a burned-up neutral conductor with all other
conductors in the system looking fine.
The most common transformer type used in
commercial and industrial environments is
known as a Delta-to-Wye transformer, in which
the transformer’s primary windings are in a Delta
configuration, and the secondary windings are in
a Wye (see illustration). We can see that the neu-
tral has to serve each of the three hot-wire legs to
get the current back to its source; i.e., the trans-
former. Since this neutral conductor is typically
the same gauge as the hot wires, it’s easy to see
how it might be overburdened at times.
Transformer overheating is not only another
effect of harmonic distortion exposure, it pre-
sents another potential problem on boats that
use transformers for shore-power isolation
and/or as voltage step-up or step-down devices.
The infrared heat gun discussed in Chapter 5 is
a great tool for determining whether a problem
exists. Temperature readings greater than 120°F
to 125°F (49°C to 51.7°C) indicate either a
transformer that is underrated for the task at
hand or is exposed to excessive harmonics.
Harmonic distortion was of little con-
cern to boatowners and technicians whenthe AC load on boats was typically only a
water heater, perhaps an electric stove, and
maybe a TV. But as we’ve discussed, the
equipment on boats has gotten more sophis-
ticated, and consequently more sensitive to
distortion in its power supply. So it is now
important for the advanced technician or
boatowner to have an understanding of har-
monics to ensure the safety and reliability of
AC systems.Value and Utility
If you regularly work on larger boats or boats
with AC generators, inverters, or any combi-
nation thereof, I recommend that you con-
sider investing in an oscilloscope. If time is
money, and most say it certainly is, then you’ll
find that a small scope will answer some key
questions about power supplied to the boat
veryquickly and easily. As boats get more and
more sophisticated, and we find ourselves
working on 35-footers equipped with multi-
ple AC power sources, flat-screen TVs that
rise up out of a saloon table, and high-end
audio systems, etc., the value of using a scope
will become evident in no time at all when
problems occur.208 V208 V208 V120 V120 V120 VA"WYE"BCACBDelta configuration—primary side of transformer Wye configuration—secondary side of transformerneutralA Delta-to-Wye transformer showing the differences in configuration between the primary and secondary windings of the unit.