applied to either the red probe or the black probe. This
illustrated in figure 2-33. An installation might have
tester is designed for operation of 28 to 550 volts ac
several feeder distribution boxes, each supplying six
or 28 to 600 volts dc.
or more branch circuits through branch distribution
Before being taken from the shop and used on a
circuit, a voltage tester must be tested for proper
Fuses F1, F2, and F3 (fig. 2-33) protect the main
operation on a known voltage source, such as the
feeder supply from heavy surges, such as short circuits
electric shop test panel.
or overloads on the feeder cable. Fuses
protect branch No. 1. If trouble develops and work is
If your voltage tester is inoperative, turn it in to
to be done on branch No. 1, switch S1 may be opened
your leading petty officer.
to isolate this branch. Branches 2 and 3 are protected
Never use a lamp in a "pigtail" lamp holder as a
and isolated in the same manner by their respective
voltage tester. Lamps designed for use on low voltage
fuses and switches.
(120 volts) may explode when connected across a
VOLTAGE TESTER.-- The most commonly
higher voltage (440 volts). In addition, a lamp would
used voltage tester now available to the fleet is the
only indicate the presence of voltage, not the amount
multifrequency type. This tester has electronic
of voltage. Learn to use and rely on standard test
circuitry and glow lamps to indicate voltage,
frequency, and polarity. One, two, or three lamps are
BRANCH CIRCUIT TESTS.-- Usually, recep-
used to indicate the ac or dc voltage. The other lamps
tacles for portable equipment and fans are on branch
identify the ac frequency (60 or 400 Hz) or whether
circuits separate from lighting branch circuits. Test
the dc circuit being tested has negative polarity
Figure 2-33.--Three-phase distribution wiring diagram.