Figure 2-33.--Three-phase distribution wiring diagram.

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

boxes.

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.

and

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,

equipment.

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.

2-22