Front Panel; (A) Generator Output Monitors (Meters); (B) Meter And Line Switches - Hobart 60PL20 Operation And Maintenance Manual

E. Control Box Assembly
The control box (Fig. 6) is a sheet metal enclosure which houses and provides mounting facilities for
generator controls, and engine and generator monitoring equipment. For access to components
mounted inside the control box, it is necessary to remove two 1/4 X 20 - 1/2-inch hex bolts, and to pull
down the front panel, which is hinged to the control box at the bottom.

(1) Front Panel

(a) Generator output monitors (meters)

The generator output is monitored by three instruments; a frequency meter (2) , a voltmeter
(3) , and an ammeter (4) The frequency meter is a resonant-reed type, and indicates the fre-
quency of the generator output alternating current in the range of 380 to 420 Hz (cycles per
second) . The voltmeter indicates the generator output voltage in each phase-to-neutral (A-N,
B-N and C-N) or phase-to-phase (A-B, B-C and C-A) as selected by the meter selector switch
(5) and the line selector switch (7) . (These switches will be described below.) The voltmeter
has a 3-1/2-inch face and the scale is graduated 0 to 300 V. The ammeter is also 3-1/2-inch
size and is graduated 0 to 500 A. The amperage value in each of the three phases may be
read on the ammeter by selecting the desired phase with switch (5) . Three ammeter current
transformers, located beneath the generator control box support panel, lower the output load
current to a lesser value, of definite ratio, which will operate the ammeter movement without
damage. The ammeter dial scale is graduated and numbered so that the pointer will indicate
the true load current value rather than the meter movement current.

(b) Meter and line switches

These switches provide a means of selecting and determining which phase of voltage and
current is indicated on the voltmeter and ammeter and whether the voltage is line-to-neutral
or line-to-line The meter switch (5) is a four-position, rotary type. A nameplate (6) , located un-
der the switch knob, is marked and lettered to indicate the three functional positions of the me-
ter switch. (When the knob is pointing straight DOWN, the switch is OFF.) The line switch (7)
is a two-position, toggle switch used to select either line-to-neutral or line-to-line voltage to the
voltmeter. The nameplate is also marked to indicate position of this switch.
(c) Instrument light
A shielded, instrument panel light (1) is mounted at the left side of the control panel to illumi-
nate controls, instruments, and indicator lights. It is controlled by a toggle switch on the en-
gine control panel (3, Fig. 8) which also controls instrument light on the engine control control.
(d) Indicating lights
The function of these lights (10, 11, 12, 13 and 14) is to indicate, to the operator, the abnor-
mal condition of overvoltage, underfrequency, etc., which caused the protective monitor sys-
tem to function. Each of the five lights is connected to an actuating circuit within the memory
and time delay module. When one of the circuits is activated, it turns on the applicable indicat-
ing light. The light will remain on until the reset switch (17) is pushed. All lamps in indicating
lights may be tested by pressing switch (16).
(2) Control box internal components (Figure 7)
Internally, the control box contains a solid-state voltage regulator, and electrical and safety de-
vices designed to protect the aircraft electrical system against damage which could result from
overvoltage, undervoltage, overfrequency, or underfrequency. Also contained therein are devices
for the protection and control of the generator output electrical system.
December 31/91 Revised
OM-2053
1-1
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