Reverse Current Diodes—
SNs 24-190 through 24-229, and
SNs 25-030 through 25-064
Two reverse current diodes are installed on the
aft side of the engine beam (one for each gen-
erator system). The reverse current diodes iso-
late the generator systems from each other.
Generator Reset Switch
Operation—SNs 24-190
through 24-229, and
SNs 25-030 through 25-064
Two generator reset switches (Figure 2A-4),
one for each generator, are installed on the
s w i t c h p a n e l a d j a c e n t t o t h e r e s p e c t iv e
GEN–OFF–START switch. Each switch is a
two-position momentary-type switch. When in
the RESET position, the switch completes a
ground circuit that resets the generator over-
voltage relay. On prior airplanes, the genera-
tor reset switch is not installed. Resetting is
accomplished by placing the GEN switch to
OFF, then back to ON.
Indicators
A red generator off warning light above the
generator switch on SNs 23-003 through 24-
142, 24-145, 24-147, 24B-188, and 25-003
indicates the generator is off the line. An amber
GEN OFF warning light on the glareshield
warning light panel on all other airplanes in-
dicates the generator is off line. These lights
also illuminate if the generator switch is in
OFF.
Two ammeters, one for each generator, indi-
cate the load, in amperes, being carried by the
generators. The load indication is taken from
the generator field coil. Generator voltage is
displayed on the DC VOLTS meter and meas-
ures the voltage on the battery charging bus.
CIRCUIT COMPONENTS
Current Limiters
A current limiter panel is installed on the gen-
erator control box in the tail compartment. A
current limiter is like a slow-blow fuse; once
a current limiter has blown, it must be re-
placed. Current limiters are used to provide
power to certain systems, to back up circuit
breakers, and to interconnect buses.
Relays
Relays are used at numerous places through-
out the electrical distribution system, partic-
ularly in circuits with heavy electrical loads.
The relays function as remote switches to
make or break power circuits. This arrange-
ment allows the control circuit wiring to be a
much smaller gage and requires much less
current to operate the relay.
Overload Sensors—SNs 24-190
and Subsequent, and
SNs 25-030 and Subsequent
Overload sensors are used in the power circuits
to the left and right feeder buses. These over-
load sensors react thermally to electrical loads
in excess of 70 amperes. They electrically
ground the relay control circuit and cause the
associated control circuit breaker to trip, caus-
ing the relay to open and break the power cir-
cuit. Once the overload condition has been
removed, the overload sensor cools and re-
sets automatically; however, the failed control
circuit breaker must be reset manually.
Circuit Breakers
Push-pull circuit breakers protect all electri-
cal systems in the airplane. On SNs 23-003
through 24-129, the circuit breakers are in the
tail compartment on the generator control
panel and on the copilot’s armrest in the cock-
pit. On SNs 24-130 through 24-229, and 25-
003 through 25-064, circuit breakers are
located on the left side wall of the baggage
compartment and at the copilot’s armrest area
of the cockpit. The DC circuit breakers are
thermal, and the AC circuit breakers are mag-
netic. The amperage ratings are stamped on the
top of each circuit breaker. Figures 2A-5
through 2A-13 illustrate the circuit-breaker
panels by model and serial number.
2A-5
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
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