FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 4. Inspection of Circuit-Protection Devices | 11-53. Switches
9/8/98
AC 43.13-1B
armature and field coils is released when the
control switch is opened.
e. Switch Selection. Switches for aircraft
use should be selected with extreme caution.
The contact ratings should be adequate for all
load conditions and applicable voltages, at
both sea level and the operational altitude.
Consideration should be given to the variation
in the electrical power characteristics, using
MIL-STD-704 as a guide.
g. Low Energy Loads. Switches rated
for use at 28 VDC or more, and at 1.0 amp or
more, generally have silver contacts. In gen-
eral, silver contacts should not be used to con-
trol devices which have either a voltage less
than 8 volts or a continuous current less than
0.5 amps unless the switch is specifically rated
for use with low-energy loads. Table 11-5
provides general guidelines for selecting con-
tact materials for low-energy loads, but is not
applicable to hermetically sealed switches.
f. Derating Factors. Table 11-4 provides
an approximate method for derating nominal
ratings to obtain reasonable switch efficiency
and service life under reactive load conditions.
WARNING: Do not use AC derated
switches in DC circuits. AC switches
will not carry the same amperage as a
DC switch.
(1) Typical logic load devices have a
voltage of 0.5 volts to 28 volts and a continu-
ous current of less than 0.5 amps. A suitable
method of rating switches for use on logic load
devices is specified in ANSI/EIA 5200000.
(General specification for special use electro-
mechanical switches of certified quality.)
TABLE 11-5. Selection of contact material.
TABLE 11-4. Switch derating factors.
Nominal
System
Voltage
Type of Load
Derating
Factor
28 VDC
Lamp
8
28 VDC
Inductive (relay-solenoid)
4
28 VDC
Resistive (Heater)
2
28 VDC
Motor
3
12 VDC
Lamp
5
12 VDC
Inductive (relay-solenoid)
2
12 VDC
Resistive (Heater)
1
12 VDC
Motor
2
NOTES:
1. To find the nominal rating of a switch required to operate
a given device, multiply the continuous current rating
of the device by the derating factor corresponding
to the voltage and type of load.
2. To find the continuous rating that a switch of a
given nominal rating will handle efficiently,
divide the switch nominal rating by the derating
factor corresponding to the voltage and type of load.
NOTES:
1. If sulfide, moisture, or any form of contamination is
present, a sealed switch should be used. The degree
of sealing required (environmental or hermetic) is de-
pendent upon the environment in which the switch is
intended to be operated.
2. If particle contamination in any form is likely to reach
the contacts, bifurcated contacts should be used.
3. Low-voltage high-current loads are difficult to predict
and may result in a combined tendency of noncontact,
sticking, and material transfer.
4. High-voltage high-current applications may require the
use of Silver Nickel contacts.
Par 11-53
Page 11-17