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 | 11-54. Relays
9/8/98
AC 43.13-1B
(1) Electromechanical switches range in
sealing from partially sealed to hermetically
sealed. Use a sealed switch when the switch
will be exposed to a dirty environment during
storage, assembly, or operation. Use a higher
level of sealing when the switch will not have
an arcing load to self-clean the contacts. Low-
energy loads tend to be more susceptible to
contamination.
(2) Proximity switches for aircraft ap-
plications typically have a metal face and pot-
ting material surrounding any electronics and
lead wire exits. The potting material should be
compatible with the fluids the switch will be
exposed to in the environment. The plastic
sensing face of some proximity switches may
be subject to absorption of water that may
cause the operating point to shift should be
protected.
a. Use of Relays. Most relays are used as
a switching device where a weight reduction
can be achieved, or to simplify electrical con-
trols. It should be remembered that the relay is
an electrically operated switch, and therefore
subject to dropout under low system voltage
conditions.
b. Types of Connections. Relays are
manufactured with various connective means
from mechanical to plug-in devices. Installa-
tion procedures vary by the type of connection
and should be followed to ensure proper op-
eration of the relay.
c. Repair. Relays are complicated elec-
tromechanical assemblies and most are not re-
pairable.
d. Relay Selection.
d. Switch Installation. Hazardous errors
in switch operation may be avoided by logical
and consistent installation.
“On-off”
two-position switches should be mounted so
that the “on” position is reached by an upward
or forward movement of the toggle. When the
switch controls movable aircraft elements,
such as landing gear or flaps, the toggle should
move in the same direction as the desired mo-
tion. Inadvertent operation of switches can be
prevented by mounting suitable guards over
the switches.
(1) Contact ratings, as described on the
relay case, describe the make, carry, and break
capability for resistive currents only. Consult
the appropriate specification to determine the
derating factor to use for other types of current
loads. (Ref. MIL-PRF-39016, MIL-PRF-5757,
MIL-PRF-6016, MIL-PRF-835836.)
(2) Operating a relay at less than nomi-
nal coil voltage may compromise its perform-
ance and should never be done without written
manufacturer approval.
11-48. RELAYS. A relay is an electrically
controlled device that opens and closes electri-
cal contacts to effect the operation of other de-
vices in the same or in another electrical cir-
cuit. The relay converts electrical energy into
mechanical energy through various means, and
through mechanical linkages, actuates electri-
cal conductors (contacts) that control electrical
circuits. Solid-state relays may also be used in
electrical switching applications.
e. Relay Installation and Maintenance.
For installation and maintenance, care should
be taken to ensure proper placement of hard-
ware, especially at electrical connections. The
use of properly calibrated torque wrenches and
following the manufacturer’s installation pro-
cedures is strongly recommended. This is es-
pecially important with hermetically sealed
relays, since the glass-to-metal seal (used for
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