combination of both depending on the
(6) Keep the sealing surface of the magnet
sequence required.
core and armature clean.
(2) There are three general types, the butt
(7) Adjust the interlocks so as to make
type commonly used on magnetic
contact at the correct point.
contactors and the sliding type and cam
(8) After the locomotive has been run an
types usually used on pneumatic
inspection can be made of contactor
switches. With the butt type a small metal
condition immediately upon shutdown by
arm is attached to the armature of the
feeling the temperatures of the contacts
switch.
The arm actuates a pivoted
and interlocks by hand; adjust the warmer
insulated block on which are mounted
ones. This same method of inspection
spring supported contacts. As the switch
can be applied to other contacts.
operates, the contacts bridge control
(9) Determine the PULL-IN voltage at
terminals and thus establish the circuit.
overhaul and set the contactor to PULL-IN
With the sliding type, the control wires are
at not more than 60 percent of normal
terminated at compensated fingers
voltage.
mounted on the base of the switch. An
(10) Faulty or erratic operation may occur due
insulated block, which carries small
to too high a PULL-IN voltage or binding
conducting segments, is attached to the
of parts.
piston arm of the switch. As the switch
(11) The arcing shield or chute which
operates the segment slides under two
surrounds the main contacts can be
fingers to complete the circuit. With the
released readily and slid out from its
cam type, the control wires are terminated
position; it is provided for the purpose of
at the stationary and spring fingers
directing the arc and preventing it from
mounted on the base of the switch. A
coming in contact with the blowout poles
block attached to the piston arm carries
and other metal parts of the switch. The
small cams. As the switch operates, the
parts of the arc chute are all made of arc-
cams close or open the spring fingers to
resisting, insulating material, but they will
make or break the circuit to the stationary
gradually wear away necessitating
fingers.
occasional renewing. Renew the sides
(3) Interlocks have a very important function
before they have burned away sufficiently
in the overall performance of the
to expose the metal pole pieces.
apparatus. The failure of an important
(12) Securely fasten the copper shunt which
interlock is sufficient to prevent operation.
carries the current from the moving
Trouble can be avoided by periodic
contact to the contactor terminal, and if
inspection.
broken or badly worn, replace promptly.
b. Inspection. The following examination of the
interlocks should be made at inspection periods:
90. Interlock
(1) See that the control terminals are tight.
a. Description.
(2) See that the interlock contacts are clean
(1) An interlock is an auxiliary switch,
and not worn or burned.
mounted on a main circuit electro-
(3) See that there is a deflection of the spring
pneumatic switch or electro-magnetic
in the interlock finger or bar when the
contactor,
which
establishes
or
contact is made.
disconnects a control circuit at the time of
(a) On the butt type this can be
operation of its particular switch. There
obtained by adjustment of the
are two general classes; the IN interlock,
length of the interlock arm.
which completes a control circuit when the
(b) On the sliding type this can be
main contacts of the switch are closed;
accomplished by putting a slight set
and the OUT interlock which establishes a
in the fingers.
control circuit when the main contacts are
opened.
A single main switch or
(c) On the cam type this can be
contactor can be equipped with IN
accomplished by adjustment of the
interlocks,
OUT
interlocks
or
a
gap between
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