1629 / 1906
ELECTRICAL
327
CHECKING RELAYS:
1.
By using a relay, a heavy current can be turned
on and off by a switch using much less current.
For example, in the circuit shown here, when the
switch is turned on (
closed
), current flows to the
coil of the relay. Then, its contact is turned on
(
closed
) and the light comes on. The current
flowing through the switch is much less than that
for the light.
2. Relays may be classified as the normally open-
type or the normally closed-type, depending on
their contact construction.
NOTE
The De-energized state means that no current is
flowing through the coil. The energized state
means that current is flowing through the coil.
(a)The normally open-type
When a normally open relay as illustrated here
is checked, there should be no continuity
between terminals 30 and 87 when the relay is
de-energized. There should be continuity
between terminals 30 and 87 when battery
voltage and ground are applied to terminals 85
and 86. The relay condition is determined by
this check.
NOTE
Check the relay in both condition, i.e. energized
and not energized
(b)The normally closed-type
When a normally closed relay as illustrated
here is checked, there should be continuity
between terminals 30 and 87 when the relay is
de-energized. There should be no continuity
between terminals 30 and 87 when battery
voltage and ground are applied to terminals 85
and 86. The relay condition is determined by
this check.
NOTE
Check the relay in both conditions, i.e. energized
and not energized.