Checking Relays - Kubota u15-3 Workshop Manual

5. Checking relays

1) When current flows through the coil of a relay, its core is
magnetized to attract the iron piece, closing (ON) the con-
tact at the tip of the iron piece. When the coil current is
turned off, the iron piece is made to return to its original
position by a spring, opening the contact (OFF).
2) By using a relay, a heavy current can by turned on and off
by a switch of small capacity. 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 at this
time to the switch is the relay coil current only and is very
small.
3) The relays may be classified into the normal open type
and the normal close type by their contact construction.
NOTE
The deenergized state means that no current is flowing
through the coil and the energized state means that cur-
rent is flowing through the coil.
When a normal close type relay as illustrated here is
checked, there should be continuity between terminals (1)
and (2) and between terminals 3 and 4 when the relay is
deenergized, and the continuity should be lost between
terminals 3 and 4 when the battery voltage is applied to
the terminals I and 2. A relay can be checked in this man-
ner and it cannot be determined if a relay is okay or faulty
by checking its state only when it is deenergized (or ener-
gized).
II-173
WSM U15-3