Understanding Relays

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PRACTICAL TESTING
Once the pins have been identified, energize the control circuit by supplying B+ to pin 1 and a ground to pin 3. A faint "click" will be heard; although this "click" means the switch has moved (closed), it does not mean the relay is good. The load circuit switch contacts could still be faulty (high resistance), and further testing is required. A common mistake technicians make is they hear a "click" and assume the relay is good. Take the extra step and verify operation.

CAUTION
Testing relays with built in clamping diodes require a special procedure. These relays are polarity sensitive; placing B+ to the wrong pin (backwards) while performing a practical test will forward bias the diode and damage the diode, thus destroying the protective quality of the diode.