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Amtrak Signal Maintenance Training – Level 1 (SMT-1) Practice Test

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Which component is commonly used to snub the drop across a relay coil?
Correct Answer:
Diode
Explanation:
When a relay coil is switched off, the inductor tries to keep current flowing, creating a voltage spike (back-EMF). A diode connected across the coil, reverse-biased during normal operation, provides a safe path for that current as the field collapses. The current circulates through the diode back to the power rail, clamping the voltage to a value near the supply plus a diode drop and letting the energy dissipate gradually. This protects the driving transistor and the contacts from arcing and voltage damage. The flyback diode is the common, reliable snubber for simple relay protection. Capacitors and resistors can be used in other snubber arrangements, but they don’t provide the same straightforward, bounded path as a diode across the coil.

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