What is the purpose of a snubber across a relay coil?

• A. To increase coil current.
• B. To provide a backup power source.
• C. To physically protect the coil from mechanical damage.
• D. To suppress voltage spikes (back-EMF) when the coil is de-energized, reducing arcing and EMI.

Answer: (D)

When a relay coil is de-energized, the inductive nature of the coil tries to keep current flowing and generates a high voltage spike (back-EMF). This spike can arc the contacts and create EMI and voltage transients in the control circuit. A snubber across the coil provides a safe path for the energy to dissipate, so the voltage spike is limited. Depending on the type, an RC snubber, a diode (with possible resistor or Zener), or a varistor clamps or slows the collapse of current, allowing the coil current to decay smoothly instead of spiking sharply. This reduces arcing at the switch contacts and the associated electrical noise. The other options don’t address the spike: a snubber isn’t meant to increase coil current, supply backup power, or physically protect the coil from mechanical damage.