The voltage rating of motor controller holding coils is:

• A. not important if the control circuit is isolated
• B. not necessarily the same as the motor supply voltage
• C. always less than the motor supply voltage
• D. always the same as the motor supply voltage

Answer: (B)

The key idea is that the holding coil is driven by the control circuit, not by the motor’s power supply. The coil’s voltage rating must match the voltage used to energize the control circuit (for example, a 24V control supply), which can be separate from the motor’s supply voltage. Because of this separation, the holding coil voltage does not have to equal the motor supply voltage; it only has to be compatible with the control circuitry that drives it. The other options imply fixed relationships that aren’t required: isolation doesn’t remove the need for a suitable coil voltage, and the coil voltage is not universally required to be less than or equal to, or always equal to, the motor supply.