A switch used with high inrush circuits, inductive circuits, or DC motors should be...

A switch used with high inrush circuits, inductive circuits, or DC motors should be...

• A. It should be derated
• B. It should be replaced with a higher rating
• C. It should be insulated with paper
• D. It should be used without derating

Answer: (B)

Switch current ratings must account for startup surges and inductive loads. When a circuit with high inrush, an inductive coil, or a DC motor is energized, the current can spike far above the running current. A DC motor, in particular, draws a large starting current because the rotor is initially stationary and the only current path is the motor’s low wind resistance before back-EMF builds up. These brief but intense currents stress the contacts and can cause overheating, pitting, or welding if the switch isn’t capable of handling them. Therefore, the safest approach is to replace the switch with one that has a higher current rating, providing sufficient margin for both the normal running current and the surge. Derating would reduce the allowable current and doesn’t address the surge, while using a switch without enough rating risks damage and arcing. Insulating the switch with paper is not a remedy for electrical switching stresses.

Switch current ratings must account for startup surges and inductive loads. When a circuit with high inrush, an inductive coil, or a DC motor is energized, the current can spike far above the running current. A DC motor, in particular, draws a large starting current because the rotor is initially stationary and the only current path is the motor’s low wind resistance before back-EMF builds up. These brief but intense currents stress the contacts and can cause overheating, pitting, or welding if the switch isn’t capable of handling them.

Therefore, the safest approach is to replace the switch with one that has a higher current rating, providing sufficient margin for both the normal running current and the surge. Derating would reduce the allowable current and doesn’t address the surge, while using a switch without enough rating risks damage and arcing. Insulating the switch with paper is not a remedy for electrical switching stresses.