Which device is commonly used to isolate control signals from the load in relay circuits?

• A. Opto-isolated relay
• B. Magnetic starter
• C. Pushbutton
• D. Thermal relay

Answer: (A)

Isolating control signals from the load is achieved with opto-isolation. An opto-isolated relay uses a light-emitting diode on the control side and a light-sensitive detector on the load side, so the control signal is transferred as light rather than a direct electrical path. This provides electrical separation between the low-voltage control circuitry and the high-load circuit, protecting the control side from voltage spikes, noise, and ground potential differences that can come from the load.

Magnetic starters simply use a coil to energize a contactor; they don’t provide inherent electrical isolation between control and load. Pushbuttons are input devices and don’t offer isolation by themselves. Thermal relays protect motors from overheating and act as protection devices, not isolation elements.