This type of solid-state relay uses a magnetic field to isolate the control circuit from the load?

• A. Reed-controlled AC relays
• B. Opto-isolated relay
• C. Triac-based AC relays
• D. Solid-state DC relay

Answer: (A)

Isolation between control and load can be achieved when a magnetic field, rather than a direct electrical connection, moves the switch contacts. In a reed-controlled relay, energizing a small coil generates a magnetic field that pulls sealed reed contacts together inside a glass envelope. The coil and the contact circuit stay electrically separate, so there’s galvanic isolation between the control side and the load side even though they interact magnetically. This magnetic actuation is what makes the control and load circuits physically isolated while still allowing reliable switching.

Other options rely on different isolation methods or switching mechanisms. An opto-isolated relay uses light to transfer the signal across an isolation barrier, not a magnetic field. Triac-based AC relays and solid-state DC relays rely on semiconductor switches and don’t use magnetic coupling to isolate the control and load circuits.