What voltage is common for control circuits in LV systems?

• A. 24 V DC
• B. 120 V AC
• C. 240 V DC
• D. 12 V DC

Answer: (A)

Control circuits in low-voltage installations are designed to be safe to handle while still reliably driving relays, contactors, PLCs, and sensors. A 24-volt DC supply hits the sweet spot: it keeps shock risk low, supports easy safety compliance, and provides enough voltage to operate coils and digital electronics without needing bulky safety measures. There’s broad compatibility—relays, contactors, PLC I/O modules, sensors, and power supplies are widely available and standardized for 24 V DC—making it the practical default for LV control circuits. Higher voltages like 120 V AC or 240 V DC require more insulation and safety precautions, and while 12 V DC exists, it doesn’t offer the same universal component availability and ease of integration.