What are the minimum conductor sizes for power and control circuits?

• A. Power circuits #16 AWG; Control circuits #14 AWG
• B. Power circuits #14 AWG; Control circuits #16 AWG
• C. Power circuits #12 AWG; Control circuits #18 AWG
• D. Power circuits #18 AWG; Control circuits #12 AWG

Answer: (B)

The main idea here is that conductor size is chosen to match the current the circuit is expected to carry, using the ampacity ratings of the insulation and temperature rating. Power circuits are designed to deliver more current, so they require a conductor that can handle a higher load. For typical general-purpose power circuits (around 15 A), the smallest copper conductor that safely carries that amount with standard insulation is 14 AWG. Control circuits, on the other hand, carry much less current (think relays and sensing circuits), so a smaller conductor is acceptable, with 16 AWG being a common and sufficient choice.

So, the minimums align with practical current demands: power circuits need at least 14 AWG, while control circuits can use 16 AWG. If a circuit were actually a 20 A power circuit, you’d need at least 12 AWG, and using 18 AWG for power would be undersized for typical loads.