Underground service conductors that supply power to limited loads of a single branch circuit shall not be smaller than _____.

• A. 14 AWG copper
• B. 12 AWG copper
• C. 10 AWG copper
• D. 8 AWG copper

Answer: (B)

The main idea is assigning a safe minimum ampacity for underground service conductors feeding a limited-load single branch circuit. For that scenario, the conductors must be at least 12 AWG copper. This size provides enough current-carrying capacity for a typical limited-load branch circuit (often protected at 20 A) and accounts for the harsher underground environment, moisture, and temperature effects on the insulation. 14 AWG would be too small for this purpose, since it is generally limited to lighter loads (and, in underground service contexts, 12 AWG is the practical minimum). Larger sizes like 10 or 8 AWG are not required for these limited-load cases unless the specific installation demands higher ampacity for other reasons, but the smallest acceptable copper size for this scenario is 12 AWG.