The NEC permits transformer secondary conductors to be connected without overcurrent protection at the secondary if these conditions are met, which also include ‘all of these’?

• A. Length 10 feet or shorter
• B. Installed in a raceway
• C. Conductor ampacity ≥ the load rating
• D. All of these

Answer: (D)

The NEC allows omitting overcurrent protection on the transformer’s secondary when the wiring is kept within tight limits so a fault on the secondary won’t overheat the conductors and the setup is physically protected. The three conditions ensure safety: keeping the secondary conductors very short (10 feet or less) limits fault energy and voltage drop; installing the conductors in a raceway provides mechanical protection and containment of any fault; and sizing the conductors so their ampacity meets or exceeds the transformer’s secondary load current makes sure they can carry the normal and fault currents without overheating. When all three are met, the secondary can be connected without its own overcurrent device, with the primary protection handling overall fault protection. If any one condition isn’t met, secondary overcurrent protection is required to maintain safety.