Master Electrician Practice Exam

Under what condition do conductors tapped from a feeder and supplying the primary of a transformer not need overcurrent protection?

1. When they are longer than 25 feet

2. When they have an ampacity of at least one-third of the overcurrent device rating

3. When they are installed in raceways

4. When they are insulated

The correct answer is: When they have an ampacity of at least one-third of the overcurrent device rating

The condition under which conductors tapped from a feeder and supplying the primary of a transformer do not require overcurrent protection is when they have an ampacity of at least one-third of the overcurrent device rating. This is based on the requirements outlined in the National Electrical Code (NEC), which allows for this exemption in certain circumstances. When the ampacity of the tapped conductors is at least one-third of the rating of the overcurrent device, it indicates that the conductors are capable of carrying a significant portion of the load. This arrangement is intended to prevent the conductors from being overloaded. Therefore, if the taps meet this specific criterion, they are considered adequately protected by the functioning of the feeder overcurrent device, negating the need for additional protection specifically for those tapped conductors. In contrast, the other options do not align with the NEC guidelines concerning overcurrent protection for tapped conductors. The length of the conductor, being installed in raceways, or the insulation type do not satisfy the criteria necessary to exempt the conductors from overcurrent protection. Understanding these distinctions is crucial for safely implementing electrical installations and ensuring compliance with regulatory standards.