Master Electrician Practice Exam

What is the minimum ampacity required for a 25 ft. long tap conductor tapped from a 100 ampere rated feeder?

1. 25 amperes

2. 30 amperes

3. 33.3 amperes

4. 40 amperes

The correct answer is: 33.3 amperes

To determine the minimum ampacity required for a tap conductor from a 100 ampere rated feeder, it’s essential to understand the National Electrical Code (NEC) regulations regarding tap conductors. According to NEC, a tap conductor must be sized based on the load that it will carry and the length of the tap. In this context, taps are allowed to use a smaller conductor size under certain conditions. Generally, for a tap from a feeder, the tap conductor must be rated for at least one-third of the feeder's total amperage if the tap is 25 feet, as with this case. Calculating one-third of 100 amperes gives us approximately 33.3 amperes. This means that a tap conductor tapped off of a 100-amp feeder can be sized down to a minimum of 33.3 amperes, ensuring safety and compliance with the NEC. This minimum ampacity considers both the maximum permissible current and the potential impact of voltage drop over the length of the tap. Using a conductor rated below this minimum could result in overheating and safety hazards. Therefore, choosing 33.3 amperes reflects a proper understanding of electrical standards and safety protocols required for tap conductors.