Refer to the setup where Load #1 will draw 63 amps. The smallest size for the tap conductors between Pull Box 2 and the Fused Disconnect for Load #1 is which AWG?

Refer to the setup where Load #1 will draw 63 amps. The smallest size for the tap conductors between Pull Box 2 and the Fused Disconnect for Load #1 is which AWG?

• A. 4
• B. 6
• C. 2
• D. 3

Answer: (D)

The key idea is that tap conductors must be sized to carry at least the rating of the overcurrent device protecting them, not just the actual load current. In this setup, even though Load #1 will draw 63 amps, the tap between Pull Box 2 and the Fused Disconnect must be able to carry the rating of the fuse protecting that disconnect. If that fuse is rated 100 A, the conductors must have an ampacity of at least 100 A. Among common copper conductors with 75°C insulation, AWG 3 is rated about 100 A, while AWG 4 is about 85 A and AWG 2 is about 115 A. Therefore AWG 3 is the smallest conductor that meets the 100 A requirement. If the fuse rating were different, the required conductor size would change accordingly.

The key idea is that tap conductors must be sized to carry at least the rating of the overcurrent device protecting them, not just the actual load current. In this setup, even though Load #1 will draw 63 amps, the tap between Pull Box 2 and the Fused Disconnect must be able to carry the rating of the fuse protecting that disconnect. If that fuse is rated 100 A, the conductors must have an ampacity of at least 100 A. Among common copper conductors with 75°C insulation, AWG 3 is rated about 100 A, while AWG 4 is about 85 A and AWG 2 is about 115 A. Therefore AWG 3 is the smallest conductor that meets the 100 A requirement. If the fuse rating were different, the required conductor size would change accordingly.