Feeders — Texas Master Practice Questions

Exam tip

Always check the specific requirements for overcurrent protection in the applicable code section.

Why D is correct

The minimum overcurrent protection for a feeder is determined by the maximum demand load. For a 480V, 3-phase system, the maximum demand load is 2000kW / 480V = 4166.67A. According to Article 430.53(A), the minimum overcurrent protection should not be less than 125% of the maximum demand load, which is 125% * 4166.67A = 5210.83A. The nearest standard fuse rating is 200A.

Exam tip

Always refer to the specific code sections for critical loads to ensure proper protection.

Why D is correct

For critical loads in data centers, the minimum overcurrent protection is determined by Article 695.7(A). The minimum overcurrent protection for a 500kW load is 200A, as specified in the code.

Exam tip

Always check the code for specific requirements related to cable installation and routing.

Why D is correct

The minimum temperature rating for a feeder cable is determined by the environment in which it will be installed. According to Article 330.10(A), the minimum temperature rating for a cable in a tunnel with a maximum allowable temperature of 75°C is 105°C.

Exam tip

Always consider the service factor when determining the minimum conductor size.

Why C is correct

The minimum conductor size is determined by the maximum load and the NEC requirements. For lighting fixtures, the ampacity is 1.5A per fixture, and for receptacles, it is 1.5A per outlet. Total load = (30 fixtures * 1.5A) + (20 outlets * 1.5A) = 90A. With a service factor of 0.7, the required ampacity is 90A / 0.7 = 128.57A. The minimum conductor size for 128.57A is 14 AWG according to Table 310.16(B)(16).

Exam tip

Always consider voltage drop when designing and installing feeders to ensure proper operation of electrical equipment.

Why B is correct

The maximum allowable voltage drop for a feeder is determined by Article 220.61(A). For a 120/240V, 3-phase system, the maximum allowable voltage drop is 10% of the nominal voltage.

Exam tip

Always verify the conductor size based on the actual operating conditions and the code requirements.

Why C is correct

The minimum conductor size is determined by the maximum load and the NEC requirements. For a 600V, 3-phase system, the ampacity is 1500kW / 600V = 2500A. With a service factor of 0.85, the required ampacity is 2500A / 0.85 = 2941.18A. The minimum conductor size for 2941.18A is 300kcmil according to Table 310.16(B)(16).