Renewable Energy — Texas Master Practice Questions

6 questions · 3% of the Calculations exam

Worked questions

1. A commercial solar thermal system has a collector area of 100 ft² and a flow rate of 2 gpm. The system is designed to heat water to 120°F. What is the minimum size of the pump required, according to Article 490.21(B) of the 2026 NEC?

A1/2 HP
3/4 HP
C1 HP
D1.5 HP

Exam tip

Always check the manufacturer's specifications for pump requirements.

Why B is correct

Article 490.21(B) requires that the pump size be calculated based on the collector area and flow rate. The calculation for the pump size is typically based on the manufacturer's recommendations or specific formulas, but for this example, 3/4 HP is the standard size for a system with these specifications.

2. A residential geothermal heat pump system has a total of 4 ground loops, each with a length of 100 ft. The loops are buried at a depth of 6 ft. What is the minimum size of the ground loop conductor required, according to Article 490.21(B) of the 2026 NEC?

A10 AWG
8 AWG
C6 AWG
D4 AWG

Exam tip

Always check the manufacturer's specifications for ground loop conductor requirements.

Why B is correct

Article 490.21(B) requires that the ground loop conductor size be calculated based on the loop length and burial depth. The standard size for a loop with these specifications is 8 AWG.

3. A residential photovoltaic (PV) system has a total of 100 PV modules, each with a rated power of 300 W. The inverter has a rated input power of 80 kW. What is the minimum conductor size required for the PV array output, according to Article 690.61(A)(1) of the 2026 NEC?

A10 AWG
B8 AWG
6 AWG
D4 AWG

Exam tip

Always refer to the specific NEC tables for conductor sizing based on current requirements.

Why C is correct

According to Article 690.61(A)(1), the conductor size for the PV array output must be sized to carry the maximum current expected, which is the inverter's rated input power divided by the module's rated power. The calculation is 80,000 W / 300 W/module = 266.67 A. Using Table 310.16, the minimum conductor size for 266.67 A is 6 AWG.

4. A small-scale hydropower system has a generator with a rated output of 50 kW and a rated voltage of 480 V. The system is designed to operate at a head of 20 ft. What is the minimum conductor size required for the generator to the transformer, according to Article 690.61(A)(1) of the 2026 NEC?

A10 AWG
B8 AWG
6 AWG
D4 AWG

Exam tip

Always refer to the specific NEC tables for conductor sizing based on current requirements.

Why C is correct

According to Article 690.61(A)(1), the conductor size must be sized to carry the maximum current expected, which is the rated output divided by the rated voltage. The calculation is 50,000 W / 480 V = 104.17 A. Using Table 310.16, the minimum conductor size for 104.17 A is 6 AWG.

5. A utility-scale wind farm has 100 turbines, each with a rated power of 2 MW. The turbines are interconnected to a substation through a 34.5 kV transmission line. What is the minimum conductor size required for the transmission line, according to Article 694.63(A) of the 2026 NEC?

A500 kcmil
B750 kcmil
1000 kcmil
D1250 kcmil

Exam tip

Always refer to the specific NEC tables for conductor sizing based on current requirements.

Why C is correct

Article 694.63(A) requires that the conductor size be sized to carry the maximum current expected, which is the total rated power of the turbines divided by the voltage. The calculation is 200,000 kW / 34.5 kV = 5,782.05 A. Using Table 310.16, the minimum conductor size for 5,782.05 A is 1000 kcmil.

6. A wind turbine generator has a rated power of 10 kW and a rated wind speed of 25 mph. The turbine is installed at a height of 100 ft. What is the minimum conductor size required for the turbine to the inverter, according to Article 694.63(A) of the 2026 NEC?

A10 AWG
8 AWG
C6 AWG
D4 AWG

Exam tip

Always refer to the specific NEC tables for conductor sizing based on current requirements.

Why B is correct

Article 694.63(A) requires that the conductor size be sized to carry the maximum current expected, which is the rated power divided by the rated wind speed. The calculation is 10,000 W / 25 mph = 400 A. Using Table 310.16, the minimum conductor size for 400 A is 8 AWG.

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Renewable Energy — Texas Master Practice Questions

Worked questions

1. A commercial solar thermal system has a collector area of 100 ft² and a flow rate of 2 gpm. The system is designed to heat water to 120°F. What is the minimum size of the pump required, according to Article 490.21(B) of the 2026 NEC?

2. A residential geothermal heat pump system has a total of 4 ground loops, each with a length of 100 ft. The loops are buried at a depth of 6 ft. What is the minimum size of the ground loop conductor required, according to Article 490.21(B) of the 2026 NEC?

3. A residential photovoltaic (PV) system has a total of 100 PV modules, each with a rated power of 300 W. The inverter has a rated input power of 80 kW. What is the minimum conductor size required for the PV array output, according to Article 690.61(A)(1) of the 2026 NEC?

4. A small-scale hydropower system has a generator with a rated output of 50 kW and a rated voltage of 480 V. The system is designed to operate at a head of 20 ft. What is the minimum conductor size required for the generator to the transformer, according to Article 690.61(A)(1) of the 2026 NEC?

5. A utility-scale wind farm has 100 turbines, each with a rated power of 2 MW. The turbines are interconnected to a substation through a 34.5 kV transmission line. What is the minimum conductor size required for the transmission line, according to Article 694.63(A) of the 2026 NEC?

6. A wind turbine generator has a rated power of 10 kW and a rated wind speed of 25 mph. The turbine is installed at a height of 100 ft. What is the minimum conductor size required for the turbine to the inverter, according to Article 694.63(A) of the 2026 NEC?

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