In boiler installations, the copper conductor used between the disconnect and the boiler must be sized using THHN/THWN insulation. Which gauge satisfies the minimum sizing for an 8.2 kW, 240 V, 1-phase boiler?

In boiler installations, the copper conductor used between the disconnect and the boiler must be sized using THHN/THWN insulation. Which gauge satisfies the minimum sizing for an 8.2 kW, 240 V, 1-phase boiler?

• A. 6
• B. 8
• C. 10
• D. 12

Answer: (B)

Sizing the conductor for a boiler branch circuit is about matching the conductor’s ampacity to the current the boiler will draw, using THHN/THWN insulation. First find the load current: 8.2 kW at 240 V for a single-phase boiler draws I = P/V = 8200/240 ≈ 34.2 A. Boilers acting as a continuous load typically require the circuit to be sized at 125% of the load, so 34.2 A × 1.25 ≈ 42.7 A. Then check copper THHN/THWN ampacities. With terminations rated at 75°C (common for modern equipment), 8 AWG copper has about 50 A of ampacity, 6 AWG about 65 A, 10 AWG about 40–50 A depending on the column, and 12 AWG about 25–30 A. The smallest gauge that can safely carry roughly 42.7 A is 8 AWG. Note: if the terminations are only 60°C rated, 8 AWG would have an ampacity around 40 A, which would fall short of the 42.7 A requirement, and you’d need 6 AWG. Under typical 75°C terminations, 8 AWG is the minimum that meets the load.

Sizing the conductor for a boiler branch circuit is about matching the conductor’s ampacity to the current the boiler will draw, using THHN/THWN insulation. First find the load current: 8.2 kW at 240 V for a single-phase boiler draws I = P/V = 8200/240 ≈ 34.2 A. Boilers acting as a continuous load typically require the circuit to be sized at 125% of the load, so 34.2 A × 1.25 ≈ 42.7 A.

Then check copper THHN/THWN ampacities. With terminations rated at 75°C (common for modern equipment), 8 AWG copper has about 50 A of ampacity, 6 AWG about 65 A, 10 AWG about 40–50 A depending on the column, and 12 AWG about 25–30 A. The smallest gauge that can safely carry roughly 42.7 A is 8 AWG.

Note: if the terminations are only 60°C rated, 8 AWG would have an ampacity around 40 A, which would fall short of the 42.7 A requirement, and you’d need 6 AWG. Under typical 75°C terminations, 8 AWG is the minimum that meets the load.