In the indoor installation described, the smallest wires that can be connected to the transformer primary are which size?

In the indoor installation described, the smallest wires that can be connected to the transformer primary are which size?

• A. 300 kcmil
• B. 2/0 kcmil
• C. 3/0 kcmil
• D. 250 kcmil

Answer: (C)

Conductor ampacity must meet the transformer's primary current, with an allowance (usually 125%) for continuous or startup loading, per NEC guidelines. To choose the wire, you first determine the primary current from the transformer's rating and primary voltage, apply the 1.25 multiplier, and then pick the smallest conductor size that has an ampacity at or above that value using the applicable temperature rating. Among the given options, the 3/0 kcmil conductor is the smallest size that meets the required ampacity for the transformer primary in this indoor installation. The larger sizes would work but are not as economical, and the smaller size would be undersized for the current.

Conductor ampacity must meet the transformer's primary current, with an allowance (usually 125%) for continuous or startup loading, per NEC guidelines. To choose the wire, you first determine the primary current from the transformer's rating and primary voltage, apply the 1.25 multiplier, and then pick the smallest conductor size that has an ampacity at or above that value using the applicable temperature rating. Among the given options, the 3/0 kcmil conductor is the smallest size that meets the required ampacity for the transformer primary in this indoor installation. The larger sizes would work but are not as economical, and the smaller size would be undersized for the current.