Which of the following factors affects the capacity of a circuit?

The capacity of a circuit can be significantly influenced by the configuration of the transformer secondaries. This relates to how the secondaries are arranged—whether they are in series or parallel, and how they interact to provide voltage and current to the load.

In a parallel configuration, for example, the voltages across each secondary remain the same, while the overall current capacity increases. Conversely, in a series configuration, the current remains the same, but the voltages add up, which can also affect how much power can be delivered to the load. Therefore, different configurations can directly influence the maximum power output of the transformer and, consequently, the capacity of the circuit.

The other choices address aspects that have varying degrees of impact on circuit capacity, such as the type of transformer and the number of wires. However, the specific arrangement of transformer secondaries is crucial in determining how well the circuit can handle electrical demands.