Voltage taps on a transformer primary are used when the input voltage is ___ than the rated (or normal) voltage.

• A. less
• B. more
• C. either a or b
• D. neither a nor b

Answer: (C)

Taps on a transformer's primary are there to keep the secondary voltage within spec when the incoming line voltage isn’t exactly at its rated value. They let you change the effective number of turns the line sees, which alters the voltage the secondary will produce.

If the input is lower than nominal, you select a tap that helps raise the secondary voltage back toward its rated value; if the input is higher than nominal, you select a tap that lowers the secondary voltage to prevent overvoltage. In other words, these taps are used whenever the input voltage deviates from the rated voltage—in either direction—so the transformer can regulate its output.