Transformers 200 KVA and smaller with a primary rating of ____ volts and below are rated additive.

• A. 4600
• B. 8660
• C. 120/240
• D. 12470

Answer: (B)

The idea being tested is how transformer windings are phased in banks—whether voltages add in the same direction (additive) or oppose each other (subtractive) when you connect units together. For transformers that are 200 kVA and smaller, and whose primary rating is up to a certain voltage, the windings are designed with additive polarity so that when you connect multiple units in series or in a bank, the voltages sum together without phasing issues. That threshold is 8,660 volts. So, primary ratings of 8,660 volts and below are rated additive, which is why 8,660 volts is the correct fill. Values well above that threshold would not fall under this additive designation, and very low voltages like 120/240 V are not the standard primary rating used for this rule.