I'm studying for my C5 Inspection Certificate and am looking for a little clarification. I purchased the Mike Holt study material and came across a question I couldn't answer (and my seasoned colleagues couldn't answer).

One of the questions asks : Ground-fault protection of equipment shall be required for a feeder disconnect if the disconnect is rated _____


So the answer stated in the Answer Key says the answer is "D" and refers you to section 215.10.
215.10 states : Each feeder disconnect rated 1000 amperes or more and installed on solidly grounded wye electrical system of more than 150 volts to ground, but not exceeding 600 volts phase to phase, shall be provided with ground fault protection of equipment in accordance with the provisions of 230.95.

My question is, wouldn't "C" and "D" be correct because they are both above 150V and both smaller than 600V? Am I missing something? Is it impossible for a wye electrical system to be 208v because there are 3 hot legs?

Any help is greatly appreciated. Thank you all.