To properly use a clamp-on-type ammeter to check current flow, what must be done FIRST?

Correct Answer: Option A — hook the jaws of the instrument around the insulated single conductor

To measure current, the clamp-on ammeter's jaws must be placed around only a single insulated conductor. Clamping around multiple conductors (like a duplex cord) causes their magnetic fields to cancel out, resulting in an incorrect reading of zero.