Fairly modern form-2 240V meters work OK at 120V. For socket-based versions—labeled "fm2S"—line goes to top blades, and load goes to bottom blades. Just be sure the neutral connection is not grounded anywhere on the load side, or the meter will underregister. It takes roughly a 30-watt load to get the meter disc turning. The label “Kh” is the number of watthours {not kWh} registered per disc revolution.
