The wire whose current is being measured, should be passed through the centre of the clamp arms i.e. the hole in the middle when the clamp is closed. The "contacts" in the ends of the clamp arms are soft iron pole pieces, that form a magnetic circut rather than an electrical one, and need to be as close to each other as possible, for an accurate reading.
The usefulness of clamp meters is that the circuit, whose current is being measured, doesn't need to be interrupted to make the measurement, nor does the insulation need to be broken through to make the measurement.
The usefulness of clamp meters is that the circuit, whose current is being measured, doesn't need to be interrupted to make the measurement, nor does the insulation need to be broken through to make the measurement.