When using a clamp-on ammeter, how many wires are clamped?

When using a clamp-on ammeter, how many wires are clamped?

• A. 4 wires
• B. 2 wires
• C. 1 wire off the input circuit
• D. 3 wires

Answer: (C)

Clamp-on meters read current from the magnetic field produced by the current in a conductor. To get a meaningful reading, you must clamp around a single conductor, typically the input (supply) wire feeding the circuit. If you enclose more than one conductor in the clamp, the fields from the conductors cancel each other out (since the currents are equal and opposite in the supply and return paths), and you’ll get a false or near-zero reading. So, the correct practice is to clamp around just one wire on the input side of the circuit to measure the current entering it.

Clamp-on meters read current from the magnetic field produced by the current in a conductor. To get a meaningful reading, you must clamp around a single conductor, typically the input (supply) wire feeding the circuit. If you enclose more than one conductor in the clamp, the fields from the conductors cancel each other out (since the currents are equal and opposite in the supply and return paths), and you’ll get a false or near-zero reading. So, the correct practice is to clamp around just one wire on the input side of the circuit to measure the current entering it.