Which instrument can measure current in a circuit without disconnecting any components?

Which instrument can measure current in a circuit without disconnecting any components?

• A. A galvanometer.
• B. An ohmmeter.
• C. A clamp-on meter.
• D. An ammeter inserted in series.

Answer: (C)

Measuring current without disconnecting any parts relies on a noninvasive device that clamps around a single conductor. A clamp-on meter does this by using a jaw that closes around a wire. The current in that wire creates a magnetic field, and the meter detects that field (through a current transformer for AC or a Hall sensor for DC) to produce a reading proportional to the actual current. The circuit itself stays intact, so you can measure live current without opening switches or breaking the path. In contrast, devices that must be placed in series require breaking the circuit and inserting the meter in line, which changes the circuit and can interrupt operation. An ohmmeter is used to test resistance by injecting a small current when power is off, not to measure current in a live circuit. An ammeter inserted in series also requires opening the circuit to place the meter in the current path.

Measuring current without disconnecting any parts relies on a noninvasive device that clamps around a single conductor. A clamp-on meter does this by using a jaw that closes around a wire. The current in that wire creates a magnetic field, and the meter detects that field (through a current transformer for AC or a Hall sensor for DC) to produce a reading proportional to the actual current. The circuit itself stays intact, so you can measure live current without opening switches or breaking the path.

In contrast, devices that must be placed in series require breaking the circuit and inserting the meter in line, which changes the circuit and can interrupt operation. An ohmmeter is used to test resistance by injecting a small current when power is off, not to measure current in a live circuit. An ammeter inserted in series also requires opening the circuit to place the meter in the current path.