How does a multimeter measure current and what precautions are needed?

• A. Measures current by measuring voltage drop across a resistor in parallel.
• B. Measures current by inserting in series; must not exceed fuse rating; use proper range.
• C. Measures magnetic field around conductor.
• D. Non-contact current measurement.

Answer: (B)

Measuring current with a multimeter works by routing the circuit current through a low-value internal shunt resistor. The small voltage drop across that shunt is measured by the meter and converted to an amperage reading, so the meter must be placed in series with the load rather than across it. Because the current flows through the meter, you must choose the correct range and use the proper input jack (mA/µA for small currents or the 10 A port for higher currents). Precautions include never exceeding the fuse rating on the chosen range, since blowing a fuse protects the meter and the circuit but can interrupt power and create a hazard. Always de-energize and open the circuit before connecting, or proceed with caution if live measurement is necessary. Use the correct AC or DC setting for the circuit. Non-contact current measurement, such as with a clamp, is a different method not provided by a standard multimeter.