Klein Tools CL220 clamp meter

Under IEC 61010, the category reflects location and transient risk: CAT II for plug-in equipment, CAT III for building wiring and panels, CAT IV for the service entrance and utility supply. The voltage is the working voltage at that category. The lowest-rated part (meter, leads or probe) sets the limit.

This is the highest AC current the meter can read, in amps. Clamp and fork meters measure through the jaws without breaking the circuit; multimeters usually need wiring in series through a fused input with a much lower limit. Choose a range comfortably above the loads you work on.

This is the highest AC voltage the meter can display. It should comfortably exceed what you test, such as 120/240 V US residential or 277/480 V commercial. The measurement range is not the safety rating; check the CAT rating for where the meter may be used.

This is the highest DC voltage the meter can display, relevant to batteries, controls, solar arrays and automotive work. Solar strings can run well above residential voltages, so check the range covers your systems. As with AC, the range is separate from the CAT safety rating.

True-RMS meters read AC correctly even when the waveform is distorted, as it often is on circuits with VFDs, LED drivers, electronic ballasts and power supplies. Average-responding meters are accurate only on clean sine waves and may read high or low otherwise. For modern commercial and HVAC work, True-RMS is generally preferred.

Jaw opening is the largest conductor or bundle the jaws can close around, usually given in inches or millimeters. A wider opening fits large feeders and busbar but can be bulkier in a crowded panel. Clamp one conductor only; clamping a cable with hot and neutral together reads near zero.

Display counts set how many digits the meter can show. A 6,000-count meter reads up to 5999 before changing range, so it shows 240.0 V, while a 2,000-count meter would show 240 V. More counts means finer resolution, not necessarily better accuracy, which is a separate spec.

This lists the cells the meter or tester runs on, such as AA, AAA or 9 V. Common sizes are easy to find on the job. A low battery can cause inaccurate readings on some meters, so replace cells when the low-battery indicator shows.

This is the highest resistance the meter can read, in ohms, kilohms or megohms, covering continuity, heater elements, motor windings and sensors. Always measure resistance with the circuit de-energized. This range is not an insulation test; that needs a dedicated insulation tester (megohmmeter).