Test instruments used on electrical systems must be rated for the circuits and equipment for which they are used.

• A. True
• B. False
• C. Only for AC circuits
• D. Only for DC circuits

Answer: (A)

Using test instruments that are properly rated for the circuits and equipment you’re testing is essential for safety and accuracy. Instruments carry voltage and current limits, insulation ratings, and safety categories that show where they can be used without risk. If you use a meter on a circuit beyond its rating, insulation can break down, arcing can occur, and the instrument or the user can be exposed to shock. The safety category rating (often labeled CAT I through CAT IV) indicates how rugged the instrument is for different parts of the electrical system; higher category ratings are needed for service entrances or distribution panels where transient voltages and fault currents are greater.

Many meters handle both AC and DC, but the key is that their rated capabilities cover the type and level of the circuit you’re measuring. Because of these protections and limits, the statement is true: test instruments must be rated for the circuits and equipment for which they are used.