On supply voltages over 50 Volts the instrument will prevent the test button from performing an insulation test, protecting your instrument from damage.

• A. Will always allow insulation test at any voltage
• B. Is inhibited above 50 volts automatically
• C. True
• D. False

Answer: (C)

The main idea here is that insulation testers include a safety feature that disables the test when the supply voltage is too high. High test voltages can stress or damage the instrument, so many devices automatically inhibit the insulation test if the input voltage exceeds a certain threshold—often around 50 V. This design protects both the instrument and the user from harm while ensuring testing only occurs within the safe operating range. Because of that automatic inhibition above 50 V, the statement is true: the test button won’t perform an insulation test when the supply voltage is over 50 V.