Question 53 QMED05 - Machinist-Pump Technician

The Correct Answer is C **Why Option C is Correct:** Option C describes the ideal characteristics for a high-quality, safe voltage tester (such as a modern digital multimeter or specialized voltage meter). 1. **High Input Impedance:** A high input impedance (typically 1 MΩ to 10 MΩ for modern meters) is crucial for safety and accuracy. When measuring voltage, the meter is placed in parallel with the circuit. A high input impedance draws minimal current from the circuit being tested. By drawing minimal current, it avoids significantly altering the voltage of the circuit being measured (minimizing the "loading" effect), which ensures accurate results. More importantly, drawing minimal current greatly minimizes the energy available to cause an electric shock if the user accidentally contacts the circuit, thus **minimizing the electric shock hazard**. 2. **Higher Voltage Rating:** The voltage rating of the tester (CAT rating and maximum voltage limit) must always be higher than the maximum voltage expected to be measured. This ensures that the internal components, isolation, and protective circuitry of the meter are rated to withstand and safely interrupt the maximum fault voltage and energy, protecting the user from catastrophic failure or arc flash incidents. A meter rated higher than the circuit is fundamentally associated with safety and high quality. **Why the Other Options Are Incorrect:** * **A) a voltage tester with a low input impedance and a lower voltage rating than any expected measured voltages:** * **Low Input Impedance:** This causes the meter to "load" the circuit, potentially altering the measured voltage (inaccurate readings). While some specific industrial testers (like solenoid testers or meters with a "LoZ" function) intentionally use low impedance to drain phantom voltage, a general-purpose, high-quality safety meter defaults to high impedance. A standard low-impedance meter significantly increases the potential fault current if improperly handled, increasing the shock hazard compared to a high-impedance meter. * **Lower Voltage Rating:** This is highly dangerous and violates safety standards. If the meter's rating is exceeded, it risks internal failure, explosion, and severe injury to the user. * **B) a voltage tester with a low input impedance and a higher voltage rating than any expected measured voltages:** * **Low Input Impedance:** As noted above, low impedance is generally avoided in safety-focused high-quality meters because it increases the current drawn and, therefore, the shock hazard risk compared to high impedance. It also risks inaccurate readings due to circuit loading. * **Higher Voltage Rating:** While good for safety against voltage spikes, the low input impedance makes this option inferior to Option C regarding minimizing the electric shock hazard. * **D) a voltage tester with a high input impedance and a lower voltage rating than any expected measured voltages:** * **High Input Impedance:** This is desirable for accuracy and minimizing the shock hazard. * **Lower Voltage Rating:** This makes the meter unsafe and non-compliant for the intended application, risking catastrophic failure if the expected maximum voltage is applied.