Questions about using a multimeter: whether to cut off the power supply of the device under test
Regarding the use of the megohmmeter, cut off the power supply of the equipment being measured before using the megohmmeter. Cut off the power supply of the equipment being measured before measuring. It is prohibited to measure the insulation resistance of live equipment. Conduct short circuit tests and open circuit tests to check whether the megohmmeter is normal.
The power supply of the equipment under test must be cut off before measurement, and it is prohibited to measure the insulation resistance of live equipment.
1. Before measurement, the power supply of the equipment under test must be cut off and the equipment should be short-circuited and discharged to ground. Measurements are never allowed when the equipment is powered to ensure the safety of people and equipment.
2. For equipment that may induce high-voltage electricity, this possibility must be eliminated before measurement can be carried out.
3. The surface of the object to be measured should be clean to reduce contact resistance and ensure the accuracy of the measurement results.
4. Before measurement, check whether the megohmmeter is in normal working condition, mainly check its "0" and "∞" points. That is, shake the handle to make the generator reach the rated speed. The megohmmeter should point at the "0" position when it is short-circuited, and it should point at the "∞" position when it is open-circuited.
5. The lead of the megohmmeter should be multi-stranded soft wire and should be well insulated.
6. For double-circuit overhead lines and busbars that cannot be completely powered off, when the induced voltage of the circuit under test exceeds 12V, or when a thunderstorm occurs, it is prohibited to measure the overhead lines and the electrical equipment connected to the overhead lines.
7. When using the megohmmeter, it should be placed in a stable and solid place, away from large external current conductors and external magnetic fields. Before using the megohmmeter, a short circuit test and an open circuit test should be performed to check whether the megohmmeter is normal.
Short circuit test (zero point calibration). Short-circuit the line and ground wire, and slowly shake the handle. If you find that the meter needle immediately points to the zero point, stop shaking the handle immediately, indicating that the meter is good and the zero point reading of the meter is correct.
Open circuit test (corrected to infinity). After placing the lines and ground wires separately, gradually accelerate slowly and then quickly, and shake the handle at a speed of about 120 r/min. When the reading of the meter reaches a stable indication at infinity, stop shaking the handle, indicating that there is no abnormality in the open circuit test of the meter.
After two steps of short-circuit test and open-circuit test, it is confirmed that there is no problem with the meter before measurement can be carried out. Otherwise, the megger cannot be used.
