1. The voltage wiring circuit is open or poorly connected (the contact resistance is unlimited when the wiring is disconnected). When there is strong electromagnetic interference around the test, such as the bus bar is charged, at this time, the live bus will pass air as a medium, which will interfere with the test The capacitance of the meter. Due to interference, the differential mode voltage of the two voltage test lines appears at both ends of the voltage acquisition line of the loop tester.

If the external interference is large, the loop resistance tester will display a value much larger than the resistance value of the product under test. At this time, if the tester has sufficient field test experience, the test result can be judged to be abnormal and the problem can be solved , Can attract attention and finally get the correct test results. However, if the tester is not experienced, he may misjudge the resistance value of the switching circuit and may use power failure to deal with defects, which will cause unnecessary power generation in the future. Loss; if the interference intensity is not very large, the value displayed by the instrument is only within the qualified resistance range of the circuit breaker. This situation is the same as the result of "bad voltage circuit contact", and may also lead to misjudgment.

2. The voltage wiring circuit is disconnected, the loop resistance tester is turned on, and there is no strong electric field interference at the test site. In this case, because there is basically no differential mode voltage input by the amplifier, the test parameters displayed by the instrument are close to 0; If the tester has sufficient field test experience, it can be determined that the voltage loop test line of the instrument is abnormal. After the abnormality of the voltage loop test line of the instrument is eliminated, the final correct test result can be obtained; otherwise, the tester may be mistaken for a problem and interrupted Testing, replacing or refurbishing the instrument will delay the power-off time and bring unnecessary trouble to the testing work.

3. Poor connection of voltage circuit wiring. In most cases, after long-term operation, the terminal of the circuit breaker will produce an oxide film or oil film on the outer surface of the terminal block. Poor contact may occur, and the voltage test clamp itself must also be A certain contact resistance will seriously affect the test results.