The zero-phase circuit (zero-phase loop) is a circuit formed when the phase line and the neutral line are connected.

The measurement frequency of the zero-phase loop of the continuity characteristics of the protective conductor and the protective device in the electrical equipment is once every three years, and as part of the acceptance work, the reconstruction and new objects are measured.

According to regulations, zero-phase measurement includes measuring the resistance of all circuits of electrical equipment and calculating the short-circuit currents of all phases of the circuit respectively.

Previously, voltmeters and bridges with resistance boxes were used to measure the resistance of the zero-phase loop. After that, using Ohm's law and a calculator, calculate the calculated value of the short-circuit current. Currently, devices using loop resistance testers (also called contact resistance testers) will automatically perform all necessary calculations. The device's display screen immediately displays data such as the impedance of the zero-phase circuit, power supply voltage, short-circuit current and other numerical parameters of the power supply. The results of measuring the zero-phase loop resistance are stored in the device's memory, which allows these data to be transferred to the computer.

Calculate the working current range of the machine in the case of a short circuit based on these data:

Machine type

The time to install the electromagnetic release,

Rated thermal expansion current,

Allowable shutdown time.

The time current parameter is used to calculate the expected response time of the automatic protection device.

Through the analysis of this table in the test report, the quality of electrical installation work, the quality of installed electrical equipment and switchgear, cables and wires can be determined, and the protection measures can also be determined in the case of a short circuit in the circuit breaker Can work in time.

If the value of this parameter is too high when measuring the resistance of the zero-phase circuit, so that the calculated short-circuit current is close to the value of the response current of the electromagnetic release, the response time of the circuit breaker may be longer than the allowable time. The increase in the zero-phase loop resistance value indicates the need to check the quality of all circuit connections, cables and wires, and the condition of connected equipment and equipment. If the situation does not change after performing the above work, it may be necessary to replace the automatic protection device with another automatic protection device with higher current characteristics, or change the electrical items of the line (divide the line into two or more Branch or use automatic protection devices with lower ratings).

The work result of the loop resistance tester measuring the zero phase makes it possible to evaluate the correct selection of protective automatic equipment and the quality of electrical connections in electrical installations, thereby reducing the risk of electric shock to personnel, the possibility of fire caused by short circuits in electrical components, and damage to electrical equipment The risk is minimized.