Measurement of loop resistance
Main loop
In order to compare the switchgear and control equipment that have undergone the temperature rise test (type test) with all the same model switchgear and control equipment that have undergone factory tests, the measurement of the main circuit resistance should be carried out.
The voltage drop or resistance between each terminal is measured using direct current. Special considerations should be given to enclosed switchgear and control equipment.
The test current should be any value between 100A and the rated current.
Note: Experience has shown that an increase in the main circuit resistance alone cannot be considered as reliable evidence of faulty contacts or connections. At this point, a larger current (as close as possible to the rated current) should be used to repeat the test.
The DC voltage drop or resistance should be measured once before the temperature rise test in the ambient air temperature where the switchgear and control equipment are located; after the temperature rise test, when the switchgear and control equipment has cooled down to the ambient air temperature, it should be measured again. The difference between the two measured resistance values should not exceed 20%.
The type test report should include the measured values of the DC voltage drop or resistance, as well as the general conditions during the test (current, ambient air temperature, measurement location, etc.).
Auxiliary circuit
Measurement of the resistance values of level 1 and level 2 auxiliary contacts
Connect one sample of each type of 1st and 2nd level auxiliary contacts to the resistive load circuit, then apply a DC power supply with an open-circuit voltage of 6V (with a relative deviation of -15%) to allow a current of 10mA to flow through it. Measure its resistance according to the test 2b of GBT5095.2-1997.
The resistance of the closed auxiliary contacts of level 1 and level 2 should not exceed 50.
Note: The oxidation of the contact material may reduce the effective current-carrying capacity, which may lead to an increase in contact resistance, and even prevent conduction in very low-voltage circuits, while not causing any problems in higher-voltage circuits.
The purpose of this test is to examine the contact performance of the contacts under these low voltage conditions. The evaluation criteria take into account the non-linearity of resistance. The value of 50 is derived from statistical data and has been accepted by the users.
Measurement of the resistance of the third-level auxiliary contact
Connect a sample of the third-level auxiliary contact to the resistive load circuit, then apply a DC power supply with an open-circuit voltage of ≤ 30mV and a current of ≤ 10mA. Measure its resistance according to the positive IEC 61810-7 standard.
Post time: Mar-13-2026