The fundamentals of resistance measuring with a multimeter
There are usually three reasons for the air switch to trip. Short circuit, overload and malfunction.
There is no need to measure the short circuit, and there are obvious and even huge sound and light phenomena. For tripping caused by this reason, as long as the cause of the short circuit is eliminated, then check whether the contacts of the air switch are burned by the short circuit current. Disconnect the upper-level power supply, so that the air switch is in an absolutely uncharged state, close the air switch, and use a multimeter to measure the three-phase incoming and outgoing wiring terminals of the switch. If the conduction is good, you can try it with power on. If the phase is missing, needless to say, replace the air switch.
In the air switch with a short circuit, the terminals may be broken down. You can use a megger to measure the insulation resistance between the terminals (you can also use a multimeter with a gear above 20K to measure, and remove the inlets on both sides of the air switch. line and outlet). If you start shaking the watch, the pointer of the watch will deflect to the right quickly, indicating that the interphase insulation of the air switch has been broken down and cannot be used. If the insulation resistance is very large, more than a few megohms, you can try it with electricity.
The procedure of power-on trial is as mentioned above. Disconnect the front power supply, turn on the overhauled air switch, and then turn on the front power switch. If the power supply is normal and there is no abnormal sound and smell, the air switch can continue to be used. .
overload. Overload is one of the causes of frequent tripping of the air switch. If you touch the air switch for overload tripping by hand, you will usually feel that the housing is relatively hot, even hot. This will cause the thermal element inside the air switch to produce a protective action.
Use the AC current range of the multimeter to measure the working current of the air switch. If the working current exceeds the rated current of the air switch and continues to run, you should replace the air switch with a larger level according to the actual working current.
Misoperation. When the incoming and outgoing wires of the air switch are aluminum wires, it is easy to oxidize with the copper terminals of the air switch, causing heat at the terminals. The thermal protection device inside the air switch is deformed by heat and produces a protective action. This is a typical misoperation. This problem can be solved as long as the copper-aluminum terminal is pressed on the aluminum wire and tightly combined with the terminal of the air switch.
