Contactor shank, to see whether the burning contact or burning coil, burning contact may of course be the main circuit current is too large, if the burning coil, is often the control loop this side of the voltage is too high.
Capacity is too small, this is the most important problem to consider, generally according to the pump rated current 1.25 times to put the general election type, if the pump load is relatively high for a long time, you can actually measure the current of the pump, according to the working current one to consider the specifications of the contactor. If the capacity choice is small, of course it will often be bad.
Many small brands of domestic contactors, stealing material, or take small capacity to sell large-capacity. Or some fakes and refurbishments that can hurt you, so if you use a cheap contactor, it's safe to use it by at least doubling the capacity.
Control of the power supply voltage is too high, AC contactor coil voltage is generally 220 volts, pressure resistance often have 250 volts, the general single-phase voltage will rarely exceed this worthwhile, but also do not rule out a three-phase imbalance or poor transformer grounding, causing a phase voltage a certain period of time caused by high, if the always burning control circuit coil, Of course, to consider this issue, you can install some overvoltage protection or constant pressure device to avoid.
Pump workplace is more humid, although the general contactor slower resistance is good, but there is a degree, if the water vapor is flying all over the sky, it is indeed easy to cause corrosion or even short-circuit through insulation and so on. At this time can check whether the contactor installed electrical box seal performance is not good, or modify the position of the control cabinet, after all, wet place, need to consider leakage and safety issues, not just contactor burn problems.
If there is some dust or oil pollution in the pump room, impurities particles and so on, plus water vapor, may enter the contactor's magnetic circuit, causing the contactor closed badly, after a period of use will make a buzzing sound, causing vibration wear contacts, but also easy to shorten the service life.
If the voltage of the control circuit is unstable, or the control contacter coil has another small relay, the relay contact contact is not good, which will cause the control loop voltage fluctuations, resulting in contact or contact contacts in a state of bad binding, causing the contact between the resistance is too large, causing the contactor fever and burn out.
If the pump motor is unbalanced, a phase current is too large, and the contactor selection does not take into account the excess margin, after a period of use will also overheat and burn out.
Mechanical aspects, such as whether the pump itself is stuck and other issues, or motor bearings worn, or the motor rotor hit the ground, the resistance becomes larger and causes the motor current to exceed the rated current.
Problems with high currents can be measured by clamp gauges. Wire should also pay attention to, such as wire head loose, or wire ear corrosion oxidation, no contact good, or air switch has a phase contact aging, will cause contact where the heat, and three-phase imbalance, do not rule out these factors cause contactr life is short.