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How to Measure Contact Life Erosion

How to Measure Contact Life Erosion
It is important to know proper contactor maintenance techniques to help optimize the life of your device. Follow along for specific tips and best practices for contactor life erosion monitoring.

Joslyn Clark vacuum contactors are built to withstand some of the harshest environments in the world while providing high reliability and longevity. As robust as they are, Joslyn Clark’s contactors can be assembled/dismantled, checked and maintained without using tools. You will need a standard feeler gauge to check for contact wear in your vacuum contactor.

feeler gauge
Example of a standard feeler gauge

Contact Wear 

Before operating the contactor, a general inspection should be made. Manually check for freedom of movement and general cleanliness, but do not attempt to adjust or reset parts. Joslyn Clark contactors self-adjust throughout their life, eliminating the need to clean arc chutes or reset contacts, and saving cost and labor.
Unlike contactors, power devices such as isolators, fuses, and power stabs require preventative maintenance. Prudent engineers will implement preventative maintenance programs, including checking the vacuum contactor by either a high potential or resistance test. 

Mechanically, the interrupter on Joslyn Clark contactors is very well protected. The risk of failure due to factors such as cracked seals or being hit by a wrench is virtually eliminated. The phase assembly has anti-torque and over-compression features that prevent possible damage to the flexible bellows at any time in the interrupter’s life.
The remaining electrical life can be checked by measuring overtravel. This can be done electrically or mechanically without dismantling or requiring special tools. Before doing so, you must isolate the power supply with a visible disconnect. The interrupters can be checked for dielectric strength using a high-potential test set. A micro-ohmmeter will also provide data on contact resistance. 

Contact Resistance 
Resistance across the terminals should be less than 200 microohms with the switch closed. In this instance, the high potential test should be performed if higher contact resistance values are measured.

High Potential Test
The high potential test should be performed using a 50/60 hertz test set, where the voltage is continuously variable up to 20kV RMS. X-radiation at this level is negligible; however, personnel should not be closer than 6 feet to the tested interrupter. This is to avoid electrical high-voltage shock hazards. Before conducting this test, the contactor should be free of dust and other contaminants.  Connect output leads of the test set across the interrupter terminals with the contactor in the OPEN position. Slowly raise the voltage from zero to 10kV RMS and hold for 15 seconds. During this time, any discharges or test set tripping should be ignored unless reaching the test voltage and holding for a 15-second period becomes impossible. The leakage current should not exceed five milliamps during the test.

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