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Many manufacturers claim it is not necessary to test motion on a vacuum circuit breaker. Is this true?


No. Travel measurements are a very valuable tool in circuit breaker analysis. One of the common arguments against measuring motion on vacuum CBs is that the contact stroke is so short that you are better off measuring stroke with a pair of calipers when the breaker is in fully open position compared to fully closed position and you can verify the CB is traveling fast enough from the contact times. If you don’t measure motion you will lose valuable information about how the circuit breaker is behaving and won’t see if there is a large amount of overtravel or rebound. If these parameters are too large it can cause damage to the breaker or miss-operation. These parameters can often be easily adjusted in the field and you may be able to find the tolerances on the nameplate.