NETA MTS-2011 Microhm Contact Resistance Measurement
NETA MTS-2011 Microhm Contact Resistance Measurement
(OP)
NETA MTS-2011, Part 7.6.1.1, Section 3.2.3 indicates that the contact resistance, in this case on a molded case circuit breaker, that in absence of manufacturer's data, the standard suggests to investigate the problem if a value deviates from adjacent poles or similar breakers by more than 50% of the lowest value. However, at what point is it considered bad enough for replacement? Generally, the techs operate the breaker 3-4 times prior to taking a final reading. However, when all three poles are reading in the micro-ohm range anyway, and there are not any tripping problems occurring, when is a breaker considered bad? Molded case circuit breakers are not intended to be worked on and usually that type of breaker is considered "a throw-away"?






RE: NETA MTS-2011 Microhm Contact Resistance Measurement
For LV breaker where the contacts are readily available by the removal of the arc chute assemblies, I will remove it it and attemp contact cleaning to bring the values below 60 micro.
For non-accesible contacts and due to time contraints, perhaps a dozen trip/close may bring the numbers closer in line and lower. When that does not work, I work out the I2R losses based on the actual jlosd if known, or based on the breaker rating if unknown. You then have to quantify if ie. 100W, 50W, or even 25W per contact heating effect is detrimental for the respective breaker based upon size/rating, that one is a judgement call.
Else the best you can do is make a note that contact values does note fall eithin NETA guideline of falling within 50% of the lowest. If you are brave enough, make a suggestikn to replace kr repair the breaker.
Welcome to the world of testing.
RE: NETA MTS-2011 Microhm Contact Resistance Measurement
old field guy
RE: NETA MTS-2011 Microhm Contact Resistance Measurement
RE: NETA MTS-2011 Microhm Contact Resistance Measurement