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Posts Tagged ‘replacement circuit breaker’

Aluminum Feeders Damage Old Circuit Breakers

July 2nd, 2010 Comments off

MIDWEST had a customer that seemed to call us about every 5 to 6 months for a replacement circuit breaker. This went on for about three years, before we noticed the pattern. We recognized it because he started calling the same Engineer.   We asked why he needed so many reconditioned replacement circuit breakers over the past two or three years. It seems their facility was built in the 1970s when copper was so scarce and expensive that many projects were built using aluminum cables.  Unfortunately some installations did not use the correct lugs or failed to install the lugs properly. We were very surprised they didn’t have these problems, or worse, decades ago.  We asked them if they still had a couple of the old damaged circuit breakers laying around.  Could they send us one or more of the old circuit breakers that had been damaged, so we could inspect them and give some recommendations on how to prevent future problems.  Inspection of two of their used circuit breakers that had failed, showed extensive heat and arcing damage at one or more of the load side lugs.  We have seen this type damage many times and it invariably was caused by cables that had become loose inside the lug or lugs that had become loose at the breaker connection.  One of our senior engineers worked in electrical construction during the years aluminum cables were used.  He explained how this could be dangerous and he also was very surprised they didn’t have problems many years ago.  He said a lot of new circuit breakers and MLO, ie main lugs only, panel boards were damaged when the aluminum cable terminations failed in the years after installation. He had one strong recommendation.  Hire an old time electrician who remembers those days and knows from experience what has to be done to correct things.  He said this can be a challenge. But, if they don’t do something, they may lose more than an occasional old circuit breaker. He also said to be extremely careful when installing a replacement circuit breaker. Always turn all the power off, including the feeder into the old power panel or panelboard. Safety first.

Replacement Circuit Breaker Tight but Loose

June 4th, 2010 Comments off

During our annual Thermographic Scan of a large manufacturer’s electrical system, MIDWEST found a serious problem with a new circuit breaker. The middle line side bolted connection was extremely hot. They had recently installed a replacement circuit breaker with a higher interrupting current level in this panelboard.  During their Arc Flash Hazard Analysis they discovered several old circuit breakers that did not have high enough interrupting current rating for their system. So they replaced these circuit breakers.  The replacement circuit breakers had high interrupting ratings and it was a straight forward replacement project. Their electricians were pretty sharp, so they were skeptical of our finding.  On third shift they powered down and checked connections and the electricians informed MIDWEST, in their own emphatic vernacular, that the bolts were tight and maybe MIDWEST was loose.  MIDWEST has run into this breaker problem before.  It doesn’t happen often, but we work with old and new circuit breakers every day, all day.  Here is the work practice one must follow when changing out old circuit breakers.  Always lay out the bolts removed from the old circuit breaker such that you know exactly which bolt came out of which hole. Use identical replacements for each bolt and pay attention to the bolt lengths. Replace the bolts with new bolts of the exact same length.  On their installation, the middle line side bolt was shorter than the other two bolts. The middle bolt was not a through bolt. The bolt hole bottomed out.  They used a bolt that was ¼ inch too long and even when it was properly torque tightened, it still was not a physically tight connection, because the bolt hit bottom before the attached bus was tight. We suspect their torque wrench was called “armstrong,” so we were sure they had tightened it enough. Again, on third shift, they replaced the bolt with the right length and the overheating circuit breaker problem disappeared.  MIDWEST recommends following a simple work practice when installing replacement circuit breakers. Keep track of exactly which bolt went where. Usually it does not make a difference, but one in a hundred does.  This customer was lucky we did an infrared scan shortly after the circuit breaker was replaced.