Posts Tagged ‘replacement circuit breakers’

Disaster Replacement Circuit Breakers

June 25th, 2010 Comments off

An engineer called MIDWEST and asked how he could make sure a replacement for one of his old obsolete circuit breakers was not something out of one of the US disaster areas. He said it was a used replacement circuit breaker, but it looked shiny as new and seemed to operate okay. But he just had a bad feeling. To MIDWEST, that means he knows something he isn’t telling us. Regardless, here’s the short answer to his question. If you are qualified, remove the cover from the circuit breaker. Remove the arc chutes. On old circuit breakers, be careful, because the arc chutes may fall out in a dozen pieces. Remove the lugs.  Carefully remove the trip device.  Be sure not to lose any barriers or arc dividers. Then a close visual inspection must be made to detect any signs of corrosion or contamination on the breaker operating mechanism or inside the circuit breaker trip device or under the current carrying components. If the breaker got wet, corrosion should be easy to spot, but be sure to make a hard focused inspection.  Something more than a cosmetic look. During this process, look for signs that someone else has already tried to recondition the circuit breaker. Just cleaning a used or even a new circuit breaker, after it has been immersed in water, can be nearly impossible. There will be corrosion and dirt, even mud, in areas that are inaccessible. The trip device must be taken apart. MIDWEST has experience repairing old trip devices. It usually just isn’t worth the time. And if you mess with the trip element, there is a whole sequence of over current tests that must be performed afterwards. You can’t take a trip device apart, put it back together, and not completely test the circuit breaker afterwards. So, if you suspect an old, obsolete, or new circuit breaker has been exposed to water or mud, your best decision might be to destroy it and then throw it in the trash. Note, we strongly encourage destruction of any circuit breaker that is defective, so no one tries to reuse it. If you find nothing to indicate the breaker was damaged, then you have to put it all properly back together and test it.   

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. 

Expensive Small Replacement Circuit Breakers

May 28th, 2010 Comments off

How is it possible that a very small replacement circuit breaker, weighing only 2 pounds, would cost over $500 when a large replacement power circuit breaker weighing 200 pounds might be less than $1000?  MIDWEST frequently gets questions similar to this one.  The basic answer is economic supply and demand, the most fundamental law of a market driven economy.  A crude paraphrase would be “If the supply of a product goes down and the demand for the same product goes up, the cost of the product will increase.”  There are more people chasing fewer available goods, or circuit breakers.   In the world of supplying replacement circuit breakers, there are some small breakers that are no longer manufactured and are very rare, very difficult to find in the secondary market of used, reconditioned, and obsolete replacement circuit breakers.  For example, there are small molded case circuit breakers that you can hold between two fingers, but they cost over $500.  These breakers are no longer made. They are fairly common in some manufacturing facilities, but they are just not available. There are very few of them for sale and they are becoming scarce.  This is classic low supply and high demand.  On the other hand, there are large circuit breakers that are so common that they are not worth much more than scrap value.  A zillion of them were made.  Although they are no longer manufactured, they are a “dime a dozen,” so to speak. The supply is so large that it far exceeds the demand.  


The high cost of rare replacement breakers is supported by the fact that they are still far less expensive than replacing an entire power panel.  The high cost may seem unreasonable to someone purchasing an item for the first time. However, human nature would tend to look at the cost of a rare item as being too high, but not think of the cost of an abundant item as being too low.