Archive for March, 2011

Overheating 1200 Amp Square D Circuit Breaker – Bus Bolts Bottomed Out

March 31st, 2011 Comments off

Square D 1200 Amp Circuit Breaker - Cat. No. MAL361200 For Sale by MIDWEST

MIDWEST found a seriously overheating 1200 amp Square D circuit breaker during the annual Infrared Scan of a Foundry.  The upper left corner of the newly installed circuit breaker lit up like a light bulb when viewed with Infrared. The foundry third shift electricians tightened all the bus connections to the back of the circuit breaker. They said a couple bolts turned a quarter turn and they exercised the breaker. Rescanning showed no change. They didn’t want us working on the circuit breaker in place, so MIDWEST provided a temporary rental circuit breaker so they could remove the defective Square D circuit breaker for us to repair, if possible. Before testing the circuit breaker in our shop, we inspected it. The technician immediately noticed there were different bolts holding the line and load side breaker bus details. In our famous words, “We’ve seen this before.” Got to love experience. As soon as he removed the bolts he determined the bolts, holding the bus detail in the overheating area of the breaker, were bottoming out before the bus detail was tight. This was a quick fix because no overheating damage had occurred. This was an old Square D molded case circuit breaker. But we have seen the same problem on Westinghouse 2000 amp circuit breakers and less frequently on GE circuit breakers. We have never seen it when the circuit breakers have been installed by the manufacturer. It happens when a breaker has been replaced for some reason. 

Important Circuit Breaker Maintenance Tool – Wasp Spray

March 21st, 2011 1 comment

On a field service project, the customer was amazed at how much equipment we had on the large service vans. Besides the test equipment for old and newer circuit breakers and for oil filled power transformers and switchgear, we had the equipment and tools to maintain the switchgear and make many potential repairs. Plus generators, fuel and lights and much more. The customer asked, kind of as a joke, if we had anything on the trucks that was very important but wasn’t technical. This was a shutdown project where the power was turned off at 5:00 AM and had to be back on by 11:00 AM. A lot of work in six hours, including replacing one of the circuit breakers.


The immediate simultaneous response from two Engineering Technicians was, “Hornet Spray.”  Each truck has at least one can of hornet, actually wasp spray, in a can that will spray a stream 10 to 15 feet. We learned decades ago that it can be painful if you have a short shutdown project and open up the switchgear to access your favorite Square D circuit breakers or Westinghouse circuit breakers or new Siemens circuit breakers and you find the switchgear to be a hotel for a bunch of wasp nests. Hard to find a volunteer to take the bite clearing out wasp nests so you can replace circuit breakers. Instead, a little stream of spray here and there and you’re ready to go. No customer wants their project put at risk because of a few bees, even if they are mad. The bees that is. It’s a magic solution for a non technical problem.  So that’s something non technical but extremely important for an outdoor project to inspect, test and maintain circuit breakers and electrical switchgear. Don’t leave home without it.