Posts Tagged ‘air circuit breakers’

Circuit Breaker Reset Tests

January 11th, 2012 Comments off
1600 Amp General Electric Air Circuit Breaker - Catalog No. AK-2A-50-1

1600 Amp General Electric Air Circuit Breaker – Catalog No. AK-2A-50-1 Available at

A customer called MIDWEST to ask why we did something called a “Reset Test” on his circuit breaker. He said he has had circuit breakers tested by switchgear service companies for nearly 30 years and never ever saw something called a circuit breaker “Reset Test.” He has Square D circuit breakers, Westinghouse circuit breakers, General Electrical circuit breakers and newer Cutler Hammer circuit breakers. He checked some of his old test reports and found no “reset tests.”  He had never used MIDWEST before, so he was pretty interested when we explained the reason and procedure for the reset test. The reason was a very pleasant surprise because it gave him greater confidence in the proper performance of his circuit breakers.  MIDWEST started using the circuit breaker “reset test” many years ago. It’s not a standard test procedure. You won’t find it in the text books or instruction manuals. You will find it in MIDWEST’s Training Manual under ‘Scars,’ meaning experience. It’s a carry over procedure from testing old dashpot type air circuit breakers and insulated case circuit breakers and molded case circuit breakers. The reason for the test is that occasionally, seldom but occasionally, a circuit breaker will nuisance trip when put back into service after it has been high current tested. For example, a 1600 amp air circuit breaker, after high current testing, might nuisance trip instantly at 500 amps.  Basically the over current device failed during the high current testing. This was far more common with older “non electronic” over current devices. New electronic over current devices are more reliable, but not perfect. Strange things happen. We are not talking about the service technician forgetting to put the settings back to the correct positions. We are talking about an actual defective device. The test only takes moments. In the interest of quality control, the reset test addresses the “consequences of failure” as opposed to the “probability of failure.”

Yes, we are paranoid about safety and quality.

15 Kv Power Circuit Breaker, Perfect Scrap

September 16th, 2011 Comments off

15 KV Vacuum Circuit Breaker

For an Electrical Power Engineer, it may seem strange to see someone tearing apart a 15 Kv GE magna blast circuit breaker for scrap. They are one of many work horse high voltage air circuit breakers used successfully for decades in manufacturing plants across the Country. But they have been replaced with 15 kv vacuum circuit breakers. Vacuum breakers are reliable, fast acting, low maintenance devices. Many air circuit breakers have been retrofitted with vacuum circuit breakers. The old air circuit breakers are being scrapped because there are just so many on the secondary market and many are not in good condition. They might look great, be in good mechanical condition, but the arc chutes may have serious damage or dielectric deterioration. These things are not noticeable to most people, but MIDWEST tests high voltage circuit breakers and looks can be extremely deceiving. In addition, the cost to recondition an air circuit breaker is very high. It’s not just the mechanics of the circuit breaker, but the dielectrics can be far more costly. The old GE General Electric and Westinghouse high voltage air circuit breakers are everywhere in the secondary market and they sit for years on the storage shelves. If we have 40 GE General Electric 1200 amp magna blast circuit breakers and we sell 5 a year and we can buy as many more as we need, at little cost, then their value today may be greatest as scrap.  This is especially true with the value of scrap metal, like copper, being so high. It’s not 1970 any more.  

Draw Out Air Circuit Breaker Lubrication Problem

April 20th, 2011 Comments off


DS-420 Westinghouse Low Voltage Air Circuit Breakers For Sale by MIDWEST

DS-420 Westinghouse Low Voltage Air Circuit Breakers For Sale by MIDWEST


The over lubrication of low voltage draw out air circuit breakers drives the MIDWEST Switchgear Shop crazy. Sometimes MIDWEST gets these circuit breakers after the owner’s maintenance folks finally give up trying to permanently fix them. They usually do not have the luxury of time, which we have in the switchgear shop. But they are correct in one sense and it’s that they know most of the problems with air circuit breakers are actually mechanical and not electrical at all. But the solution of choice too often is to spray the mechanical operating mechanism with some aerosol type cleaner and lubricant. Then exercise the breaker, spray a little more lub, until the breaker opens and closes mechanically without a problem. But three months later or six or nine, whenever they actually operate it again, the breaker does not open and close properly. So eventually they get sick of this and send it to MIDWEST’s Switchgear Shop. Our job is to take the operating mechanism apart, clean everything, properly lubricate, and reassemble. Concerning lubrication, it is important to know three things. What lubricant to use. Where to put it. And how much to use. Or, as the shop says, how much not to use. The problem of too much lubricant might seem counter intuitive to some folks, but excessive lubricant collects dust and dirt. The wrong lubricant gets hard. And the wrong lubricant in the wrong amount in the wrong place just about guarantees an eventual problem.  Whether an old Cutler Hammer or Westinghouse 1600 amp DA 50 circuit breaker or an old GE AK-1-50, or more modern air circuit breaker, we find most problems are mechanical and most are caused by OE (ie Operator Error), especially when racking in and out, and by poor maintenance. In the real world one sometimes must get the breaker to operate and back in service as soon as possible.  But don’t confuse the temporary fix for a permanent reliable repair.


Circuit Breaker Large Over Current Time Delays

December 29th, 2010 4 comments

In MIDWEST’s training classes for qualified personnel, there is a segment where we explain the long time delay range within which a Square D 1000 amp circuit breaker should trip due to an overload. This information is received with anything from amazement to skepticism to outright disbelief, even though we show the Square D circuit breaker characteristic trip curve.  The overload time delay information is not restricted to Square D circuit breakers. It’s the same with Cutler Hammer, GE General Electric, Siemens, ITE, Westinghouse, Merlin Gerin, or Federal Pacific circuit breakers.


In our training example we use an old Square D 1000 amp MA type circuit breaker.  If we tested this circuit breaker at 3000 amps, that’s 300%, the minimum to maximum trip range is about 45 seconds to 340 seconds. It might trip in 45 seconds or it might not trip for 340 seconds.  This is an old thermo-magnetic circuit breaker, which typically works by heating a bi-metal in the over current trip device. Many newer breakers use electronic over current devices which have more repeatable overload time delay test results.


The illusion is that these Square D, Cutler Hammer, Westinghouse circuit breakers are designed to directly protect people. They are not. The breakers protect the equipment connected to them and they protect the electrical system. They are designed for the characteristics of the equipment connected, such that connected equipment will not be damaged by an overload or fault. This is a basic limited explanation. So, when you think of molded case circuit breakers, power circuit breakers or air circuit breakers, it’s important to know these breakers don’t just trip right at the breaker trip device rating.