Archive for the ‘Uncategorized’ Category

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.

Arc Blast Damaged Westinghouse PC32000 Molded Case Circuit Breaker

December 29th, 2011 9 comments
Arc Damaged Westinghouse PC32000 Circuit Breaker

Arc Damaged Westinghouse PC32000 Circuit Breaker

If you want to see a good picture of a large circuit breaker that has been damaged by an arc blast, look at the pictures with this blog. The breaker was a Westinghouse PC32000 molded case circuit breaker. It was a 2000 amp circuit breaker that failed to interrupt a fault and blasted the inside of the breaker until it actually blew a hole through the side of the circuit breaker frame. If you look closely, you will see where a MIDWESTswitchgear service technician actually stuck a screwdriver through the hole. The close up picture shows the hole and shows the extensive arcing damage to the moveable arcing and main contacts. The phase barriers, arc chutes, pretty much the whole Westinghouse PC32000 circuit breaker, was arc blasted beyond repair. One picture shows the destroyed circuit breaker next to a MIDWEST inventory stock PC32000 circuit breaker. This is a tough Westinghouse molded case circuit breaker. It wouldn’t make any difference whether the breaker was Square D or GE General Electric. If the breaker contacts begin to open, but fail to interrupt the current, arc damage will quickly occur. If the breaker is trying to interrupt fault current, extensive arc damage occurs very fast and will quickly expand into a phase to phase fault with catastrophic destruction. The arcing fault may explode outside the case of the circuit breaker.  This is one of the reasons for wearing protective clothing and following safe work practices when operation circuit breakers. Bad things can happen very fast. Too fast for you to get out of the way.  We suggest being paranoid about safety when working around electrical power equipment.

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

Perfect Square D MA36500 Circuit Breaker an Ornamental Reminder

October 28th, 2011 1 comment
Square D MA36500 Circuit Breakers For Sale at

Square D MA36500 Circuit Breakers For Sale at

On one of MIDWEST’s Switchgear Service Desks is a Square D molded case circuit breaker in mint condition. It just sits there, in a place of honor, as a reminder that appearances may outright lie. It has nothing to do with whether or not the circuit breaker is Square D or a Cutler Hammer HLCG3400 or a GE General Electric TJK436400WL or any other manufacture. It is there as a reminder that you can’t tell the condition of the inside of the breaker, the operating condition, based on the outside appearances. We see breakers that look like junk, but test out perfectly. And, as in this case, we see breakers that look mint and are junk. We used this circuit breaker because it looks like it is in such great condition. Looks great, opening and closing sounds right and feels right.  But, when we removed the cover, the contacts were what we call, and this is a technical term, fried. Moveable and stationary, main and operating contacts were burned, brown, and blasted. The inside of the arc dividers were charred. The breaker was fatally damaged and could not be used. But it looked in mint condition.  This is a great training aid and we kept it just for that reason.  There is a tendency to make technical judgments based on appearances. This is human nature. But is does not apply to the technical world and it certainly does not apply to the electrical switchgear world.  We’ll call this, “Breaker fallacy number one.”

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.  

Noisy Circuit Breaker is a Warning

August 12th, 2011 1 comment
HKD3400F Westinghouse 400 Amp Circuit Breakers For Sale at

HKD3400F Westinghouse 400 Amp Circuit Breakers For Sale at

A contractor called MIDWEST for a little free advice. His customer had a 400 amp molded case circuit breaker. This happened to be a 400 amp Westinghouse circuit breaker, but it could just as well have been Square D or General Electric. He was very worried because his customer’s 400 amp circuit breaker was rattling, making a terrible humming and rattling noise. He had never heard this before and didn’t know if the circuit breaker was going to blow up, fall apart or what. He said this was a very old breaker, 1960s. We recommended he measure the load on the feeder cables from the breaker, but to do this very safely. Measure the current at the load end of the feeder, if possible, not at the circuit breaker. It is not totally unusual for an old circuit breaker to rattle and hum away when the load is near or over the rating of the over current device. When the breaker’s internal over current device is picking up because of the load. It depends on the breaker. The noise might be an indication the over current device is picking up and may trip the circuit breaker if the load doesn’t drop down below pickup soon enough. Either way, it may be a good idea to replace the circuit breaker. Sometimes these breakers will nuisance trip at less than the pickup current level. If possible retrofit the old circuit breaker with a newer replacement model. Sometimes the rattling is from the metal arc dividers in the circuit breaker arc chutes. Either way, it is not a noise you want to hear. Check the load. If that is not the problem, change the circuit breaker. Safely.

How Do You Test a Circuit Breaker with Ground Fault Protection

June 2nd, 2011 2 comments

Over the years MIDWEST has been asked many times how we test circuit breakers that have ground fault protection. High current test sets inject single phase current through one pole, ie phase, of the circuit breaker and the test is timed to see if the breaker trips open within the manufacturer’s specified time, based on the TCC, time current curve.  Whether a GE General Electric circuit breaker, or Cutler Hammer or Square D circuit breaker, molded case circuit breaker or air circuit breaker, the same theory applies to the test procedure. Some electronic overcurrent devices on circuit breakers have a feature allowing you to turn off or defect the ground fault protective function. The manufacturer’s specification sheets should explain this. But, if there is no way to turn off the ground fault protective function on a Westinghouse circuit breaker, for example, a specific test procedure must be followed or the circuit breaker will trip open on ground fault function long before you can put enough current through the breaker to properly test the long time or short time function. Maybe the ground fault pickup range is 100 to 1200 amps and the time delay range is 0.1 to 1.0 seconds.  But your 1600 amp Siemens breaker should be long time tested at 300% or 4800 amps and it will take the breaker 22 seconds to trip at that current level. The procedure is to inject current through one phase, current transformer, and then connect the test set up such that the current returns through a second phase, current transformer, in the opposite direction. The currents will cancel out such that the ground fault pickup sees zero current.  Be sure to test in all three possible combinations. Then each phase is tested for ground fault pickup and delay by just injecting current through that phase. These tests are more time consuming for many molded case circuit breakers.  Always check the manufacturer’s literature if you are not sure how to test a specific circuit breaker. The test requirements may differ between a Federal Pacific circuit breaker and a Westinghouse circuit breaker, for example. But they may also differ between types of circuit breakers by the same manufacturer.  And, of course, always be safe.

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.