Circuit Breakers Blog – Expert Safety and Usage Information

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

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.

MIDWEST Uncategorized air circuit breakers, circuit breaker, Cutler Hammer, GE, general electric, High Current Test, Insulated Case Breaker, molded case circuit breakers, Nuisance Trip, Over Current Device, Reset Test, square d, Westinghouse

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.

MIDWEST Uncategorized 1600 Amp Siemens Breaker, air circuit breaker, circuit breaker, Current Transformer, Cutler Hammer, Electronic Overcurrent Devices, Federal Pacific Circuit Breaker, GE, general electric circuit breaker, Ground Fault Protection, High Current Test Sets, molded case circuit breaker, square d circuit breaker, TCC, Test a Circuit Breaker, Test Circuit Breakers, Time Current Curve, Westinghouse Circuit Breaker

MIDWEST had a call from a purchasing agent for a manufacturing plant. He was suppose to purchase a 1200 amp Cutler Hammer circuit breaker that he was told could handle 65,000 amps. All he knew was, he had a

MIDWEST Uncategorized 1200 Amp Circuit Breaker, 65000 amp rating, circuit breakers, Cutler Hammer, Cutler Hammer HND312T33W, electrical equipment, HND312T33W, short circuit, Square D Circuit Breakers

MIDWEST had a customer call and ask if it was okay to remove the cover from an old 400 amp circuit breaker, live. Our Infrared Scan indicated the load side connection was overheating. They wanted to repair it, but didn’t want to turn the power off to the whole panel board. They needed to remove the cover of the circuit breaker to make the repair and thought they could just remove the four screws holding the cover on and carefully remove the cover. We explained politely that they were crazy to try such a thing. This was an old molded case circuit breaker and the arc chutes for this breaker were not fastened in place as they are in some breakers. In addition, the arc dividers were metal and they were held together with an insulated band. On some of these breakers we have to tape the band to hold the arc dividers together or they just fall apart. So the danger would be that you remove the cover with the line side still hot and one of the arc chutes falls out and the metal arc dividers fall apart. It would be almost certain that one of the metal arc dividers would short a stationary contact to a moveable contact and cause a horrific arcing blast, arcing fault.  Depending on the instantaneous, ie fault, setting of the main breaker, the fault might last for seconds and result in tremendous damage to the equipment and expose anyone nearby to serious injury or death from an arc blast. Because the fault is on the line side of the breaker, it wouldn’t take much to create a panel board bus fault. This is a good way to get someone seriously injured or killed and a good way to destroy a whole panel board. To remove the cover off any circuit breaker with the line side hot is a very bad idea. But to remove the cover of some of the older circuit breakers, with the line side hot, is just crazy because of the construction of the breaker. Inside molded case circuit breakers there are other devices that may fall out when you remove the cover. Besides all this, there may be something defective inside the breaker, just waiting there, for the first unfortunate person to take the cover off, and then it falls apart or breaks completely. You could get very unlucky. We call these things incipient failures and they can be some of the most nasty and dangerous defects in electrical equipment, because you are not expecting them. This is true whether it’s a Square D, Cutler Hammer, Westinghouse, GE General Electric, or Siemens circuit breaker or any other breaker manufacturer. Turn the main power off!

MIDWEST Uncategorized 400 amp circuit breaker, arc blast, arc chutes, arc damage, arc dividers, arc flash, Cutler Hammer, energized breaker, GE, general electric, infrared scan, insulated band, load side connection, molded case circuit breaker, old circuit breakers, overheating, panel board bus fault, Siemens, Square D Circuit Breakers, Westinghouse

We read about a disagreement between two bloggers over whether or not infrared scanning, or thermography, was needed if you torque tightened the wire connections to power circuit breaker terminals during routine maintenance.  What occurred to MIDWEST were all the possible deficiencies we find in old, new, and replacement circuit breakers, using infrared scanning, that have nothing to do with whether or not the load terminals were tight.  One of the nasty deficiencies is when the cable lug in an old circuit breaker is very tight, but the lug is overheating because the screw, holding the lug to the breaker output tab, is loose. We’ve seen brand new circuit breakers and replacement circuit breakers fry the load side tab of the breaker so bad that the breaker had to be replaced. This is true for new or old Square D, GE General Electric, Westinghouse, Siemens, Cutler Hammer, ABB, any manufacturer. It has nothing to do with a specific circuit breaker manufacturer.

Sometimes the lug is welded to the tab from the arcing between the lug and tab. There is a very sophisticated test one can perform during a maintenance outage to check for this defect. First, check for voltage at the load and line side of the de-energized circuit breakers. Don’t care that the main breaker is off and all the feeder breakers are open.  Check voltage anyway.  You are checking for something that shouldn’t be, not for something you know should be.  We, rather I, have personal experience with getting my hand blasted because a breaker was back fed. Very bizarre set up, unbelievable, just waiting to injure someone.

After checking for voltage, carefully and gently try to move the conductor coming out of each phase of each circuit breaker.  You are trying to see if the cable is loose in the lug and you are trying to see if the lug is loose, moves or turns, in the circuit breaker. You are not trying to force it to move. Just use enough force to see if it is loose in the circuit breaker. If the lug itself is loose, the cable or cables will need to be removed from the lug; The mounting screw for the lug properly tightened; The cables properly reinstalled; And the cables tightened in the lug. Again, don’t be too forceful. On small breakers, you can always make the lug move. Repeating, you just want to use enough force to see if the lugs for that old obsolete circuit breaker are loose.

If the conductive interface, between the lug and the circuit breaker, is damaged from severe overheating or arcing, the defective circuit breaker may need to be replaced. Sometimes the damaged area can be repaired.  MIDWEST does not recommend replacing power circuit breakers while the switchboard is energized. Be safe. Turn things off. Check for voltage everywhere.

MIDWEST Uncategorized ABB, cable lug, conductive interface, Cutler Hammer, de-energized circuit breakers, defective circuit breaker, GE, general electric, infrared scanning, load terminals, overheating, power circuit breaker, replacement circuit breakers, severe arcing, severe overheating, Siemens, square d, thermographic scan, thermography, tighten wire connections, Westinghouse

Cutler Hammer, a venerable name in breakers, bought out the Westinghouse distribution and controls business unit in 1994. This acquisition included the Westinghouse circuit breaker division. MIDWEST carries many types of Cutler Hammer/Westinghouse breakers. A popular Cutler Hammer breaker is the KDC3250 thermal magnetic breaker. Thermal magnetic refers to the type of over current device of the breaker. The thermal element (heat) is responsible for opening the breaker under an over current (long time) condition. The magnetic part is responsible for opening the breaker in a short circuit (instantaneous) condition.

Our engineering and technical sales staff at MIDWEST gets really excited when the phone rings in anticipation of a breaker question. Our expert staff has many years of experience. They are very happy to help you solve your breaker problem.

For the complete line of Cutler Hammer circuit breakers, give us a call or visit our web site at www.swgr.com. We have a huge inventory of used breakers in stock and ready to go. While you have our representative on the line, ask about our other electrical products we handle.

MIDWEST has been in the beakers service, sales, and testing business since 1977, the same year the Yankees won the World Series pennant for the 21^st time. There is no connection between the two events that we are aware of.

MIDWEST maintains a huge inventory of breakers in stock. Whether you are looking for a new, used, or reconditioned breaker, we would be happy to help you find it.

Our office is open from 7:00am to 6:30pm CST.

MIDWEST General - Circuit Breakers Cutler Hammer, Cutler Hammer Circuit Breaker