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

Square D MA36500 Circuit Breakers For Sale at www.swgr.com

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.”

MIDWEST Uncategorized circuit breaker, electrical switchgear, GE TJK436400WL, general electric, Molded Case Circuit Breakers. Cutler Hammer HLCG3400, Operating Contacts, Square D MA36500

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

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.  

MIDWEST Uncategorized circuit breaker, Electrical Test Equipment, Maintenance Tool, Newer Circuit Breakers, Oil Filled Power Transformers, old circuit breakers, replace circuit breakers, replacement circuit breakers, Siemens Circuit Breakers, Square D Circuit Breakers, switchgear, Wasp Spray, Westinghouse Circuit Breakers

MIDWEST Uncategorized 200 Amp Circuit Breaker, circuit breaker, Circuit Breaker Maintenance, Cutler Hammer ED3200, GE Breakers, general electric, Siemens Breakers, square d, Trip Device, westinghouse breakers

KD3400 Cutler Hammer Circuit Breaker For Sale

We grabbed another circuit breaker out of one of the junk breaker barrels. This one was a Cutler Hammer KD3400.  Again, at first the breaker looked clean and happy. But it only took a second to realize the operating handle was broken off. It takes a pretty hard blow to break the handle off a Cutler Hammer circuit breaker. Handles can be easily replaced. But further inspection revealed serious carbon residue in the area of the line side terminals. You could wipe it off but if there is enough to be visible on the outside, there is something seriously wrong inside. Most of the screws were still missing from the cover, so a technician had removed the cover for inspection of the interior of the circuit breaker and put the cover back on with only a couple screws. A quick conversation with the technician reveal that the arcing contacts were destroyed on two poles and two main contacts were seriously damaged. There was heat damage to pole pieces and arcing damage to the interior insulating, dielectric, material. This Cutler Hammer KD3400 circuit breaker was trash. The breaker did not need to be tested. It was rejected based solely on the visible damage to the operating mechanism, main contacts, and arcing contacts. Square D, Cutler Hammer, GE General Electric or Siemens circuit breakers, it doesn’t make a difference. When this happens, they all fit into the same junk barrels.

MIDWEST Uncategorized arcing damage, circuit breaker, Circuit Breaker Broken Handle, Cutler Hammer KD3400, GE, general electric, main contacts damaged, Siemens Circuit Breakers, square d

Square D MAL361000 Circuit Breaker For Sale

MIDWEST had a customer call because they had an old Square D MAL361000 and it took forever to trip when they had a serious overload problem. He bet it took 3 minutes. This brought up a common misconception concerning how circuit breakers provide protection. When we provide Hands-On Safety Training, this is one of the items we are sure to cover. First of all, whether Square D circuit breakers, Cutler Hammer circuit breakers, GE General Electric circuit breakers, or Siemens circuit breakers, they are not designed to protect people directly. They are designed to protect connected equipment, yet not nuisance trip due to a non harmful transient event. By protecting equipment, circuit breakers consequentially protect people. His old Square D circuit breaker may have taken over 3 minutes to trip and it may have performed the way it was designed. Breakers have a performance specification called a “Time Current Curve,” TCC. In basic terms, whether Westinghouse circuit breakers or ABB circuit breakers, they do not trip immediately at the trip setting. A 1000 amp circuit breaker does not trip right away at 1000 amps or even 1500 or 2000 amps. As a matter of fact, an old 1000 amp Square D MA circuit breaker may have a trip range of 45 seconds to 340 seconds when overloaded with 3000 amps, 300%.  In basic terms, it should not trip in less the 45 seconds and may take as long as 340 seconds to trip. This may seem crazy but, again, it is designed to protect the equipment connected to it while not nuisance tripping. The same breaker would have an instantaneous setting which would determine at what current value the circuit breaker would trip immediately. But, if that setting is over 300%, ie 3000 amps, the breaker would cook for a long time before tripping.  By that time you can smell the breaker overheating.

MIDWEST Uncategorized 1000 Amp Circuit Breaker, 1000 Amp Square D MA, ABB Breaker, circuit breaker, Cutler Hammer Circuit Breaker, Electrical Safety Training, GE Breakers, Hands-On Safety Training, Siemens Breakers, square d circuit breaker, Square D MAL361000, TCC, Time Current Curve, westinghouse breakers

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.       

MIDWEST Uncategorized air circuit breakers, breaker trip device, circuit breaker, Cutler Hammer Circuit Breakers, Electrical Safety Training Class, Federal Pacific Circuit Breakers, GE Circuit Breakers, General Electric Breakers, ITE Circuit Breakers, Large Over Current Time Delays, Merlin Gerin Circuit Breakers, molded case circuit breakers, Over Current Time Delays, over current trip device, power circuit breakers, Siemens Breakers, Square D Circuit Breakers, thermo-magnetic circuit breaker, westinghouse breakers

Question:  When is a circuit breaker not a circuit breaker?

Answer:   When it doesn’t trip and break the circuit.

This is not just a silly riddle.  It unfortunately is a fact of life.  Circuit breakers, either like the small ones in your home, or large industrial ones as supplied by MIDWEST, usually only trip when presented with an extra heavy load, or a short circuit.  This is great news.

But there is bad news also.  In the case of a poor connection somewhere in the circuit path, or a not-so-short short circuit, a circuit breaker will not trip.  To be specific, the electrical engineers at MIDWEST would say that the first case is a high impedance series circuit, and the second is a low impedance parallel circuit.  Either way, very significant heat can be generated in places where heat can cause a fire.  And because the current flowing can be below the trip value, the circuit breaker will not trip to break the circuit. 

Examples of a high impedance series circuit might be a loose screw on a lug, or poor wire nut connection, or a bad solder joint.  These essentially become an additional series resistive component in the circuit.   

Examples of a low impedance parallel circuit are carbonized arc paths on a printed circuit board, a bare wire brushing up against something it shouldn’t, or the failure of a normal load.  These essentially become an additional parallel resistive component in the circuit.   

All of these conditions can easily result in an electrical fire, or even a catastrophic arc flash.  In an industrial setting, one of the products that MIDWEST offers is arc flash and fire resistant Arc Flash Personal Protective Equipment.  MIDWEST also offers Infrared Scanning and Ultrasonic Scanning Services, which is a great way to locate the troublesome series or parallel faults causing dangerous high temperatures.

It is probably safe to say that most electrical fires can be attributed to a circuit fault with just the right impedance resulting in circuit current that does not trip the circuit breaker or blow a fuse.  Often these faults occur in out of way places such as walls or electrical sockets.   

So, when is a circuit breaker not a circuit breaker?   

Answer:  When the impedance of the circuit is such that the current is less than trip current, and the circuit breaker does not trip to break the circuit.

MIDWEST Uncategorized arc flash, circuit breaker, circuit current, circuit fault, electrical fire, electrical fires, high impedance, high impedance series circuit, infrared scanning, low impedance, low impedance parallel circuit, trip current, ultrasonic scanning

MIDWEST received a call for help lately when a client had a dozen surge suppressor strips (with circuit breakers) virtually start on fire.  The interesting thing about this client was that it was a large metropolitan area’s city hall.  The surge suppressor strips were powering the computers that controlled the jail.  The surge suppressor strips had been in place for 10 years without incident.  All of a sudden, on two different floors, a dozen surge suppressor strips overheated.  The strange part is that the circuit breakers inside them did not trip.  Forensic examination  by MIDWEST revealed that the metal oxide varistors inside had overheated, causing the varistors and printed circuit board to burn up;  these were essentially carbonized.  This carbonized material supported arcing, and generated great quantities of heat.  But why didn’t the internal circuit breaker or any building circuit breaker trip when the arcs occurred?

First, a circuit breaker is an electromechanical device that interrupts a circuit when a large current flows through it.  But it has to be a large current, like three to ten times rated current, depending on the particular circuit breaker‘s curves.  This is the breaker’s trip current; in reality, there are engineering curves and graphs that define a circuit breaker’s exact trip.  For a better description, see “How Circuit Breakers Work” and Wikipedia’s entry on circuit breakers.

Why didn’t the circuit breakers trip?  The answer is that if the resistance of the carbon tracking is high enough to limit the current flow to less than the trip current, then the breaker won’t trip.  And the heat just keeps building up inside the strip, resulting in fire.  Thus circuit breakers are not a cure-all; in general, a circuit breaker will trip when presented with a high current short circuit.  But if the fault impedance is current limiting, the circuit breaker gives no protection.  This current limited situation is the cause of most electrical fires and is highly dangerous.  These can be very elusive. 

But, one great solution to the problem is offered by MIDWEST’S Infrared Thermography Service.  But that is the subject of another blog.

MIDWEST Uncategorized carbon tracking, carbonized, circuit breaker, circuit breaker trip, surge sppressor strips