Posts Tagged ‘circuit breakers’

Circuit Breakers: We’ve got what you need – All Manufacturer’s

February 23rd, 2015 Comments off

Circuit Breakers: We’ve got what you need.  MIDWEST sells reconditioned, used and new Circuit Breakers.  Call today at 800.803.9256!

All manufacturer’s available – Cutler Hammer, General Electric, ITE, Siemens, Square D, Westinghouse, ABB, Airpax, Allen Bradley, American, ASEA Brown Boveri, Bryat, Bulldog, Challenger, Crouse Hinds, Federal Pacific, Fuji, Gould, Heineman, Kraus Naimer, Merlin Gerin, Milbank, Mitsubishi, Moeller, Murray, National, Sace, Sylvania, Telmand, Thomas and Betts, Trumbull, Tyco, Vois Worth, Wadsworth, Zinsco, etc.

Basics of Circuit Breakers in Layperson Terms

December 4th, 2013 1 comment

Basics of Circuit Breakers in Layperson Terms

Square D KAB36225 Circuit Breaker

Square D KAB36225 Circuit Breaker

TKMA30600WL General Electric Circuit Breaker

TKMA30600WL General Electric Circuit Breaker

Equipment that needs electricity to operate doesn’t know the difference between normal electrical current and dangerous electrical current. Normal electrical current would be the normal load amperes the equipment needs to run. If there is a problem, the equipment might use too much current, which could result in over heating and even melting of the wires to the equipment. When current moves through wires, it causes the wires to get warm, depending on the size of the wires compared to the amount of current. Too much current and things get very unhappy, melt, and even burn down buildings. So a device called a circuit breaker is placed in the circuit such that the current has to go through the breaker. The breaker is selected by its voltage rating and current rating so that it protects the wires and equipment connected to it. It will “trip open” if the current is too much and lasts too long. In addition, if the electrical wires actually touch each other, a short circuit occurs and a massive amount of current can flow through the wires. An electrical arc can take place, causing an explosion and burning of anything nearby, including people. So the breaker also has a current rating at which it will “trip instantly” if there is a short circuit…an electrical arc. This assumes the breaker is sized and rated properly.

How do they actually work? The most basic breakers have two protective functions. The first is “overload protection.” In this case, especially in older breakers, an element inside is heat sensitive. As the current increases, this element heats up and eventually will cause the breaker to trip open, opening the circuit and stopping the flow of current. This internal “thermal overload” device is sized properly by the manufacturer. The second protective function is “short circuit protection,” also called fault current protection. An internal magnetic pickup device, a coil, operates instantly when there is a sudden very high current above a fixed level. So overload and fault protection is provided by a properly voltage rated, current rated, and install breaker.

Far more complicated breakers are available today, using electronic protective components, with many more protective functions, ratings, installation configurations, and interrupting designs. Using these requires professional help. Here is a list to give you some idea of the complexity. Do not use any of this information to make a decision on breaker selection. A lot of very important information is not included here.

HLA3250 Cutler Hammer Circuit Breaker

HLA3250 Cutler Hammer Circuit Breaker

Examples of Specific Breakers
• Square D – KAB36225 – 225 amp and 600 volt
• GE General Electric – TKMA31200 – 1200 amp and 600 volt
• Westinghouse – HLA3400 – 400 amp and 600 volt
• Cutler Hammer – MA36800 – 800 amp and 600 volt

General Types of breakers

• Molded case breakers rated 120 volts to 600 volts and 15 amps to 2000 amps
• Insulated case breakers rated up to 600 volts and 3000 amps
• Low voltage air breakers rated up to 600 volts and 4000 amps
• Medium voltage air breakers
• Medium voltage vacuum breakers
• Medium voltage and high voltage oil breakers
• Medium voltage and high voltage SF6 breakers

MA36800 Square D Circuit Breaker

MA36800 Square D Circuit Breaker

Basic Protective functions

• Ground fault pickup and delay
• Overload pickup and delay
• Short time pickup and delay
• Instantaneous pickup and trip.
• There are modern breakers that have many times the number of functions shown here.

Buzz Words explained
• Thermo Magnetic – Having overload and short circuit protection
• Current Limiting – Stopping current extremely fast, possibly within 1/240 second (1/4 cycle)
• Arc Chute – Part of a breaker that extinguishes the electrical arc caused when current is interrupted
• Interrupting Rating – The maximum amount of current a device can interrupt without failing

More obscure words
• Roller Smith – Very old, heavy breakers that used a tank filled with oil to interrupt current
• Tri-Pac – A basic older Westinghouse breaker with fuses inside to interrupt very high current

This is basic information about circuit breakers. Is should not be used for decision making.

Surge Suppressor Fires, Circuit Breakers, and Varistor Conduction

May 29th, 2013 2 comments

A customer called MIDWEST because some of their surge suppressor strips had caught fire underneath office workers’ desks.

The surge suppressors had integral circuit breakers in them for over current protection. However, despite the smoke and fire, the internal circuit breakers never tripped. The surge suppressors were still supplying power to the workers’ desktop computers.

Carefully taking apart the surge suppressors, MIDWEST discovered that extensive damage had been done inside the strip. The actual electronic component inside the strips that is meant to mitigate high voltage line spikes is called a metal oxide varistor. Most of these had burned up inside the strips. In addition, the heating caused massive damage to the printed circuit boards. The metal oxide varistors had greatly overheated, and both the varistors and the circuit boards had mostly been baked into carbon. This carbon was not a perfect short circuit, but had sufficient impedance to limit the current flow below the 15 amperes of the circuit breakers. But it had sufficient conductivity to generate large amounts of heat inside the strips.

From this and other evidence, MIDWEST determined the varistors had suffered an overvoltage condition, probably twice or three times the normal line voltage of 120 volts. This caused the varistors to conduct slightly, and dissipate power. It is very roughly estimated that the component dissipated between 5 and 20 times its nominal rated power dissipation of one watt, or 5 to 20 watts.

Experience has shown that power dissipations of less than roughly 5 times rated do not cause catastrophic damage. Above 5 times rated, and components begin to release the “magic smoke” that manufacturers seem to build into electrical components. Dissipations over about 20 times rated tend to cause violent disintegration of the component, accompanied by immediate flames, possible arc flash, and most noticeably, a very loud acoustic signature.

The varistors have an estimated 200 – 300 Volts RMS on them; therefore conduction currents were probably between 10 milliamperes to 100 milliamperes. Obviously, the 15 ampere circuit breakers would not trip from this conduction current. The overvoltage and the heating probably lasted several minutes.

It might seem strange to realize that the varistors never experienced any high voltage spikes, which is their usual reason for being. A sufficiently high voltage spike normally causes the varistors to explode with the sound of a gunshot, and vaporized zinc oxide and copper becomes spalled in the area around the varistor. That is, the internal bulk varistor material and copper electrodes vaporize in an arc flash, and deposit themselves in tiny balls on adjoining surfaces.

But no such spalling or deposited material was discovered upon disassembly of the melted plastic housings. Instead, the 5 to 20 watts dissipated in the 1 watt body of the varistor simply cooked itself, and everything around it into carbon. Then the carbon supported current flow.

In such a situation, surge suppressors have resulted in a number of fires throughout the US.

Image of Circuit Breaker Main and Arcing Contacts

July 9th, 2012 Comments off


Circuit Breaker Main and Arcing Contacts with Copper Splatter

Circuit Breaker Main and Arcing Contacts with Copper Splatter

When discussing circuit breakers, we like to have good images to show the difference between the main contacts and the arcing contacts. When a circuit breaker opens, the main contacts should open partially first before the arcing contacts start to open. There should be no arcing damage to the main contacts because the arc interruption takes place between the arcing contacts. This protects the current carrying surfaces of the main contacts so there is minimum contact resistance at the main contacts. Good contact surface means no overheating. For the same reason, when the circuit breaker closes, the arcing contacts close first, suffering any arcing damage. After the arcing contacts are closed, the main contacts close. All this keeps the main contacts in good condition. The arcing contacts are enclosed in something called an arc chute that extends and separates the arc until it is extinguished when the circuit breaker opens. When the arc chutes are contaminated with dirt or high humidity or interrupt very high loads or fault currents, the arc chutes take a beating. Whether you’re talking about Square D circuit breakers, Cutler Hammer circuit breakers, Siemens, Westinghouse or GE General Electric circuit breakers, molded case circuit breakers, power circuit breakers, or medium voltage air circuit breakers, the function of the arc chutes is the same, take a beating to protect the main breakers. The attached image shows the damage to the stationary and movable arcing contacts and to the arc runner that extends into the arc chutes to extend and divide the arc until it is extinguished. The main contacts, the 16 curved segments across the middle of the image, are in good shape. No arcing damage what so ever. This image is from a medium voltage air circuit breaker.

Seeing Is Not Believing – Barrels of Junk Circuit Breakers

March 12th, 2012 Comments off
Barrel of Scrap Circuit Breakers

Barrel of Scrap Circuit Breakers

This is another blog on MIDWEST’s barrels of junk circuit breakers. More specifically it is about the difficulty of not believing something you can’t see. This human factor can frequently be a challenge in our world when a customer has a perfectly good looking circuit breaker and we tell them it is no good and they need a replacement circuit breaker that will cost $3500.00. They understand the words, but their emotional pocket book says “But it looks okay.” Even after being presented with the test results or pictures of the inside of the breaker that reveal the deficiency or damage, they find it hard to believe what their brain is telling them isn’t true, “Because it looks okay.” In our world of reconditioning circuit breakers and remanufacturing circuit breakers, we frequently scrap out equipment that looks in perfectly good condition. Usually the reason for tossing out, say a Square D NA361200circuit breaker, involves deficiencies that can not

Square D NA361200 Circuit Breaker

Square D NA361200 Circuit Breaker

be seen physically, unless you remove the cover or thoroughly test the circuit breaker. Whether a reconditioned GE General Electric, Square D, Cutler Hammer or Siemens circuit breaker, if the inspection or test results say junk, out it goes. And keep in mind, some circuit breakers are not built to be happy if you remove the cover. You need to know what you’re doing. Recently we had an electrical contractor stop to pick up several reconditioned Cutler Hammer circuit breakers. He walked by the barrels labeled “Scrap Breakers” and he looked like he saw a little gold mine. He really didn’t like the idea that all those breakers were actually junk and were being scrapped. The contractor in him told him these breakers were worth a fortune. Even after showing him some of the new looking circuit breakers that had the covers off revealing visible deficiencies, all he could say was a skeptical “Hmmm.”  Even we sometimes grunt a little “Hmmm” when we toss out a $3000.00 piece of junk.

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.

Circuit Breaker Arc Chute Missing – Remove the Cover

April 4th, 2011 Comments off

MIDWEST has its own internal blogosphere that especially hums away when something unusual happens, like when one of the Engineers or Engineering Technician discovers something important or rare or both with the electrical equipment they are working on. Here is an example of some internal buzz that also proved the

MA31000 Square D Circuit Breakers For Sale

MA31000 Square D Circuit Breakers For Sale

importance of removing the covers from electrical power circuit breakers, whether Square D circuit breakers, Cutler Hammer circuit breakers or GE General Electric circuit breakers. The need is not related to the manufacturer. In this example, the Engineering Technician was reconditioning and testing a 1000 amp Square D circuit breaker. When he removed the cover of the circuit breaker, he was amazed to find the center pole arc chute was gone. Completely missing. Fortunately the arcing and main contacts appeared undamaged. There was some arcing marks on the arcing contacts, but nothing serious. One could do high current tests, contact resistance tests, and insulation resistance tests and never catch this defect. But the first time this breaker tried to interrupt a large fault current, it could have failed, with the resulting arcing causing an eventual phase to phase arcing fault on the line side of a large circuit breaker. This arcing fault might not be large enough to trip the main breaker immediately. If for some reason the panel board was a MLO, main lugs only, the protective device might be the main breaker or fused switch on the line side of an upstream transformer. This is a worst case environment, but it does happen. It is especially dangerous because the arcing fault may last several minutes before the main protective device operates. And more scary is the possibility of someone being injured by the fault. This is an incipient failure. Also an insidious failure. It is another example of the reason to properly recondition replacement power circuit breakers. Testing alone is not enough.