Circuit Breaker Technical Information

A circuit breaker is a switch that automatically interrupts the flow of electrical current when the rated current is exceeded due to an electrical overload or fault.

The single best and most inexpensive service on a molded case circuit breaker is to exercise the breaker when you have the opportunity. Open and close the circuit breaker carefully five times. Does the circuit breaker latch open and close properly? And when you exercise the circuit breaker, listen to the circuit breaker operation. Does the circuit breaker open with a single snapping sound or does the circuit breaker sound like one or more of the three poles opened slower than the first pole to open. When the circuit breaker is closed, do all three poles of the circuit breaker close simultaneously. The circuit breaker should open and close with a single snapping sound. Opening and closing the circuit breaker exercises the circuit breaker operating mechanism. It also “wipes” the contacts of the circuit breaker, lowering the contact resistance of the circuit breaker. When the circuit breaker contacts close, they will rub, ie wipe, slightly together, cleaning the contact surfaces of each pole of the circuit breaker. And while you’re doing this, visually inspect the circuit breaker. If the power is on while you’re exercising the circuit breaker, be careful! Be safety conscious! Use your right hand to operate the circuit breaker. Don’t touch anything else when operating the circuit breaker. Keep your body and face as far away from the circuit breaker as possible. Turn your face away from the circuit breaker when you are exercising it. There should not be any exposed energized circuit breaker parts, bus or cable terminations. If there is, use extreme caution and use the proper personal protective equipment (PPE), per NFPA 70E. Actually, if there are exposed energized parts, you must be able to justify being near them. You must justify not turning the power off to exercise the circuit breakers. This also relates to NFPA 70E. One last caution. If the handle of the molded case circuit breaker is broken, be very careful because the metal stud exposed by the broken handle may actually be energized at full voltage. On some circuit breakers, the metal stud is electrically connected to the center pole and therefore part of the electrical circuit. This can be deadly. So be careful.

Molded case circuit breakers are not intended to be maintained or repaired in the same manner as air circuit breakers or power circuit breakers. Molded case circuit breakers are considered by most people as disposable. And most small molded case circuit breakers should be thrown out if they have been damaged or become wet or been submerged. But the larger molded case circuit breakers can be maintained and repaired after they have become wet. The question is whether the cost to repair a damage circuit breaker is worth it or would you be better off purchasing a replacement breaker. When we repair water, mud, or dust damaged molded case circuit breakers, we put the breakers through a thorough disassembly, maintenance, cleaning, repair, re-assembly, and overcurrent testing procedure. It is particularly difficult to repair the “trip element” of a molded case circuit breaker. You really need to know what you are doing and have the specialized test equipment to proof test the circuit breaker after the repairs are complete. But even if the trip element is not repairable, there can be a huge savings by replacing just the “trip element” of the circuit breaker. Again, these repairs are usually only worthwhile for larger circuit breakers, such as 400 amps and larger.

The parts list from the panel’s original packaging and a copy of the return policy. New looking and shiny can be one of several ways to describe what you later need to get rid of because it does not fit your needs, work the way you thought it should or it was missing a piece or two. Buy a new panel if possible, you can usually feel secure that you have everything the manufacturer provided. Your source can also provide the appropriate type of circuit breakers and any needed accessories. If you can’t, due to price or lead time, then buy reconditioned, tested, used equipment. There are vendors of reconditioned units that can usually fix you up if you let them know all that you are trying to accomplish. Sometimes buying new can carry its own risks: That ‘helpful’ sales associate at your local ‘big box’ home supply store that you lured away from the Painting Supplies aisle or from Sporting Goods, or, you visit the local electrical parts house on a very busy day. They charge a bit more and, if you aren’t careful, they will sell you exactly what you asked for. Settling for an as-is circuit breaker panel from a neighbor, garage sale or well meaning nephew might be just exactly what you need, or broken but repairable or the panel could be junk. What to do? Don’t be discouraged, it is not really that hard. It is recommended that you first, develop a short list of requirements. This will make you better prepared when out shopping for a new or used circuit breaker box. The following is also presented to help you understand what is often called a switch box, power panel, panel board, breaker cabinet, breaker box, circuit breaker box, circuit breaker cabinet, circuit panel, wall panel etc. The possibilities and descriptions are endless. #1 Determine what you want to ‘power up’ in the new or available space. Maybe one large electrical device or machine is the only thing that will require power in the area. In that case you might consider installing a dedicated, new or clean, used, safety switch shut-off, or disconnect instead of installing a circuit breaker panel. You can always install a circuit breaker panel later if the power requirements for that space changes. #2 Determine what type of voltage you need in the new space. We can assume a few things before we continue. You are seeking Alternating Current (AC), 60 HZ (Hertz). This is the common frequency available in the United States. Outside of the US, the frequency might be something other than 60HZ. Another popular frequency is 50HZ. Another possibility is you could be looking for Direct Current (DC) if you have a test facility, want a space to charge forklift batteries or provide power that vintage elevator you just added to your villa. For now we will assume you want AC, 60HZ. #3 Determine the voltage category. Most voltages in facilities can be one of two ‘flavors’; medium voltage (over 600 volts) and low voltage (600 Volts or less). A third ’flavor’, high voltage, usually is reserved for utilities; (69000 Volts and above). It is not uncommon to see all three at some utility facilities. Some industrial facilities can have a mix of the first two ‘flavors.’ Most commercial and residential facilities only have low voltage. For now we will assume you want AC, 60HZ, low voltage. #4 Determine how many phases are required for the AC, 60HZ, low voltage? Two common choices are single phase or three phase. Three phase is usually needed to power big motors, air compressors, air conditioners or other large electrical equipment. Some multifamily apartment buildings are fed, by the utilities, from three phase transformers. The individual units are then fed with single phase that is derived from the incoming three phase voltage. In some factories, the lighting may be single phase that is derived from three phase voltage. For now we will assume you want AC, 60HZ, low voltage, three phase. #5 Determine the exact voltage magnitude. Assuming low voltage, AC, 60HZ, three phase, there are a number of choices: The possibilities include 480, 240 and 208. Another customer requirement is ‘about 220 Volts or 230 volts’. This requires further investigation to see if the need is actually 240 or 208 Volts. There are other voltage requirements, usually involving a machine either destined for or coming from outside of the United States. These include 380 volts, 400 Volts, 575 Volts and 600 Volts. For now we will assume you want AC, 60HZ, low voltage, three phase, 480 Volts. #6 Determine how many wires the service has. There are about three different 480 volt magnitudes you might encounter. They include 480 Volts Delta, three wire, 480Y/277 Volts Wye, 4 wire and 480Y Volts Wye, three wire, (when only the three ‘hot’ wires are extended. There are three 208 voltages; 208Y/120 Volts Wye, four wire, 208Y Volts Wye when only three ‘hot’ wires are extended and 208Volts Delta, 3 three wire. There is 240 Volts Delta, 3 wire. There is also 240 volts Delta, 3 wire, grounded B phase. Those other voltages could be Delta, 3 wire, Wye, 4 wire, or Wye, 3 wire when only three ‘hot’ wires are extended. For now we will assume you want AC, 60HZ, low voltage, three phase, 480Y/277 Volts Wye, 4 wire. #7 Determine if the panel will need to have a Main protective device. The circuit breaker panel might be intended to be the only item served from a protective device in an electrically upstream switch board or panel board. The circuit board might be designed as Main Lug Only, MLO. The upstream protective device can be a circuit breaker, a fused disconnect or a fused position in a switchboard or main panel. The circuit breaker panel might not be designed as MLO but instead have its own Main breaker. In that case, all of the circuit breakers in the circuit breaker cabinet would be selected to coordinate with the integral Main protective device. For now we will assume you want AC, 60HZ, low voltage, three phase, 480Y/277 Volts Wye, 4 wire, Main breaker circuit breaker box. #8 Determine the rating or ‘size’ of the circuit breaker panel. There are two considerations regarding size. The size can refer to the rating which is given in terms of amps. Examples include 100 amp switch box, 225 amp panel, 400 amp panel and 600 amp main panel. The larger the amp rating means it is capable of passing more current or serving more load. The size can also refer to space or how many breakers it can hold. A simple rule of thumb, ‘the more spaces you have the more circuit breakers you can add. Three phase breakers usually require three spaces per circuit breaker. A single pole circuit breaker only requires one space and two pole breakers require two spaces. For now we will assume you want AC, 60HZ, low voltage, three phase, 480Y/277 Volts Wye, 4 wire, 400 Amp, Main breaker circuit breaker box with 42 spaces. With the preceeding questions answered, you are about ready to start shopping. The next question usually goes like this. #9 How do I determine what type of circuit breaker cabinet to buy? This question can be re-phrased to: How hard is it going to be, down the road, to find a replacement or extra circuit breaker when the day comes that I need one? That can be a difficult question to answer. The answer is two-fold. The circuit breakers in the desired size may or may not be available plus cost of these circuit breakers will vary depending how hard they are to find. Today in 2006, General Electric(GE), Siemens, Square D (part of Group Schneider) and Cutler-Hammer, (part of Eaton) are still in business. There is a greater chance of locating a breaker in the future if they are currently available from the manufacturer. As customers replace circuit breakers with different sized units, these take-out units find their way to the secondary market and become available for usually less than the price of new. The risk is when these circuit breakers become scarce or when the original manufacturer stops production. Then these take-outs become antiques and the prices start to rise. Usually the circuit breakers of one manufacturer were designed to fit in only the circuit breaker panels of that manufacturer so as to keep a captive audience. Competitors would occasionally develop a compatible replacement to attempt to gain market share. There are situations where one manufacturer produced a ‘near clone’ of a competitors circuit breaker and on the secondary market these ‘clones’ can be more readily available than the original. This can be an issue when looking at new panels from a local home supply retailer. It might be very hard to obtain circuit breakers for a brand new ‘off’ brand circuit panel, many years down the road. It would be advantageous to buy all of the available circuit breakers at the time of the actual panel purchase, today, to avoid problems finding spares or replacement later. A good bet is to stick with the current brands from companies that are still in business. For now we will assume you want AC, 60HZ, low voltage, three phase, 480Y/277 Volts Wye, 4 wire, 400 Amp, Main breaker circuit breaker box with 42 spaces from a manufacturer still in business. Now you are ready to shop for that clean, used bargain. If you know the ultimate configuration for a given space, then your shopping list is complete. All that has been mentioned above assumes that the voltage being used to energize the new space is currently available somewhere else within the building. If this is not the case, then you might be in need of a transformer. This would be covered elsewhere on our web site.