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 lost a battle with the maintenance dollar. A manufacturing plant had a 2000 amp Square D circuit breaker that was loaded to over 1800 amps, sometimes hitting 1900. We detected the heavily loaded breaker during an Infrared Scan of the facility. This was an old Square D circuit breaker mounted in a tap box feeding a 2000 amp bus duct. The local contractor recommended they just replace the breaker with a 100% rated breaker. He said they could use Square D, Cutler Hammer, or General Electric, whoever was cheapest and would fit. Because of the bus configuration, it only made sense to use the same Square D circuit breaker. The customer bit on the idea that just replacing the old circuit breaker would solve their problem and save them a lot of money. We strongly disagreed. Replacing the circuit breaker would make zero difference, in this case. The old Square D molded case circuit breaker was an 80% rated breaker. More recent replacement Square D circuit breakers, same frame, model number, current rating, were 100% rated, ie 2000 amps. The 100% rated replacement circuit breaker was specified 100% if it was in an enclosure with a much larger volume than the old breaker. In other words, to achieve the 100% rating, the breaker must be in a much larger enclosure so as to properly dissipate the heat generated from 2000 amps. This all makes sense. But to just replace one breaker, whether GE General Electric, Cutler Hammer, Siemens, or Square D, with a 100% rated breaker and not address the installation requirements to achieve the higher rating can be a waste of dollars. A quick check of the old and new circuit breaker specifications, will tell what the installation requirements are. This is the technical added value that is often ignored, or just not known, in too many facilities, as experienced personnel disappear.
This facility decided to replace the circuit breaker, but later transferred load off the bus duct.
General Electric Circuit Breakers offers many high quality molded case breakers for your power distribution needs. MIDWEST is your single best source for referencing a General Electric Circuit Breaker. Whether new, used, new surplus, or reconditioned we carry a huge inventory of General Electric Circuit Breakers in our warehouse. Our engineering and technical team gets really excited when the phone rings with a question about a General Electric Circuit Breaker.
Here at MIDWEST, we have been testing and maintaining breakers since 1977. You might say, we know breakers like a mother knows her baby. Along with General Electric Circuit Breaker, we offer many types and sizes of breakers in stock and ready to ship. Whatever breaker problem you may have, we are sure to solve it for you. Our complete line of breakers is online at www.swgr.com.
One quick word about our service: As part of our quality control program, all our breakers are put through a rigorous testing procedure before they are shipped to our customers. This assures our customers the high level of service they have come to know from MIDWEST.
While you have one of our people on the phone ask him about our other electrical products we carry. We handle a complete line of power distribution equipment. Just give us a call and speak to us soon. We still answer the phone with a live body. Our office is open from 7:00am to 6:30pm CDT. Our technical team looks forward to speaking with you.