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Posts Tagged ‘molded case circuit breaker’

Cutler Hammer Circuit Breaker Trip Indication

April 20th, 2012 1 comment

 

Cutler Hammer LD3450 Molded Case Circuit Breaker with Handle In Trip Position

Cutler Hammer LD3450 Molded Case Circuit Breaker with Handle In Trip Position

MIDWEST gets lots of phone calls from folks desperate for a little technical help. Sometimes they know very little about electrical equipment, circuit breakers for example. These are the most difficult calls because the caller may be putting themselves in harms way and not know it. We could tell them what to do, but unqualified people in the electrical power world need to hear “Hire an electrician, call a qualified person, call an electrical contractor.”  We might tell them to send us a picture of their circuit breaker and we can help them identify it, but get a qualified person to service or replace it. All too frequently the caller wants someone to tell them it is okay to just turn the breaker back on after it has tripped for no known reason. This can be very dangerous and against the code. For example, a maintenance mechanic called about a Cutler Hammer 450 amp molded case circuit breaker. This was a Cutler Hammer Catalog Number LD3450 circuit breaker. The breaker had tripped and one area of lighting in their plant was off.  He was told to “find the problem and turn the breaker back on.” Maintenance mechanics tend to be very resourceful individuals. And that is precisely what makes them dangerous around electrical equipment. They can fix mechanical problems, but most are not qualified around the dangers of electrical problems. In this case he thought the Cutler Hammer breaker was broken because the handle was in the middle and he could not close the breaker. It would have been easy to tell him how to reset the breaker so it would close. He was not overly interested in our requirement to have a qualified person investigate why a 400 amp Cutler Hammer breaker tripped. A lot of power or fault current went somewhere. The recommendation would have been the same for a GE General Electric circuit breaker, or Square D, Siemens, or old Westinghouse circuit breaker.  If the trip handle is in the middle, it tripped for a serious reason.  A qualified person has to investigate why. You can not just throw the power back on. And if you do not know how to reset a Cutler Hammer Series C industrial circuit breaker, you are not qualified.

How Do You Test a Circuit Breaker with Ground Fault Protection

June 2nd, 2011 2 comments

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.

Circuit Breaker Trip Device – Hidden Defect

February 2nd, 2011 Comments off
 
Square D PAL362000 Circuit Breakers For Sale

Square D PAL362000 Circuit Breakers For Sale

MIDWEST asked our Switchgear Engineering Technicians for an example of a molded case circuit breaker that had a hidden defect that could only be found by experienced testing.  We find many used circuit breakers that have defects that can be found by a close visual inspection.  Sometimes the defect may not be obvious but an experienced Engineering Technician knows where to look and would find the problem. In the business of repairing and reconditioning circuit breakers, we find about every possible problem that can occur. Whether we are reconditioning a replacement Westinghouse, General Electric or Siemens circuit breaker, many of the problems are the same. But we also frequently find hidden defects that could only be detected using proper testing.

 

 

For this example, let’s just use a replacement Square D PAL362000 circuit breaker. The breaker was reconditioned, which involved removing the cover to thoroughly inspect and maintain the interior of the Square D circuit breaker. The technician was immediately suspicious because he detected the slight smell of an overheated circuit breaker. Once you get that smell in your nose, you never forget it in the future. Even a small whiff tells you there may be a problem. In this case everything visible was in very good condition. There were no signs of overheating at the contacts or the line or load side breaker terminals. But the contact resistance test results indicated very high resistance on the center pole. A DLRO, digital low resistance ohmmeter, was used to locate the problem. The usual location is either the contacts, the bolted connections to the trip device, or the line or load side terminals or lugs. In this case the defect was inside the trip device. And a close sniff of the trip element confirmed it. MIDWEST performed an additional test, a high current test, to determine the voltage drop and therefore the resistance in the trip device on the center pole. Even though this replacement Square D circuit breaker looked just great, the trip device was defect and had to be replaced.

Removing Cover from an Energized Breaker

November 19th, 2010 Comments off

 

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!