Archive

Posts Tagged ‘arcing damage’

Image of Circuit Breaker Main and Arcing Contacts

July 9th, 2012 No comments

 

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.

Arc Blast Damaged Westinghouse PC32000 Molded Case Circuit Breaker

December 29th, 2011 9 comments
Arc Damaged Westinghouse PC32000 Circuit Breaker

Arc Damaged Westinghouse PC32000 Circuit Breaker

If you want to see a good picture of a large circuit breaker that has been damaged by an arc blast, look at the pictures with this blog. The breaker was a Westinghouse PC32000 molded case circuit breaker. It was a 2000 amp circuit breaker that failed to interrupt a fault and blasted the inside of the breaker until it actually blew a hole through the side of the circuit breaker frame. If you look closely, you will see where a MIDWESTswitchgear service technician actually stuck a screwdriver through the hole. The close up picture shows the hole and shows the extensive arcing damage to the moveable arcing and main contacts. The phase barriers, arc chutes, pretty much the whole Westinghouse PC32000 circuit breaker, was arc blasted beyond repair. One picture shows the destroyed circuit breaker next to a MIDWEST inventory stock PC32000 circuit breaker. This is a tough Westinghouse molded case circuit breaker. It wouldn’t make any difference whether the breaker was Square D or GE General Electric. If the breaker contacts begin to open, but fail to interrupt the current, arc damage will quickly occur. If the breaker is trying to interrupt fault current, extensive arc damage occurs very fast and will quickly expand into a phase to phase fault with catastrophic destruction. The arcing fault may explode outside the case of the circuit breaker.  This is one of the reasons for wearing protective clothing and following safe work practices when operation circuit breakers. Bad things can happen very fast. Too fast for you to get out of the way.  We suggest being paranoid about safety when working around electrical power equipment.

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

Circuit Breaker Broken Handle, Blasted Contacts

February 23rd, 2011 No comments

 

KD3400 Cutler Hammer Circuit Breaker For Sale

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.