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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!