Archive

Posts Tagged ‘defective circuit breaker’

Circuit Breaker Infrared Scanning Disagreement – Lugs

October 27th, 2010 Comments off

Infrared Scan of a Circuit BreakerWe read about a disagreement between two bloggers over whether or not infrared scanning, or thermography, was needed if you torque tightened the wire connections to power circuit breaker terminals during routine maintenance.  What occurred to MIDWEST were all the possible deficiencies we find in old, new, and replacement circuit breakers, using infrared scanning, that have nothing to do with whether or not the load terminals were tight.  One of the nasty deficiencies is when the cable lug in an old circuit breaker is very tight, but the lug is overheating because the screw, holding the lug to the breaker output tab, is loose. We’ve seen brand new circuit breakers and replacement circuit breakers fry the load side tab of the breaker so bad that the breaker had to be replaced. This is true for new or old Square D, GE General Electric, Westinghouse, Siemens, Cutler Hammer, ABB, any manufacturer. It has nothing to do with a specific circuit breaker manufacturer.

 

Sometimes the lug is welded to the tab from the arcing between the lug and tab. There is a very sophisticated test one can perform during a maintenance outage to check for this defect. First, check for voltage at the load and line side of the de-energized circuit breakers. Don’t care that the main breaker is off and all the feeder breakers are open.  Check voltage anyway.  You are checking for something that shouldn’t be, not for something you know should be.  We, rather I, have personal experience with getting my hand blasted because a breaker was back fed. Very bizarre set up, unbelievable, just waiting to injure someone.

 

After checking for voltage, carefully and gently try to move the conductor coming out of each phase of each circuit breaker.  You are trying to see if the cable is loose in the lug and you are trying to see if the lug is loose, moves or turns, in the circuit breaker. You are not trying to force it to move. Just use enough force to see if it is loose in the circuit breaker. If the lug itself is loose, the cable or cables will need to be removed from the lug; The mounting screw for the lug properly tightened; The cables properly reinstalled; And the cables tightened in the lug. Again, don’t be too forceful. On small breakers, you can always make the lug move. Repeating, you just want to use enough force to see if the lugs for that old obsolete circuit breaker are loose.

 

If the conductive interface, between the lug and the circuit breaker, is damaged from severe overheating or arcing, the defective circuit breaker may need to be replaced. Sometimes the damaged area can be repaired.  MIDWEST does not recommend replacing power circuit breakers while the switchboard is energized. Be safe. Turn things off. Check for voltage everywhere.

Shocking Circuit Breaker with Broken Handles

April 2nd, 2010 Comments off

MIDWEST has seen about every old obsolete circuit breaker there is.  We worry about the dangers of some breakers to those not familiar with circuit breakers. Some of these dangers are not present very often, but when they are, they could be lethal.  Here is a quick example of one such danger with molded case circuit breakers.  These are the plastic looking circuit breakers.  This danger usually occurs with three phase breakers.  The breakers have a plastic like toggle that is pushed up and down to turn a circuit breaker on and off.  Some circuit breakers with this toggle like handle are designed such that there is a metal stud that extends from the breaker into the toggle to give it support.  Occasionally the toggle breaks off leaving a visible metal stud sticking out from the front of the now defective circuit breaker.  This metal stud looks innocent enough.  You might even be tempted to use a tool on the stud to turn the breaker off or on.  Don’t.  On some breakers, the metal stud is actually energized at the full voltage of the middle phase.  That’s right, the metal stud is hot.  Shocking! And if you get between it and ground, you could be killed.  Whether old, new, or obsolete, if you find a breaker with a broker handle and there is an exposed metal stud, have a qualified electrician check it out.  The exposed stud would be hot when the breaker is closed, not when it is open, unless the breaker is back fed.  This is shocking news about some circuit breakers with broken handles.