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Archive for April, 2010

Knock Out for that Circuit Breaker Panel

April 30th, 2010 Comments off

During an Acceptance Testing procedure on new circuit breakers and electrical switchgear used in a manufacturing plant, we ran into a squabble over a 2 inch hole in the side of a power panel.  This was strange because the cost of a 2” knockout closure is nothing.  It was just a small detail on our checklist. But the owner’s representative was determined to make his point that it was unnecessary because the new and the old circuit breaker panel boards were in a locked room and only electricians and other authorized personnel were allowed to enter.

 

This really wasn’t going to cost anything and usually MIDWEST just tells the electrical contractor about these little things and they take care of them willingly. In this case, the contractor was already off the job and we were just following up on more important details, like several breakers that did not meet the interrupting rating required.

 

When we spoke of code and construction in a “workmanlike manner,” it didn’t seem to make a difference.  When we spoke of rodents or accidental entry of something conductive, we were met with disbelief.   

 

Then MIDWEST politely explained examples of rodents causing electrical failures. And we recounted a tragic accident where two ceiling workers were seriously injured when the fixture wire they were working with, was accidentally extended into an opening in similar electrical equipment, causing a horrible electrical fault on the line side of the protective circuit breaker. At this point there was silence and a simple instruction to just take care of it.  Sometimes the human factor is more difficult to deal with than circuit breakers and switchgear. 

Free 3000 Amp Circuit Breaker

April 23rd, 2010 Comments off

A free 3000 amp circuit breaker! This sounded too good to be true when MIDWEST’s Switchgear Shop made the announcement.  And, of course, they were just being wise guys. It was another opportunity to spin up the Engineers a little, and it worked. What they meant was the breaker was shipped loose on the pallet, in other words free. It seems MIDWEST was shipped an old 3000 amp power circuit breaker for maintenance and testing.  The breaker was properly wrapped, boxed, and strapped to a sturdy piece of plywood.  The plywood was on a sturdy pallet. Looked like someone did a good job shipping this fairly large power circuit breaker. 

 

But, the breaker was free, loose on the pallet, because the plywood was not fastened to the pallet. It could just slid around, slid right off the pallet. We’ve seen a lot of different techniques used to ship old and new circuit breakers. Some good ideas and some bad. In this case, someone went all out, but still missed the mark.  Fortunately there was no damage and we added this information to our training file.

Circuit Breaker Will Not Reclose

April 16th, 2010 Comments off

An all too frequent scenario experienced by customers working in power distribution involves an air circuit breaker which after having tripped open fails to close again. When racked-in and the breaker charged it may trip free when the close button is engaged. 

 

Running down the list of possible factors, there are several key culprits which come to mind. Topping the list is the breaker racking-in interlock mechanism.  This interlock system is designed to ensure the breaker is fully in the racked-in position, the contact fingers fully engaged with the bus contact stabs, before closing.  What often happens is all too typical. The close tolerances designed in the racking-in mechanism can get out of tolerance through use if you so much as breathe on it wrong, or so it may seem. Even out of the gate as new equipment, they can be quite finicky birds requiring some TLC to keep them working smoothly.

 

The fix can be as simple as removing the front cover of the circuit breaker and lubricating the racking mechanism allowing its resets and mechanicals to function properly. The mechanism’s dogs can get stiff preventing the mechanism from seating properly.

 

In other cases we look for evidence the breaker may be over-racked in the racked-in position, throwing the interlock system out of alignment.

 

The circuit breaker proper may be out of alignment in its cell. This is very bad and runs the risk the load side connections (the finger clusters) may not be seated properly on the bus stabs. This is a nightmarish scenario if somehow the breaker manages to close and becomes energized.

 

When part of a good maintenance program, an air circuit breaker can be expected to delivery good reliable service for many years to come.

Square D I-Line Molded Case Breakers

April 9th, 2010 Comments off

What is it about these breakers that people like so much? In a word, simplicity ─ they are quick and easy to work with.

 

Most breakers such as the Cutler Hammer EHD3100, to give one example, use “details” (mounting bus details) to attach the breaker line side to the panel board bus. Details are an additional item at a slightly greater expense and are not necessary for Square D I-Line breakers.  I-Line breakers line side connections are finger clusters which connect directly onto the panel board bus making swapping out an I-line breaker as easy as drinking a cup of coffee in the morning.

 

The process is pretty straight forward:

 

First up, de-energize the panel board and lock out and tag out the switch supplying power to the panel board. Check voltage to make sure the panel board is dead and that it is not being back fed through another source. Remove the panel board dead front. Loosen the load side lugs and remove the load side cables from the breaker. You now have access to the single mounting screw holding the I-Line breaker in place. After removing the mounting screw, place a screw driver in the prying slot on the mounting bracket on the load side of the breaker and pry the breaker horizontally away from the bus running vertically down the center of the panel board. The breaker can now be removed from the panel board. Put the new I-Line breaker in place and using a reverse prying motion, slide the breaker horizontally into position such that the line side finger clusters make complete contact with the bus. Insert the mounting screw and tighten firmly. Do not over tighten this screw as it is a sheet metal screw designed to hold the breaker in position only. Reconnect the load side cables, then go ahead and install the dead front back onto the panel board.

 

At this point it’s always a good idea to exercise the breakers in the panel board, working the action by opening and closing the breakers several times. With the breakers in the off position in the panel board you are now set to power back up.

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.