Posts Tagged ‘infrared scan’

100% Rated Square D 2000 Amp Circuit Breaker

December 15th, 2010 No comments

MIDWEST lost a battle with the maintenance dollar.  A manufacturing plant had a 2000 amp Square D circuit breaker that was loaded to over 1800 amps, sometimes hitting 1900.  We detected the heavily loaded breaker during an Infrared Scan of the facility.  This was an old Square D circuit breaker mounted in a tap box feeding a 2000 amp bus duct. The local contractor recommended they just replace the breaker with a 100% rated breaker. He said they could use Square D, Cutler Hammer, or General Electric, whoever was cheapest and would fit. Because of the bus configuration, it only made sense to use the same Square D circuit breaker. The customer bit on the idea that just replacing the old circuit breaker would solve their problem and save them a lot of money. We strongly disagreed. Replacing the circuit breaker would make zero difference, in this case. The old Square D molded case circuit breaker was an 80% rated breaker.  More recent replacement Square D circuit breakers, same frame, model number, current rating, were 100% rated, ie 2000 amps. The 100% rated replacement circuit breaker was specified 100% if it was in an enclosure with a much larger volume than the old breaker. In other words, to achieve the 100% rating, the breaker must be in a much larger enclosure so as to properly dissipate the heat generated from 2000 amps. This all makes sense. But to just replace one breaker, whether GE General Electric, Cutler Hammer, Siemens, or Square D, with a 100% rated breaker and not address the installation requirements to achieve the higher rating can be a waste of dollars.  A quick check of the old and new circuit breaker specifications, will tell what the installation requirements are. This is the technical added value that is often ignored, or just not known, in too many facilities, as experienced personnel disappear.

            This facility decided to replace the circuit breaker, but later transferred load off the bus duct.

Removing Cover from an Energized Breaker

November 19th, 2010 No comments


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!

Replacement Circuit Breaker Tight but Loose

June 4th, 2010 No comments

During our annual Thermographic Scan of a large manufacturer’s electrical system, MIDWEST found a serious problem with a new circuit breaker. The middle line side bolted connection was extremely hot. They had recently installed a replacement circuit breaker with a higher interrupting current level in this panelboard.  During their Arc Flash Hazard Analysis they discovered several old circuit breakers that did not have high enough interrupting current rating for their system. So they replaced these circuit breakers.  The replacement circuit breakers had high interrupting ratings and it was a straight forward replacement project. Their electricians were pretty sharp, so they were skeptical of our finding.  On third shift they powered down and checked connections and the electricians informed MIDWEST, in their own emphatic vernacular, that the bolts were tight and maybe MIDWEST was loose.  MIDWEST has run into this breaker problem before.  It doesn’t happen often, but we work with old and new circuit breakers every day, all day.  Here is the work practice one must follow when changing out old circuit breakers.  Always lay out the bolts removed from the old circuit breaker such that you know exactly which bolt came out of which hole. Use identical replacements for each bolt and pay attention to the bolt lengths. Replace the bolts with new bolts of the exact same length.  On their installation, the middle line side bolt was shorter than the other two bolts. The middle bolt was not a through bolt. The bolt hole bottomed out.  They used a bolt that was ¼ inch too long and even when it was properly torque tightened, it still was not a physically tight connection, because the bolt hit bottom before the attached bus was tight. We suspect their torque wrench was called “armstrong,” so we were sure they had tightened it enough. Again, on third shift, they replaced the bolt with the right length and the overheating circuit breaker problem disappeared.  MIDWEST recommends following a simple work practice when installing replacement circuit breakers. Keep track of exactly which bolt went where. Usually it does not make a difference, but one in a hundred does.  This customer was lucky we did an infrared scan shortly after the circuit breaker was replaced.