Archive for the ‘Questions Asked By Our Customers’ Category

Water Damaged Circuit Breakers

October 12th, 2009 Comments off

1200 Amp Square D Circuit Breaker

Buy 1200 Amp Square D Circuit Breakers

We had a conversation with a maintenance mechanic.  He said he was a carpenter one day and an electrician the next, so he needed a little advice.  He had some plastic circuit breakers that got washed down during clean up and, after they dried off, they looked great.  But he wanted to know if he could still use them or if we could tell if they were okay.  They were small single pole circuit breakers, a couple 200 amp circuit breakers, and one 1200 amp breaker.  We call these molded case circuit breakers, but they are what everyone typically just calls circuit breakers.  They also had some old obsolete bus plugs and some small transformers used for emergencies, that he just threw out.  We told him to also throw out the little breakers and the 200 amp.  Actually we told him to smash them so nobody would be tempted to reuse them.  We have torn apart old and new circuit breakers after water damage and they are nasty inside.  You do not want to reuse them.  Very dangerous…  Even if they worked mechanically, they could easily fail to interrupt load and turn into fireworks.   We told him, if he wanted to, he could send us the 1200 amp breaker and we could take it apart and see if it could reliably be reconditioned.  The chances of that are less than 50%.  The real concern is whether or not the over current trip element in the circuit breaker got wet.  If it did, it is very time consuming to take it apart and restore it to perfect working condition.  And the quality control tests after the repair of a trip device are also time consuming.  Many new circuit breakers have electronics which make reliable reconditioning after water damage almost impossible.  One could do a simple clean up of a water damaged breaker and test it and it may pass all the simple routine tests.  But internal inspection shows immediately that the circuit breaker, especially the circuit breaker trip device, is not reliable.  We have seen water damaged used circuit breakers pass the basic insulation resistance, contact resistance, and over current tests, but fail our own additional special quality control tests. The internal inspection shows them to be in horrible condition.  We find rust, free water, mud, and usually slime.  If you have water damaged circuit breakers, just destroy them so no one thinks they are okay and tries to reuse them.  





Circuit Breaker Trips and UPS Dies

July 21st, 2009 Comments off

MIDWEST was asked by a maintenance foreman “why his computer went off’ even though it was on a UPS when they lost power.  He said they had a brand new circuit breaker trip and within a couple minutes his computer went blank.  His UPS just died the first time he needed it.  When we asked why the new circuit breaker tripped, he just smiled and said “OE.”  OE (Operator Error) usually means “We know why but don’t want to say, so don’t ask any more questions.”  Used, obsolete, General Electric, Westinghouse, Square D, Cutler Hammer, used, obsolete, and even new circuit breakers by any mfg. are not designed to protect you from OE.


We explained that a small UPS on a single computer usually is sized to provide power long enough to “save” whatever you are working on and then “shut down” your computer properly so you don’t lose anything.  The UPS also keeps the computer on if you have a brief outage of a few seconds because of things like a storm or utility switching.  The UPS on my computer will keep the computer and monitor and small light on for 12 minutes.  Yes, we’re Engineers, so we actually tested it. Twelve minutes and 27 seconds, to be precise.  Here’s a big tip!  Plug the monitor into the UPS also.  It is not easy to properly shut your computer off when the monitor is blank.  And if you don’t have an office window, we suggest adding a small desk lamp to the UPS.  But a small UPS on a single computer is not designed to outlast OE.


Larger UPS systems will provide more power or power for a longer time.  In any case, UPS systems are only a temporary source of power to critical equipment or to safety equipment.  Sometimes a UPS is used in conjunction with an automatic transfer switch.  The “Automatic Transfer Switch” (ATS) transfers a circuit or panel of circuit breakers from the normal power source to another power source or generator. When an ATS switches, there is a momentary power loss, so computers will still shut down, unless there is a UPS on the computer to provide power for that fraction of a second it takes the ATS to switch from one circuit to another. 


The maintenance foreman’s UPS worked properly.  He didn’t realize the UPS would provide backup power for only a few minutes.

May 21st, 2009 Comments off

A question asked by one of our customers:


You guys work on circuit breakers all the time.  I have a used circuit breaker.  I don’t know why it was laying around in the shop, but I checked it with a VOM and operated it.  Checks okay and sounds okay.  Is it okay, or is there more to it?  My breaker is a 3 pole 100 amp plastic type circuit breaker.




Yes, there is more to it.  MIDWEST’s tests are (1) Voltage Related, (2) Current Related, and (3) Mechanical Related.  The most serious deficiencies may be current, ie heat, related.  MIDWEST overcurrent tests used and new circuit breakers.  In addition to testing the overcurrent functions and insulation quality, we also test the condition of the contacts, including contact resistance.  Poor breaker contacts can cause overheating and lead to serious damage.