I am not discussing plants and factories where there is an educated workforce, but the small office buildings, wharehouses, etc... that have millions of 480Y/277V systems.
In these building, we see so many circuit breakers installed that are now aging, without any maintenance, and most likely never having ever been exercised.
As each month/year passes more and more of the type of situations I am discussing enter the fray.
What about circuit breakers/systems like this in regards to operator safety and the possibility that the operator may not even be an electrician?
How about the fact that there are still so many electrical companies out there working on these systems and the time bomb is ticking away, in my opinion becoming more and more of a future/soon to be here big problem. These poor guys have so little training, they do not even understand what it is they should be afraid/have respect for.

Ahh yes - and the plot thickens! Pierre, you hit on what I consider a pretty big problem. People are using NFPA tables, IEEE calculations etc. that are based on device clearing times. It's all academic if the device has never been maintained, exercised and does not open. You are right - too many people have no idea how bad this could be. I heard the next 70E standard addresses device testing.

NFPA70b

You are right NFPA70b covers it but is only a recomendation . One stroke of the pen and it will be law . We are in for a very interesting year .

While the NFPA-70B is a recommendation, OSHA 1910.334 is law.
[color="Red"]"Reclosing circuits after protective device operation." After a circuit is deenergized by a circuit protective device, the circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through replaced fuses is prohibited[/color]
Additionally Circuit breaker manufacturers do recommend maintence on their breakers, which the owner is responsable for, but rarely do....
Additionally does everyone know that per UL489 a Circuit breaker is only good for 2 trips into a fault condition?

Only 2 trips? We have loads of breakers over 30 years old that have tripped dozens of times just fine when there is a short circuit.

Why is it that the above mentioned breakers are tripping so many times??

A few were GFCI breakers that sometimes trip when certain lab equipment (small pump motors) are plugged in. We think it was just an assymetrical starting current problem.

We also had a motor that was giving us fits and tripping the MCP on occasion. We eventually replaced the motor that was quite old The other faults were due to years of poor maintenance of equipment. Faults have become less common in recent years as equipment has been replaced, upgraded, etc. and maintenance practices improved. With all of the various breaker operations, we never had a breaker fail. If a testing practice is to test for X operations, that does not necessarily mean it will fail at X+1 operations which seems to be what is implied with davidr's posting.

By the way Pierre, you are correct about aging facilities. We made many improvements but many facilities are still held together with band aids and duct tape.

A few were GFCI breakers that sometimes trip when certain lab equipment (small pump motors) are plugged in. We think it was just an assymetrical starting current problem.

We also had a motor that was giving us fits and tripping the MCP on occasion. We eventually replaced the motor that was quite old The other faults were due to years of poor maintenance of equipment. Faults have become less common in recent years as equipment has been replaced, upgraded, etc. and maintenance practices improved. With all of the various breaker operations, we never had a breaker fail. If a testing practice is to test for X operations, that does not necessarily mean it will fail at X+1 operations which seems to be what is implied with the original posting.

By the way Pierre, you are correct about aging facilites. This was a classic case. We made many improvements but many facilities are still held together with band aids and duct tape.

The UL testing refers to full fault current that may not be available frquently, if ever on a given spot. It means that UL certifies the breaker to withstand the full fault twice and and that no further tests were performed. It does NOT mean that the third time the breaker is guaranteed to blow up or that it will unable to interrupt the fault current. It simply means that the performance of the breaker outside the posted limits are untested and therefore the performance can not be forecasted.

I would expect that most breakers will trip and clear at least as fast as expected by design and not any slower. Current interupting capability is highly dependent on designed clearing times, and if clearing times were extending, it would have caused a huge impact on all distribution systems, long before arc flash was a concept.

I also believe that the breakers that have tripped "dozens of times" usually weaken their hold and trip prematurely.

(But it does give me pause for concern when I observe an old Molded case breaker siting in the basement of some gradeschool, never exercised since it was installed 50 years prior).

Your "expectations" are contrary to experience. On aging and overused breakers clearing times indeed exceed their design limits for various reasons and becoming one major source of arc-flashes exiting the arc-exhausting components and become arc-flashes.

Having said the above I believe that the majority of arc-flashes are still due to other than equipment trip malfunctioning, such as missing coordination studies resulting in missing protective components or maladjusted protective settings or inadequate protective devices. The arcing faults that I have came across were all of this nature and in many cases the danger was enhanced by fundamental errors on the part of the arc-initiating electricians or the whole incident was initiated by neglecting to follow not just proceduers but basic safety rules.

Your experience differs from mine, I have seen molded case breakers that will no longer hold their rated load due to other abuses. I have never seen a molded case breaker that slowed.

I am familiar with 'traces' conducted to verify medium voltage and low voltage power circuit breaker performance, that might include the sensing circuit and relay calibration, however (!), if clearing times exceed design limits, arc flash exposure is probably the least of your concerns.

I am interested in what you have seen regarding slowing breakers. I've spoken to factory reps from both GE and Cutler Hammer about slowing performance on old breakers. For liability reasons they are reluctant to make absolute statements, but the concensus was that slow performance would throw the system protection scheme out the window: series rating, interupting capability, system protection and system coordination would be compromised with bad effects on property and personnel protection.

What I tried to emphasise that aging breaker performance is unpredictable. The trip can be both slower and quicker. I was not restricting my comments to MCB's but breakers of all kinds.

SIEMENS and EATON has the most extensive testing services throughout the country, but there are other non-affilated testing companies that could be more willing to share their data.

The slowing down usually have to do with mechanical part aging of bound up, hardened grease and springs using their modulus. (I've seen this on AK's)Older, non-digital electrical/electronic trip units also have and unpredictable failure mode can be slow or can be fast. (I've seen this on K-DON's with the combo of mechanical issues).

Purely thermal elements such as overloads and fuses always fail to the "early trip" side of failure.