Mysterious Breaker Operations

[PWR]

A three year old commercial facility recently began experiencing a problem with molded case breakers opening for no apparent reason. In almost all cases, the breakers open they do not trip! The breakers are all Square D "homeline" (a residential grade) or type QO (a commercial grade) and range in size from 225A two pole to 20A single pole. The problem began happening at random about 10 weeks ago. All breakers are fed from a common 120/240 single phase transformer.

There is considerable evidence that the most likely cause; deliberate human actions, does not explain what is happening. Extensive efforts are underway to find an explanation and I'm not looking for suggestions on how to proceed in that regard. I am asking if anyone has experience with a similar situation.

 

[durf208]

this is a long shot, but what if your wiring run a way that would create a loop around your box. could it be possible that one of your high amp. motors might be going bad and be drawing more amps at higher loads enough to create an electro-magnet,creating sort of a soloniod.?
there is some iron present in breakers.im not sure if the base of the switch is reinforced with steel. but you can pick up a breaker with a magnet. with it not being human, this is the only other thing i can dream up. good luck.

 

[PWR]

Epilogue

There has been no resolution to the problem even though several weeks have passed since an "incident" occurred.

Since my last posting I spoke with an individual who had two Dranetz power monitors connected and they detected nothing as the four main breakers for each business opened at the same time while he stood three feet away. Multiple witnesses have described being directly in front of the one panelboard that gives the most trouble while a few to all of the breakers open at the same time.

The owner ran the building off a generator for a week and no incidents occurred during that week. Since then, it has been put back on the utility service and a little over two weeks have passed without problem.

I certainly will not be surprised if the problem returns.

The fact that these breakers open and do not trip leads me to believe that a satisfactory physical explanation will not be obtained.

 

[telasin13]

Just a thought.The next time one of these breakers do this ,reset it then trip it iether with load and or short.You may find that this is just how that breaker works.I have installed breakers from every manufacturer and sometimes they do trip into the off position.The square d home line breakers have not shown themselves to be of the same quality as the older window flag type.
Just a thought

 

[GOswitch]

use a time delay relay and check the behaviour of any one breaker if not trip then o.k.check ur neutral connection also.

 

[droog]

telasin's got the right answer. Part of it, at least.

Some breakers have NO CENTER POSITION. They trip to OFF, the trip action opens the contacts and resets the mechanism in one continuous move. This is common on miniature circuit breakers, both residential and commerical.

I worked at a Cutler-Hammer plant for some years. Cutler-Hammer bought Westinghouse's breaker business. In the same plant, residential breakers that were originally Westinghouse tripped to a center position. Residential MCBs that were originally from CH tripped to OFF. Some exceptions were available on the CH side, where the breaker tripped to a center position. These breakers represented a small fraction of the original CH branch.

Contact SquareD, they'll let you know if these breakers trip to OFF. By the looks of your case I'm pretty sure the answer will be 'yes'. Maybe you have both types of breakers and see some tripping to the center while others trip to OFF. If so, such a mix-up of product would confuse anyone.

Now, the other question is why they are tripping. Before vibrations, I would actually look for temperature issues. Miniature circuit breakers are very susceptible to ambient temperature. Although I believe SquareD has made some patented innovations that address the problem, it is possible they are still tripping because of high temperature. Look for stuff like:

1. Has the customer load increased sharply in a brief period of time? This would increase heat in electrical rooms.

2. Are the terminals on the breakers tight? Loose connections create unnecessary heat. If no maintenance is ever performed, you could have many terminals that need to be tightened.

3. Have the electrical rooms changed in any way recently? Has ventilation to the room been obstructed?

4. Do the breakers trip during a certain time of the day? Does the sun hit the roof of the room more now than in the past (construction changes)? Or are they tripping due to a rise in customer demand?

5. Are there new loads connected to the panels? The addition of several new circuits will increase the temperature in the panel.

6. Are the breakers old? Old stock could have dirty contacts that would increase the temperature in the breaker. Yet, I find it highly unlikely that a high amount of breakers would start to act in this way at the same time. I would look for general sources of heat in the room, or new circuits.

The upper limit for temperature requirements is set by UL in the Y programme of I forget which standard. MCBs have to work indefinitely without tripping at 40 deg C under 100% of rated current. For practical reasons 'indefinitely' is taken as 1-2 hours. After that most breakers have normalised to an even level somewhere above 40C. Exceed the temperature or the current and you're in uncharted territory.

 

[itsmoked]

Did you say even the 225A breakers were doing this?

 

[davidbeach]

Square D type QO breakers have distinct TRIPPED position and must be moved from TRIPPED to OFF before the can be closed again.

 

[mc5w]

First some questions:

1. Are your lights controlled by means of the circuit breakers instead of with light switches? If somebody is getting enough sunlight they could be cutting the power for the sake of their eyes. He or she could also be someone who never remembers which circuit breaker needs to be turned off and just turns off breakers until they hit the right one.

2. Was anybody hired right before this started happening?

I have been able to demonstrate to myself that vibration alone will trip a QO circuit breaker. Just hold QO115 or QO120 in your hand without anything connected, put the handle in the on position, and shake. Just the right shake will cause the circuit breaker to trip. This will happen to ANY circuit breaker that has a 1/2 to 1 cycle pickup and clear time on short circuits. Even General Electric 15 amp and 20 amp circuit breakers will do this.

How much vibration it will take without tripping depends considerably on the magnetic trip setting for short circuits. For a 15 amps circuit breaker the magnetic trip is around 150 amps and to get a 1/2 to 1 cycle clear time at that current level requires the circuit breaker to be as sensitive as a conventional mousetrap!