Circuit Breaker Push/Pull Resetting 1

[Stache]

I was wonder if any of you have had any experience with the push pull circuit breakers. Here is what the FAA wants owner/operators to do annually is to push in each breaker and pull it out. I have no problem with this practice as it may help to clean the contacts, however the question is will it harm the breaker over time.

Past experience tells human nature is if one is good then several times is better. Resetting the circuit breaker many times does it harm the breaker or reduce the life. I have heard it will cause the breaker not to trip as required if it is reset to many times.

Any opinions?

Stache

 

[FieldTeam]

The referenced FAA document makes it clear that circuit breakers not be used as switches. The recommendation is to "periodically cycle circuit breakers on and off", basically to improve voltage drop at rated current. The period would have to be determined. They should have said "pull and reset" so as not to make it sound like you were operating a switch.

Boeing has a service letter titled Circuit Breaker Reliability that references DOT/FAA/AR-01/118 (

http://www.tc.faa.gov/its/worldpac/techrpt/ar01-118.pdf).

Boeing states that they are unable to quantify the benefit or common interval for cycling circuit breakers. Some operators of aging Boeing aircraft have opted to include this recommendation in their C check intervals.

It is common practice where I am to pull select breakers after flight for safety purposes. We have not seen these breakers being replaced more than any others. On the other hand, breakers in circuits where tripping has occured due to component or wiring problems do seem to require replacement more often, especially on the higher amperage rated ones.

 

[Barry1961]

Just from a mechanical design stand point the breaker should be able to be manually reset many more time than it can trip due to an over current. All common thermal overloads have a very limited life in number of trips. Of course they intended only to trip when something fails which should be rare.

I have not seen test data on using breakers for switches but I would guess the L-10 life to be in the ten thousands of cycles while the trip life may be single digit depending on type of overload.

Barry1961

 

[rerig]

I would rather do a "pull then Reset" circuit breaker check manually once a year than to have one pop and not be able to reset it. After all, it is a mechanical device. Might even have corroded contacts and be stuck closed.
I would rather check anything on the ground, than have to figure how to fix it in-flight.
(I once had to get into the E&E compartment in flight, half way to Bermuda, to reseat the transponder. The wise-guy Pilot slid his seat back over the hatch and wouldn't let me out. Had to start disconnecting radios to get his attantion)
(USN C-9B = DC9-32)
Fortunately this could be checked in flight if you had to.

Rerig

 

[EVdave13]

I have a little background info. to offer on this...

The NIAR (National Institute for Aviation Research) at Wichita State U. has been disassembling aged GA aircraft to develop a SSID for them, which hopefully, will reveal areas to look at on older GA aircraft in general in order to prevent fatigue and corrosion problems.

The first hard recommendation they presented to industry and the FAA was this pull and reset recommendation. As you know, a breaker may go it's entire lifetime without having to trip. At least if everything with the circuit operates according to design, it will.

They found that many of the breakers (about half) that were in the aircraft they disassembled did not trip at the listed currents. Over time, the contacts had welded together somewhat (presumably due to corrosion - and I'm sure there were probably electrical consequences within the breaker that held ti back, too, but I don't know anything about those), and the trip mechanism didn't generate enough force to trip the breakers.

They retested the breakers after opening and closing them one time, and most of the discrepant breakers fell back into their operating specification limits, and started tripping at the designed current. After being reset up to three times, all breakers were back to operating within their respective specification limits. Opening and resetting them cleaned off the contacts and freed the mechanisms, and kept them where they were operating freely.

The opening and closing was not done under load. Opening and closing under load causes arcing which damages the contacts a little every time.

 

[kiwisCANfly]

At my work it is routine during overnight maintenance to deactivate the hydraulic system by pulling CB's as required (B737). This means the CB may be cycled up to 100 times/yr. Surely if anything this would cause the CB to trip early as the trip mechanisim would wear prematurely.I've never seen any of them replaced for any reason.