Old Circuit Breakers

[PT20J]

When I upgraded my panel I kept the original circuit breakers. During testing, I have pulled and reset some more than they probably have ever been exercised in their lifetime.  I started to wonder about whether 25 year-old circuit breakers were still reliable and if I was damaging them by exercising them.

I did some research and it turns out the FAA wondered the same thing and did a study on a sample of circuit breakers removed from old airliners. https://www.tc.faa.gov/its/worldpac/techrpt/ar01-118.pdf. What they found out is that old circuit breakers work just fine. However, being mechanical devices, they benefit from occasional exercise and the recommendation is to pull and reset each one once a year to clean the contacts. (This might be a good addition to the annual inspection checklist).

As far as wearing  them out, the Klixon pull-type breakers are rated for 5,000 cycles with a resistive load and 10,000 mechanical cycles with no load.  Now a typical switch is rated at 25,000 to 50,000 cycles, so you can see that if you regularly use a circuit breaker as a switch it will wear out sooner than a switch. But a few pulls here and there are not going to impact the reliability of the breaker and can be beneficial.

sensata-7274 series-high performance circuit breaker-datasheet-1.pdf

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[47U]

5 hours ago, PT20J said:

I have pulled and reset some more than they probably have ever been exercised in their lifetime.

I would add that if you have a vintage Mooney like mine from the early ‘60s where the CBs are of the ‘reset only’ design, it would be a good idea to upgrade.  I was adding a terminal and when tightening it the housing (Bakelite?) shattered.  I replaced them all with the Klixons.  

If you still have these, you’re due for an upgrade.

   

[0TreeLemur]

When we put a JPI EDM900 in our C in 2018 under the watchful eye of our A&P IA, my co-pilot, being a small person, volunteered to do the airplane yoga associated with getting under the panel on her side of the aircraft and hooking up the power wire to a spare 5A CB.    She's not super strong.  She was using an electronics screwdriver.  While tightening one of the terminals, the plastic casing broke!  Being suspicious, I asked her to try torqing another one.  That one broke too!

They looked like the original Apollo-era CBs.  So we decided to replace all of them.  She methodically labeled and removed each wire, and removed each CB.  Almost all of them were brittle.  So while their electrical functionality might be robust, the plastic cases used in those '60's era CB's in our C had aged and become weak.

Same issue reported by @47U while I was typing this!

[John Mininger]

The question I would ask is: If you're going to the time and expense of replacing the entire panel, shouldn't one replace the old Klixon rocker switch breakers with Tyco toggle switch breakers?

[N201MKTurbo]

3 hours ago, John Mininger said:

The question I would ask is: If you're going to the time and expense of replacing the entire panel, shouldn't one replace the old Klixon rocker switch breakers with Tyco toggle switch breakers?

Don’t you mean Klixon toggle switch breakers? Like the ones used in the older Mooneys. If you mean Tyco, which breakers are you talking about?

[jaylw314]

27 minutes ago, N201MKTurbo said:

Don’t you mean Klixon toggle switch breakers? Like the ones used in the older Mooneys. If you mean Tyco, which breakers are you talking about?

I think he's talking about switching them with non-aviation parts, which I suppose you could do if your A&P and any future IA are willing to sign off on it, but that's a whole 'nother can of worms   it's not like the ETA switches used in newer Mooney's are any easier to find

Still, I can see the appeal.

Edited December 20, 2021 by jaylw314

[John Mininger]

For what it's worth, my avionics guy said that he would install these with a new panel: TYCO CIRCUIT BREAKER W31 SERIES | Aircraft Spruce

He said they are approved by various agencies that approve electronic components, UL, CSA, etc. And they were/are used as factory parts by Cessna, Piper and Beech.

Anyway, that's the answer I got when I asked the specific question.

[N201MKTurbo]

6 minutes ago, John Mininger said:

For what it's worth, my avionics guy said that he would install these with a new panel: TYCO CIRCUIT BREAKER W31 SERIES | Aircraft Spruce

He said they are approved by various agencies that approve electronic components, UL, CSA, etc. And they were/are used as factory parts by Cessna, Piper and Beech.

Anyway, that's the answer I got when I asked the specific question.

Oh, OK, those are the old Potter and Brumfield circuit breakers. Quite a bit cheaper than the Klixon and it looks like they can be packed closer together.

The FAA seems to turn a blind eye to panel work. It seems like in a perfect regulatory world you would need an STC for that kind of work, but let's not poke that bear.

[John Mininger]

3 minutes ago, N201MKTurbo said:

It seems like in a perfect regulatory world you would need an STC for that kind of work, but let's not poke that bear.

Ah, no. Let's not. :-)

[Marauder]

The big question is will they mount to the buss bar without any modification.


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[cliffy]

On the old red breakers one can power the system and ground a wire from the down stream side of the breaker to see if it pops and then reset it. 

If it works its good. leave it alone unless you really want the expense of all new breakers. Everyone has different desires. 

[N201MKTurbo]

It’s not like they are going to wear out. They have probably never actuated. Corrosion and dried up lubricants are the only failure mechanisms. Just think of that spring that has been cocked for 60 years just waiting to release its stored energy. 
 

The best way to test them is to get a constant current lab power supply and test them against their characteristic current/time curves. I would suspect they are still in spec. A little Tri-Flow down the side of the buttons wouldn’t hurt.

[DCarlton]

One thing leads to another...  while working under my right side panel, I noticed that the output tab on my 2 A circuit breaker is a millimeter away from the case on the manifold pressure / fuel pressure gage.  Looks like a short that's been waiting to happen for 30 years.  Hard to believe someone thought that was satisfactory.  Now I'm wondering how to resolve without replacing all the breakers; not looking for more work.  Doubt I can bend the tab; could stuff an insulator in there but might not stay in place dependably.  Most certainly the cases on these gages are conductive...   

 

Update:  Looks like the mid  60s Mooney's (or at least mine) had a cardboard flap between the breakers and the instrument cases above the breakers.  Cardboard has long since deteriorated.  Gotta get an insulator back in there.  

[Bob Weber]

The biggest killer of breakers is a loose connection in my experience.

I recommend checking all the screws for tight, anytime you find yourself in that area.

My all time winner so far, a breaker switch feeding an avionics master buss in a 340A.

The  "Australian Hall of Flame", a foot of the 10 gauge wire feeding it needed replaced as well.

His trim system worked better than he ever remembered after the repairs.

[PT20J]

Can you cut a piece of thin plastic and glue it to the gauge?

[DCarlton]

47 minutes ago, PT20J said:

Can you cut a piece of thin plastic and glue it to the gauge?

I managed to slide an adhesive backed piece of rubber between the top of the breaker row and the bottom of the gage.  It’s not moving.  I was hesitant to move the old manifold / fuel pressure lines around too much.  One day I’d like to get the old fuel and oil pressure lines out of the cabin [edm930]. 

[cliffy]

Don't take this the wrong way but if those lines are so old that you are cautious about handling them then maybe its time to replace them.

I've seen fuel pressure lines so old they just bust like spaghetti when removed. One had a date on it of 1963. It was well over 50  years old

for a rubber hose carrying pressurized fuel. Be cautious and check the dates Not something one might want to cheap out on. 

The other line that most forget about is the hyd line to the flaps under the cabin. Have seen several that were date of aircraft manufacture.

It can be challenging to change but it has to be done to keep our fleet going. 

[DCarlton]

1 hour ago, cliffy said:

Don't take this the wrong way but if those lines are so old that you are cautious about handling them then maybe its time to replace them.

I've seen fuel pressure lines so old they just bust like spaghetti when removed. One had a date on it of 1963. It was well over 50  years old

for a rubber hose carrying pressurized fuel. Be cautious and check the dates Not something one might want to cheap out on. 

The other line that most forget about is the hyd line to the flaps under the cabin. Have seen several that were date of aircraft manufacture.

It can be challenging to change but it has to be done to keep our fleet going. 

Replacing the lines would be a cost effective alternative to upgrading the gages to digital (or a good interim solution).  I suspect a lot of folks are flying with original lines under the instrument panel.  So hard to access and inspect.  I'll take a closer look.  

[47U]

3 hours ago, cliffy said:

The other line that most forget about is the hyd line to the flaps under the cabin. Have seen several that were date of aircraft manufacture.

Part of the problem here is that Mooney used Stratoflex 193 hose, which isn’t rated for fluid.  It rated for low pressure air/vacuum.  My friends G model had a puddle of 5606 on the floor of his hangar one day last summer when this hose failed at an adel clamp.  

I was surprised it was a 193 hose because when I installed new hoses in my ‘63C, this hose was Stratoflex 111, rated for hydraulic fluid.  Someone before me had upgraded the hose from 193 to 111.  I initially thought someone had installed the wrong hose in my friends G model, until I looked up the part number.  Surprise, surprise.  I had some -6 193 hose in work order residue so that’s was we replaced his failed hose with.  As for me, I’m sticking with my 111 hose.

[cliffy]

IIRC I looked up and read the actual spec sheet a long time ago for the MIL SPEC for the 193 hose qualification (H 5593-C) and in that it says

that 193 hose meets a certain spec (4.4.3.7 paragraph) for immersion in 5606.  Basically the MIL spec does require a certain amount

of resistance to petroleum products but its not specifically designed for it.  So 50 + years of immersion of course might cause a leak

even in a static pressure hose. 

 

 file:///C:/Users/72773/Downloads/MIL-H-5593C.pdf