Popping a push to reset CB ?

[Genghis the Engineer]

Can anybody help me with this?

I'm proud joint owner of a Bo209, which was built in Germany in 1972. Joy to fly, well maintained, etc. etc.

One snag with it is that we have basically only a tenuous idea of what the bank of circuit breakers on the right hand side of the cockpit do. Yes, they're supposed to all be as per the wiring diagram, there is even a diagram inside the glove box that claims to state what all the CBs do. It is, frankly, a work of fiction. For blindingly obvious reasons, this doesn't make any of us very happy so sometime this winter I'd like to spend some time tracing what everything does and labelling it properly. That's well within my abilities.

Now the thing I don't know how to do - how can I pop the push-to-reset circuit breakers it's fitted with so I can verify which is doing what? This would clearly be far easier than much mucking about with long leads, circuit testers, removing bits of aeroplane, etc.

Not my picture or aircraft, but this image found online - you can see the CBs and just about the signage inside the glove box on the right hand side.

https://cdn.airplane-pictures.net/images/uploaded-images/2017/10/13/975136.jpg

Can anybody advise?

G

[EXDAC]

I enlarged the image and the circuit breakers appear to have exposed stems. If they do then why can't you pull them? My PA-28 has CB that are flush and they cannot be pulled. I have not seen an exposed stem circuit breaker that cannot be pulled to open.

Close up of breaker or read the part number off one of them?

[Genghis the Engineer]

Good question. I may be taking it on trust that they can't be pulled, but I'll double check next I'm down at the airfield.

G

[jimjim1]

I am NOT saying yours are safe to pull. However, here is one that is.

https://www.wicksaircraft.com/shop/push-pull-circuit-breaker/

Push/Pull Circuit breakers are single pole, thermal devices. Unit may also be used as a switch.

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/929x420/breaker_push_pull_45de39812bd747c8cdb3ada7a2a503b5da84b402.j pg

[EXDAC]

Some Klixon breakers can be pulled to open but Klixon suggests they should not be used as a switch so as to limit the number of push/pull cycles. My experimental has Klixon breakers and I have no hesitation to pull them if needed for a test. Switches are used for everything that cycles at least once per flight.

If in doubt look up the part number but the ones in the photo look more like the Potter Brumfield than the Klixon.

it takes a firm pull to open a Klixon but not familiar with the Potter Brumfield.

[dixi188]

There used to be a maintenance requirement to excercise CBs every few years and test the trip current at less frequent intervals.
I did this in the mid 1970s. We used a 20 or 25 amp power supply, a variable resistor and an ammeter. One lead was connected to the aircraft busbar and the other to the output side of the CB with the system wire disconnected. We had a few failures that didn't trip at the required current. I seem to recall something like- Rated current +20% within 20 seconds. This was on BN Islanders and maybe aircraft on the LAMS program.
I have Klixon CBs on my narrow boat and model railway.
Dixi.

[wrench1]

how can I pop the push-to-reset circuit breakers it's fitted with so I can verify which is doing what?
If they are not the pullable type CB, some of the older push type could be unlatched by pushing the button in while set/unpowered and it would open the CB. However, it is not common to see them in this day and age. While I'm not familiar with the ones you have installed based on your pic, most newer push-to-reset CBs cannot be manually tripped/opened by design unfortunately. And just to add if you are going down this rabbit hole to trace the circuits may also want to check the resistance across each CB and check for any high readings per the specs especially if they are original to the aircraft. Those type CBs have a tendency to internally corrode over time and may no longer meet spec. In most cases, I usually recommend to make the investment in replacing those CBs with pullable types when possible but it is a minor alteration for this side and may not be as easy on your side. Good luck.

[NutLoose]

Might be of interest to you Genghis and EXDAC, the later switches in the Cessna's have a combined switch / Circuit Breaker, see the bottom row of switches in this image, the value of the CB is on the end of the switch, so if the CB in it trips, the switch trips off. So it acts as a normal switch but as a CB when there is a fault.

I do not know the truth in this as not tried it.

There are some flush breakers that pop after you push and hold them for a moment.

https://www.pilotsofamerica.com/community/threads/question-re-autopilot-circuit-breaker.87998/


https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/800x518/auto_pilot_circuit_breaker_983a5e6bfe5681f76d6985385c9762f64 a2f4722.jpg

[EXDAC]

I have combined switch/breakers on several circuits in my experimental but they look like conventional toggle swiches. They have the advantage of taking less panel space than separate switch and breaker. I find the "feel" less pleasant than a good quality toggle switch though.

https://www.mouser.com/datasheet/2/418/4/NG_DS_1308242_W23W31_1208-719199.pdf

[Genghis the Engineer]

Well, with the assistance of another syndicate member, and the advice here, I tackled this.

Turns out that the accepted wisdom within the syndicate, and I think the wider Bolkow owning community, that these CBs could not be pulled was untrue. With a bit of careful application of force (and in a few cases a pair of pliers) I demonstrated that the CBs could indeed be pulled, then pushed back in to reset them. And, I now have an accurate and useable circuit breaker diagram for the aircraft that'll shortly get pasted inside the glovebox and as soon as the right tape arrives for my dyno printer, they'll be placarded as well. This makes me suitably happy.

Many thanks - help accepted, used, and gratefully appreciated.

G

https://scontent.flhr10-2.fna.fbcdn.net/v/t39.30808-6/384288837_7035322909820019_2286247170663061294_n.jpg?_nc_cat =111&ccb=1-7&_nc_sid=5f2048&_nc_ohc=-tLq_pUuiS4AX-IO58o&_nc_ht=scontent.flhr10-2.fna&oh=00_AfC9BhHiMv9-OKGwnkYiJNbP8Y-AsugVXki0CS-o0Mv0aQ&oe=6530B6A3

[NutLoose]

I was going to mention pliers, as have done it in the past, though it isn't exactly a good procedure. You know you can buy these.

https://www.aircraftspruce.com/catalog/cspages/09-35000.php

https://www.aircraftspruce.com/catalog/cspages/panelmarkset.php

[Genghis the Engineer]

I sort of did, but forgot - but the dyno tape's on order now anyhow, and this way I can exactly the wording I want. Cheers Nut.

Didn't need a lot of pulling with the pliers TBH, just something that could get a reasonable purchase, my fingers on the smooth CB stem not always being quite up to it. Amazing what's possible when, well, you know it's possible.

G

[Stuart Sutcliffe]

Genghis, if you are referring to the variously-coloured, self-adhesive tape used for embossed labelling, it is Dymo tape (not 'dyno'). The name derives from the company which popularised the product in the late 1950s. 😉

[Genghis the Engineer]

And, embarrassingly, is still the brand name of my tape printer! I sit corrected. :8

G

[dixi188]

I'd just claim "Fat Fingers", the M&N are next to each other.