CKT Breakers

Dick Koehler's hints on mounting circuit beakers brought up something I wanted to put out to this forum. Resettable ( automatic) fuses where no panel space is required and can be build right into the terminal strip. The "fuse" is a PPTC https://en.wikipedia.org/wiki/Resettable_fuse . It comes in a wide variety of values
and looks like this for our purposes : it does come in other configurations and commonly SMD. For circuit boards Attachment 7281
It can be added to a terminal block via severing the connection between the mounting screws placing the fuse in series with the ckt. Attachment 7280
Consider the zero panel space, and ease of hookup and no jumble of wires.

http://www.littelfuse.com/products/resettable-ptcs.aspx

I didn't know automatic resets were legal. How about that! https://www.gpo.gov/fdsys/pkg/CFR-20...oup-id1320.pdf

I am planning on one panel ckt bkr that covers the panel master switch with a PPTC on every device even if a switch has multiple devices connected. eg - Comm/Nav switch

Interesting; am ignorant on them, so haven't researched. What happens if it's a hard short; it just keeps a-poppin', or is there some point where it just blows?

Quote:

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Originally Posted by Mike M

I didn't know automatic resets were legal. How about that! https://www.gpo.gov/fdsys/pkg/CFR-20...oup-id1320.pdf

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"Trip free" breaker definitely required on a certificated airplane.

per AC43.13-1B Chapter 11 (Electrical) section 51, paragraph b.
Automatic reset circuit breakers, that
automatically reset themselves periodically, are
not recommended as circuit protection devices
for aircraft.

It doesn't say illegal, but it does say not recommended. However, if memory serves correctly, the two Stinson Voyagers I owned years ago were both equipped with automatically resetting circuit breakers.

Think about this situation. If a device smokes when power is applied, you may want the capability to completely and permanently remove power. I have run across that situation with a solid state wig-wag controller. The switch that turns on the wig-wag device gets it's power from the wigwag controller itself. When it failed, it had both smoke and sparks, that continued until power was completely removed. If power was re-applied it would start sparking and smoking again. Since the wigwag controller supplied the power to the switch, that meant the power had to be removed ahead of the switch via either circuit breaker or shutting off the master switch. You might say that's a less than ideal wigwag controller, but I know for a fact there are a lot of these very light weight wigwag controllers flying around in both certificated and Experimental Aircraft. There may also be other similar devices, and sometimes these types of failures can't necessarily be anticipated, which is why you may want the ability to pull a breaker or otherwise disable a circuit.

-Cub Builder

Quote:

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Originally Posted by martymayes

"Trip free" breaker definitely required on a certificated airplane.

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https://2.bp.blogspot.com/-bmsyokdhp...ngineering.gifTrip Free Circuit Breakers are circuit breakers which can trip even if they are held in the "ON" position. Hence, it is not possible to forcibly keep them in the closed position. Trip free circuit breakers are used in circuits with equipment which are sensitive to overload and in circuits which are not critical.

After looking up the definition of "trip free" it's obvious that "trip free" is the choice for aircraft even though I don't know the reference that requires it. The Littlefuse products the OP referenced are "trip free" because the operator can't forcibly keep them in the closed position. And I don't have the slightest idea what "trip free" has to do with "automatic reset" which was the OP's topic.

But wait, there's more! Since "the reg" says automatic reset circuit breakers may be used as integral protectors for electrical equipment if there is circuit protection to protect the cable to the equipment, does that mean one must have a circuit protector (fuse or cb) at the bus to serve the cable running to the auto reset cb which is mounted integrally with the equipment? That sounds silly.

The more regs, the more confused I get.

Quote:

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Originally Posted by cub builder

per AC43.13-1B Chapter 11 (Electrical) section 51, paragraph b.
Automatic reset circuit breakers, that
automatically reset themselves periodically, are
not recommended as circuit protection devices
for aircraft.

It doesn't say illegal, but it does say not recommended. However, if memory serves correctly, the two Stinson Voyagers I owned years ago were both equipped with automatically resetting circuit breakers.

Think about this situation. If a device smokes when power is applied, you may want the capability to completely and permanently remove power. I have run across that situation with a solid state wig-wag controller. The switch that turns on the wig-wag device gets it's power from the wigwag controller itself. When it failed, it had both smoke and sparks, that continued until power was completely removed. If power was re-applied it would start sparking and smoking again. Since the wigwag controller supplied the power to the switch, that meant the power had to be removed ahead of the switch via either circuit breaker or shutting off the master switch. You might say that's a less than ideal wigwag controller, but I know for a fact there are a lot of these very light weight wigwag controllers flying around in both certificated and Experimental Aircraft. There may also be other similar devices, and sometimes these types of failures can't necessarily be anticipated, which is why you may want the ability to pull a breaker or otherwise disable a circuit.

-Cub Builder

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14 CFR 23.1357 trip free breakers are mandatory for certified aircraft. I replaced automatic breakers in about a dozen Stinsons after I inspected one that almost was lost to electrical fire. Stinsons were certified under CAR 3, not FAR 23.

Lots of semantics and definition issues. The Stinsons were build before the PPTC technology existed.
If you have a ckt protected that has several sub-circuits each using the one fuse/breaker there can be issues. If your wig-wag has a switch in line with the fuse/breaker there is your safety for the buss.
As long as there is trip current in the ckt the resettable (PPTC) fuses will not return to conduction.
We are talking experimental. The AC43.13 has not been updated to 21st century technology as well as the CFRs
PPTC devices do not violate CFR 23.135

For an experimental, fuses are way underrated. I'd go with the auto blade type before I put in CB's.

Quote:

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Originally Posted by martymayes

For an experimental, fuses are way underrated. I'd go with the auto blade type before I put in CB's.

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I did.

But until I started reading this thread, I didn't even know there were such things as self resetting breakers.

I'm a former Stinson owner and replaced the re-setting CB's in my plane when I rebuilt the panel. Fast forward about 20 years and I installed spade fuses in my EAB. My current practice when flying certified airplanes is if a circuit breaker trips in flight I do not reset it until I'm back on the ground. My EAB is strictly a VFR aircraft so it was an easy decision to install fuses since I'm not going to replace any in flight. Compared to CB's fuses are lighter, smaller, more reliable and cheaper. What's not to like. There are lots of options out there, this is the one I chose but I'm not suggesting it's right for everyone.

As an engineer, I design with PPTCs regularly. If you use them in an aircraft, do read the data sheet carefully. In particular they have some characteristics you have to keep in mind. One is that they don't cut off the voltage and current to the load like a fuse or breaker, they simply go to a high-resistance state. A tripped PPTC can still deliver a few hundred milliamperes or more to a load. Secondly, they may not return to the same low-resistance state they were originally in for some time after the load is removed. There can be a residual higher resistance that may last for some time (minutes, hours or days). Also note that these are temperature-driven devices: they have a 'hold' current at which they are guaranteed not to trip and a 'trip' current where they are guaranteed to trip. The spread can be some number of amps, eg, 3A hold and 8A trip. The more amps flowing through the PPTC, the hotter it gets, and at some elevated temperature it trips. The hotter the device is to begin with (think parked on an Arizona ramp in the summertime) the lower the current will be when the PPTC trips. (Fuses also need to be derated for temperature, but typically not at levels seen in aircraft.)

Nothing wrong with PPTCs when used appropriately. They'd be fine, for example, to protect servo or trim motors from temporary overloads. I'm not sure they'd be as useful for protecting the wiring to, say, an intercom. An intercom is unlikely to trip a fuse or breaker unless it fails catastrophically, and in that instance I'd rather just have power cut altogether rather than have the PPTC cycling power on and off to a smoking intercom.

I was looking for an automotive resettable circuit breaker to protect my 12v battery and multiple devices. Luckily, I came across this Ampper model. The package includes two pieces, making it a great value option if I need to install breakers on different circuits.