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Thread: CKT Breakers

  1. #1
    Jim Heffelfinger's Avatar
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    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 Name:  pptc.jpg
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    It can be added to a terminal block via severing the connection between the mounting screws placing the fuse in series with the ckt. Name:  IMG_1180_small.jpg
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    Consider the zero panel space, and ease of hookup and no jumble of wires.

    http://www.littelfuse.com/products/resettable-ptcs.aspx
    Last edited by Jim Heffelfinger; 05-24-2018 at 04:50 PM.

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

  3. #3
    Jim Heffelfinger's Avatar
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    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

  4. #4
    CarlOrton's Avatar
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    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?

    Carl Orton
    Sonex #1170 / Zenith 750 Cruzer
    http://mykitlog.com/corton

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    Quote Originally Posted by Mike M View Post
    I didn't know automatic resets were legal. How about that! https://www.gpo.gov/fdsys/pkg/CFR-20...oup-id1320.pdf
    "Trip free" breaker definitely required on a certificated airplane.

  6. #6
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    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
    Last edited by cub builder; 05-26-2018 at 08:16 AM.

  7. #7

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    Quote Originally Posted by martymayes View Post
    "Trip free" breaker definitely required on a certificated airplane.
    Trip 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.

  8. #8

    Please note

    Quote Originally Posted by cub builder View Post
    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

    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.

  9. #9
    Jim Heffelfinger's Avatar
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    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

  10. #10

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    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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