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  • Circuit Breaker Switches

    Hey All...

    Thinking of going to all circuit breaker switches instead of switches and separate fuses or circuit breakers for my electrical. Any downsides to this? My mechanic friend loves them because it makes wiring much easier.

  • #2
    My understanding is that they have a higher failure rate than regular switches and, of course, are more expensive. I agree that they simplify wiring, but being a cheapskate I'm going to do the same thing on my Bearhawk that I did on my RV-8 and use switches with an automotive style fuseblock.

    YMMV, batteries not included, objects in mirror are closer than they appear, etc

    Mark
    -------------------
    Mark

    Maule M5-235C C-GJFK
    Bearhawk 4A #1078 (Scratch building - C-GPFG reserved)
    RV-8 C-GURV (Sold)

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    • #3
      We used circuit breaker switched on a rebuild years ago. They worked awesome with no troubles for 10years. I’ve been told they have a significantly higher failure rate but I didn’t experience any issues.

      On the BH we used a fuse box and switches.
      Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

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      • #4
        I used them on my RV6 and Legal Eagle, Plan on doing the same with my LSA. Had no problems with Breaker switches the past 14 years, so that's good enough for me.

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        • #5
          I've also been told they wear out. Maybe they do in something that is used every day. Tyco rates them for 10,000 mechanical cycles. I'm not going to touch that.
          From a tripping standpoint they're rated at more cycles than a standard breaker. 6000 vs 1000.

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          • #6
            I have use circuit breaker switches on two projects. No failures on either planes. It reduces the number of connections and failure points. You don’t need to figure out where to store spare fuses and you can reset the circuit quickly. A note of caution, I would only reset the circuit one time until I got back on the ground where you can safely troubleshoot the circuit.

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            • #7
              It could be that using a breaker switch would leave a longer length of unprotected wire, right? I put the fuse block a short run from the battery, and then all of its outgoing wires are fused. If you have more and longer wires going to the switches, and you don't secure them well enough, that could pose some risk worth considering.

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              • #8
                I recalled that I had one switch failure shortly after rebuilding the Luscombe, the plane I installed tyco breaker switches. It was within the first 100hrs. After than no issues.

                I went with fuses mostly because the breaker switches wouldn’t fit where I wanted to put the switches. I’ve been totally happy with the fuses.
                Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

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                • #9
                  Because I am lazy, if I was adding something on later, I might use a CB switch if it was not a critical item. Another downside to using them like this is the wire from the bus to the CB switch is unprotected.

                  More than half of all system failures I experienced over 30 years of flying for living were actually the failure of the switch, or CB. Usually the CB. For my new-build, I am using fuses.

                  I have been messing around with electronics since I was a kid. I have had quite a few switch failures in 12V circuits in a lot of applications. I can't recall ever swapping out an automotive relay. I am using a power module with fuses and automotive relays. I know the switch that controls the relay can also fail, but the only purpose of the switch is to turn a circuit off in the even of a failure, or to check the function of the backup. Normal operation, the switches don't move, and the relays are in the their un-energized, resting state. They are all dual pole relays.

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                  • svyolo
                    svyolo commented
                    Editing a comment
                    Thinking about this for a bit, I would say the least reliable switch type I ever saw was probably the big, heavy, battery selector switches used in Marine applications. Starter relays are probably #2. But I also heard the old school battery relays used on aircraft fail as well.

                    I also recall LEMO headphone jacks are far more reliable than the old school phono style plugs. I don't recall have an issue with a LEMO plug or socket. They were pretty common on the old style plug sockets.

                • #10
                  On the failure of relays, something I noticed on a couple certified birds is they wired the starter relay after the battery relay in series. The battery relay being rated for something like 60A continuous and the starter 600A for short duration. Naturally pulling a few hundred through the battery relay doesn't make it last that terribly long.

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                  • svyolo
                    svyolo commented
                    Editing a comment
                    You definitely need an appropriately sized battery relay, but there is at least one good reason to wire it that way. If the starter relay sticks closed, you can still shut it off with the master. Some cars (most?)aren't wired this way. I have had the starter solenoid stick "on" on 2 different older cars. I had to disconnect the battery ground. I had a girlfriend that had the same thing happen and she didn't know what to do. The car burned to the ground.

                    At least cars don't have a 7 foot club swinging around when that happens.

                  • zkelley2
                    zkelley2 commented
                    Editing a comment
                    For the starter relay you should be using a powered switch not a switch to ground. Then you don't have that issue.

                    They might make 300A continuous relays but I've yet to see one on an airplane.

                • #11
                  I went back and went through this section in The Aeroelectric Connection. I don't think I looked at that section before. He doesn't bad mouth anything, but expresses a preference for fuses. He also mentions switch CB's, doesn't say they are bad, but they do reduce wiring complexity by 1 wire and 2 terminals per circuit. His preference is for integrated switch/fuse/CB panels that reduce each circuit by 2 wires and 4 terminals per circuit. A disclaimer is that some of these products are simply wired with 2 wires and 4 terminals internally, which doesn't fix the complexity problem. There are some sealed, marine grade units in various sizes that are solid copper internally, which is what my panel has. A VPX reduces the wiring complexity as well. My solution weighs about the same but is cheaper. I still like the VPX.

                  Half the reason I went the route I did was it reduced wires and terminals. I have EFI and if my electrics don't work, neither does my engine.

                  I would still consider a switch CB if I was adding something later.

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                  • #12
                    I have installed the classic battery master relay, and starter relay. I think its pretty representative of what the industry has installed since about 1946. Mine weighs 13oz, and consumes .8 amps to keep the juice flowing to the buses, but is inexpensive from a reputable aircraft electrical supplier. Saying it another way, my relay consumes 12% of my continuous electrical demand.

                    So I'm curious about automotive relay.
                    Brooks Cone
                    Southeast Michigan
                    Patrol #303, Kit build

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                    • svyolo
                      svyolo commented
                      Editing a comment
                      I have a classic starter relay, but splurged on a Gigavac master relay. I splurged ($150) because primarily it consumed a lot less power, and was supposed to be more reliable. I am not sure it was necessary. I thought those classic relays used about 3-4 amps. The micro automotive relays use very little, I believe less than .1 amps, maybe much less than that. The way my panel is configured, they are all unpowered in normal flight configuration. They consume no electricity. If I need to turn the backup on, then the relay's coil is energized.

                      The way airplanes are wired it is pretty easy to hotwire over a failed master switch, relay, or starter relay. I might have wasted my 150 bucks on the Gigavac. But hey it looks cool. But then again, nobody sees it. I will use it.

                  • #13
                    Just another data point on circuit breaker switches. We have several on our Mooney. Fuel pump, nav lights, anti-collision lights, landing light, pitot heat to name a few. They are pricey. A few of ours have started to fail. What happens most often is they will not hold the contact closed or become weak. Rough air will knock them offline. Contact cleaner only goes so far. Did I mention they ONLY lasted 57 years! I’d like to see some actual data that showed they were any less reliable than a regular switch. It’s the moving parts that drive the reliability numbers/cycles.
                    Eli
                    Building BH 4 Place #503
                    Arab, AL

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                    • #14
                      Bob K on his forum had a write up that drove me to what I ended up doing, or what I am attempting to do as mine hasn't flown yet. He wrote a paragraph that the height of mankind's achievement in electrical reliability is the modern car. And he noted that most EAB's are wired like WW2 aircraft. I ended up tearing into auto electrics for a business I had, so I know how they did it at least until about 13 years ago. Minimal connectors. Minimal or no spade connectors, no ring connectors on anything smaller than 8 gauge or so. The few connectors were the highest quality they could do. Sealed, waterproof.

                      The VPX goes a long way toward this, but I don't have any experience with it. I really like their power panel product but still didn't buy it. I still might as I like it.

                      Circuilt breaker switches at least reduce the number of physical connections, as do fuse blocks. If I built the simplest of aircraft electrical systems I would have a hard time not using fuse blocks. Fewer terminals is always better. Less to fatigue, corrode, ultimately fail.

                      Between circuit breaker switches, or fuse blocks and switches, I would probably choose fuse blocks and switches. They both reduce electrical connections I think a similar amount. Which is more reliable would depend on the individual components used. Too many variables to comment on which is better but both reduce electrical terminals.
                      Last edited by svyolo; 10-30-2021, 01:15 AM.

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                      • #15
                        I have a VPX in my RV-8 and it's been a great and reliable unit. I opted for fuses in my Companion build because of the cost, but if cost wasn't an issue, I'd do the VPX again. In addition to the ECBs, the VPX has a number of nice features built in like starter circuit cut out, wig wag, trim servo control and because it interfaces with glass panels (like Dynon), you have a convenient way to turn on/off/reset your circuits. It's very nice, but this time, I didn't want to spend the money.

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