Is it to protect the wiring? or the instruments?
Keep the smoke in the wires
I always wondered how electricity works.
Thanks. I thought it was the wiring.
Well here is the main reason I asked the questiion:
I was thinking to put few RELAYs like (S704-1 form B&C) in the wingtip to control switching of nav, landing, strobe and even pitot. Then I would only run one power line into the wing with several thin wires to control switches.
1) Does this make any sense?
2) If the fuses are to protect the wiring, then I only need one fuse to protect the main wire that goes out to wing to supply those components. Right?
Ben
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Lets say you want a landing light, nav light, strobe unit and Pitot heat on one circuit. You could run one large wire (probably 12 gauge) to the wing tip, along with 4 control lines. In the wing tip you'd have 4 relays, along with 4 fuses or circuit breakers for the individual circuits. This would prevent any one circuit fault from taking out the others. You'll need access to the fuses. A good location would be under the wing tip lense for easy access and visibility. Now THAT will stop you from diagnosing a fault in flight!
Is this simpler and more reliable than the traditional method? Not sure.
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I think a properly designed distributed system could save several pounds of weight and provide excellent fault diagnosis.
Vern
Along that line. switch-style breakers also work well in aircraft applications. Saves weight (wiring and components), saves $$ (wiring labor and components) and reduces the chance of part failure (fewer connections). Downside is that it's harder to tell if it's tripped.This might sound funny from a guy who works in the space program, but I agree with keeping things as simple as possible (and no simpler). Switches are pretty darn robust, and relays are finicky....why have two devices to do the task when one has been used in virtually every airplane around. If the idea is to experiment, then that's OK...if the idea is to have a reliable, robust system - I'd buy good switches and few relays.
Paul
Thanks. I thought it was the wiring.
Well here is the main reason I asked the questiion:
I was thinking to put few RELAYs like (S704-1 form B&C) in the wingtip to control switching of nav, landing, strobe and even pitot. Then I would only run one power line into the wing with several thin wires to control switches.
1) Does this make any sense?
2) If the fuses are to protect the wiring, then I only need one fuse to protect the main wire that goes out to wing to supply those components. Right?
Ben
I agree, in general that the benefits are slim. KISS works, and failures are isolated.
Back in the 1980's IEEE Spectrum publish a graph on the probability of success for any particular solution to a problem. In summary it said this: Simple, limited function, high probability. Complex, comprehensive function, high probability. Everything else in the middle, lower probability.
It's a classic bathtub curve (Like a 'U').
This curve applies to everything from pens to space shuttles. I've seen many products fail because they fell somewhere in the middle. Switches, Breakers and wires = simple. Vertical Systems products = complex. Will Vertical Systems succeed? Yes, if the complexity is so great that it handles all reasonable failure modes, provides clear benefits and is reasonably priced. The big challenge is price. I can provide a protected circuit on my airplane for $7.50: $5.00 for the switch and $2.83 for the circuit breaker.
What! $2.83 for a circuit breaker? Go to Digikey and search for W28 series breakers. I use 22 of them in my airplane, and they work fine. They are cheaper than a fuse holder + a fuse.
V
It is!!!Thanks. I thought it was the wiring.
It is!!!
Quote:
Originally Posted by N787R View Post
Thanks. I thought it was the wiring.
Not exactly, the "bible" (AC 34.13) says this -
11-47. GENERAL. All electrical wires
must be provided with some means of circuit
protection. Electrical wire should be protected
with circuit breakers or fuses located as close
as possible to the electrical power source bus.
Garmin can do what ever they want...As an example, the GTX-320 manual calls for 20 g wire and a 3 Amp fuse.
In this case, the fuse is sized to protect the device first, not the wire.
Garmin can do what ever they want...
Fuses are to protect the wire
If it happens to protect a device ... that is a nice side effect.
The question was " What is the purpose of fuses and breakers ?"
The question was not what does the fues do...
The purpose of the fuse is to protect the wire!
In you house you there is a 12ga wire with a 20 amp fuse...
It doesn't know or care what is plugged in...
The 20 amp fuse is to protect the 12 ga wire
Bad comparison to aircraft.
Quote:
....
As an example, the GTX-320 manual calls for 20 g wire and a 3 Amp fuse.
In this case, the fuse is sized to protect the device first, not the wire.
This is a poor practice by the manufacturer. If the unit requires a fuse to protect the interior of the box, this fuse should be provided as part of the electrical design of the unit. The avionics devices that I design either have some form of current limiting or fusing bulit in to protect against internal component failure and potential fire.
To demand an external fuse to protect the device is poor practice. Oddly, I've seen it most with older Garmin products, before they purchased UPSAT, which brought more aviation 'best practices' to Garmin.
This might sound funny from a guy who works in the space program, but I agree with keeping things as simple as possible (and no simpler). Switches are pretty darn robust, and relays are finicky....why have two devices to do the task when one has been used in virtually every airplane around. If the idea is to experiment, then that's OK...if the idea is to have a reliable, robust system - I'd buy good switches and few relays.