switches and circuit breakers

hi all,
im not too savvy in this area so I am looking for suggestions. my build is an SS, O-200, steam gauges, comm, transponder, lights. im looking at which switches and c/b's to buy. I was looking exclusively at aircraft spruce, but after searching threads on this forum I saw a mention for steinair. I went to their website and it appears much easier to shop. any other good websites or is this the best? it looks like the klixon 7277 c/b's would be best. as far as switches, some give specs for the volts and amps and the less expensive ones don't. i'm just a little confused.
thanks, ken

A lot of builders and light sport manufacturers are using ATC/ATO automotive style fuses in a fuse block over the Klixon type breakers now. This gives a greater selection of switch types, styles and sizes to choose from. It also can make it easier to wire your electrical system.

Selecting switches is based on the circuit's voltage and current ratings and whether it's AC or DC. Most small aircraft circuits are DC (ignition grounding circuits being the exception). Many switches have decent AC current ratings but much smaller DC ratings.

It's good to make a listing of your circuits and their respective maximum current draw. You'll use this to determine fuse or breakers ratings, wire sizes and select switches.

I think SteinAir is a good choice of vendor. They know what they sell and can answer questions about your type of installation. They also offer tools that are sometimes needed for crimp pins and connectors you typically find in aircraft.

Ken,
I am at the same point in my build. Attached is a spreadsheet document (in pdf format) that I used to list my circuit, breaker, and switch needs. I am planning on using the round rocker switches that Kitfox sells. I thought that they look nice and don't take up too much room on the panel.

I opted to use the EXP Bus system because of the simplification of the install and the safety of the solid state protection and soft start capability for the electronics.

It is just another option you can consider.

http://www.affordablepanels.com/cata...tricalhubs.pdf

Aircraft Spruce handles the product as well.

http://www.aircraftspruce.com/catalo...ges/expbus.php

I know there has been a significant movement toward the fuses vs. circuit breakers. For me personally, I prefer the circuit breakers for the following reason. I will on occasion want to power up with certain circuits or devices off. This is very helpful since many modern electronic devices come with no on/off switch. With circuit breakers, it is as simple as pulling a pin or pins with no chance of mixing things up when going back to fully powered mode. This idea is similar to those who elect to have valves just down stream of each wing tank in the fuel system - which I don't. I have worked on both and don't really see an advantage to either in the wiring phase except having to make my own positive buss. I didn't particularly like the aesthetics of the fuse box which protruded outward from the panel about an inch with its cover and consumed about a 30 inch square piece of panel space. Like Ken, I was using steam gauges and needed the space for a chart box. I used the Klixon 7274 on my most recent project. Installing was simple as drilling spaced holes for each, then drilling similarly spaced holes in a strip of brass that then was screwed to the hot terminals of the breakers as a positive buss.

Regarding the switches and their current carrying capacities, with the LED lighting - position and anti collision, current capacity requirements have been greatly reduced and i honestly didn't pay too much attention to that.

Thank you. You've all been very helpful. ken

Also new to this and just starting to stick my toe in. If I don't go the VP-X way, can I have all my switches at 20amps lets say as long as my CBs/fuses all all correctly sized?

If there any reason not to use 20amp automotive rocker switches?

No reason at all, Josh. If you have a chance, try to read Bob Nuckolls' section on switches & circuit breakers in his AeroElectric Connection book.

What john said...
As far as fuses vs circuit breakers are concerned, breakers are re-settable in flight. Fuses, not so much. That is why civil and military aircraft typically use CBs over fuses.
There are bus bars made for circuit breakers that make it easy to separate the different busses you might need, i.e. essential, main, and avionics.
Yes these are experimental aircraft and I am a fervent supporter of those ideas. However some aircraft based best practices are there for a reason.
As for switches, there are AC and DC rated switches. At low current (assuming 12VDC) there is no much to worry about. At higher currents you will be dealing with average voltage and arcing. Will any AC rated switch work? yes. How long? Who knows. It wasn't designed or tested for that.
I opted for NTE 12VDC 20A rated rocker switches. Are they "aircraft grade"? nope. but they are 12V DC rated switches designed and tested to handle 12VDC at 20A. Anything 20A or less should be fine.
Steinair has a great site. The site has pics of pretty much everything so you know what you are getting. I highly recommend steinair.com if you are unsure of what you need or just need to see what you are asking for.
For placards I recommend engravers.net. Very nice custom placarding and very reasonable in cost.

I just spent my entire trip over from CA to Washington DC reading that very chapter of AeroElectric .."switches, relays and contactors". It was very informative. He covers everything including the "knife blade" switch they depict in Frankenstein. I learned a good deal reading this chapter.
Eddie

I do have the AeroElectric but I am finding it hard to sit down and read it cover to cover with all the studies I have going on right now. Maybe I will jump ahead to that chapter for now. Thanks for your input. Does he have opinions about fuses vs. CBs?

He most certainly does.
Eddie

Bob is a proponent of fuses and not resetting/replacing anything in-flight. Following that advise, I have mounted my fuse blocks on the back-side of my panel (with mostly fuses that illuminate when blown). We'll have to see how that works out in practice.

I did the same, essential circuits on the nearside of the panel and nonessential on the farside.

http://www.campbells.org/Airplanes/a...rsVsFuses.html

An interesting test comparison of fuses vs CBs

Quote:

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Originally Posted by jmodguy

http://www.campbells.org/Airplanes/a...rsVsFuses.html

An interesting test comparison of fuses vs CBs

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That was interesting, Jeff, but it's a pretty old article (2003) and the author specifically tested 3AG type glass fuses, rather than the more modern ATC type that are obviously much more robust. The result is that some of the negative conclusions he made about fuses don't pertain or are not relevant.

Then there is the cost factor, CBs are nearly an order of magnitude more expensive and take up more room on the panel. Not that I am biased, mind you.

My decision to go with CB's was very simply this: I wanted something that did not require having to have spare pieces stored where they could be quickly found. I already have to carry spare batteries for the headset, emergency handheld radio and flashlight, chargers for the phone, you get the idea. Too much stuff to keep track of.

I had a discussion today with a couple peers about this. We are in the wiring and interconnect business and between the 3 of us there was about 87 years of experience and best practice discussed for close to 30 minutes. Education levels included EET, EE, and Masters in Physics. We discussed test methods for both fuses and circuit breakers, systems installation best practices and what ifs. We also discussed things like standard CB in flight reset procedures, i.e. only once, and fuse practicality with the risk of FOD etc. We could not come up with a reason to use fuses over CBs for any reason other than cost.
Granted fuses are cheap and CBs are pricey at @ $20 each. If fuses are a better way then why do aircraft manufacturers from Cessna to Boeing use CBs instead of fuses?

My guess would be that Boeing and others will just pass the cost of those pricey objects on to us anyway.:D

Thanks Jeff. That is the way I have always felt. Regarding Bob Nuckolls. He was on one of the early Kitfox lists. He was one of the guys as we all are. It was not difficult to disagree with some of what he posted and agree with the rest. When he became the Guru those feelings persisted especially about Circuit Breakers vs. Fuses. Both N96KL and N338S have CBs. I have twelve on 338S - two labeled "Aux" expecting new add ons. The $$ were not a factor in the decision. In the 900 hours I put on 96KL - no breakers popped. No regrets.

I put C Bs on my Fox and was happy to see the 15 amp one popped one day on the electric IVO prop. Happy because it protects the motor on the prop from taking too much load and happy to know the breakers work. My Switches have LEDs in the ends and it was easy to spot that the breaker had popped because the LED was off.
I like the system.

Always a hot topic, but I look at it this way as an analogy:

If fuses were such a great and safe way of doing wire protection - every house in the country would still be using them instead of circuit breakers!

Kinda makes one think about it a little differently!

Greg

Quote:

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Originally Posted by Danzer1

Always a hot topic, but I look at it this way as an analogy:

If fuses were such a great and safe way of doing wire protection - every house in the country would still be using them instead of circuit breakers!

Kinda makes one think about it a little differently!

Greg

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A closer analogy relating to the equipment being protected might be: If circuit breakers were such a great and safe way of doing wire protection, every automobile in the country would be using them instead of fuses. ;)

Obviously, they can both be good and safe ways of doing wire protection. I believe that one of the main reasons for the abandonment of fuses in house wiring was that they could be too easily substituted with improper sizes (or even a coin or slug). Also the load on a particular circuit could be indiscriminately varied all over the map by anyone in a home, so it was probably eventually deemed imprudent to allow people to easily vary the amount of protection on a particular circuit. This could lead to all kinds of other discussions about government feeling the need to protect people from themselves.

I like circuit breakers... got 'em in my first homebuilt. I also like fuses... got 'em in my Kitfox.

My 912is folks think fuses are good. I have a whole box of em.

Just to throw a curve in the mix, I used "breaker switches" in my plane. They serve the purpose of both items and only half he space is taken in the panel.

Link. Yes they are expensive, but they work very well.

I have used breaker switches on previous projects, great way to simplify things and save panel space.

[QUOTE=Av8r3400;65226]Just to throw a curve in the mix, I used "breaker switches" in my plane. They serve the purpose of both items and only half he space is taken in the panel.

I think this just might be the clue. The typical CB pops when over amped and pushed to reset. Fuses would be a definite advantage over these as it allows for testing various circuits independently. The CBs I chose pop, but the button can also be pulled to open the circuit - switch off power. This function I have found to be a real time saver when trouble shooting or adding things and want to check them out without those auto on items running in the background.

I am building a 7SS/912iS using fuses.

I have a Glastar and reworked the panel to install a two screen Garmin G3X
8 years ago used all breakers

I am going fuses with the Kitfox as I have not had a breaker pop yet

David Kelm

I decided to check the Fuses in the Model 4 that I recently purchased and found that some of the AGC glass fuses were 32 volt DC and some where 250 volt AC.
Did some research but still don't really understand the difference.Checked out several automotive places that sell fuses and they list both types for sale under automotive.Could someone Please explain to me in as simple of terms as possible about these 2 types of fuses.
Can I replace a 10 amp fuse in the Fox with either a 10 amp 32 Volt DC or a 10 amp 250 volt AC fuse,will they both provide the same 10 amp protection in the Kitfox?
THANKS

Fundamentally, the AC fuse isn’t as good of a choice as the DC fuse in this application. In reality, it probably won’t make a difference at these voltages.

I’m not a fan of glass fuses in aircraft a) because they can break and b) because the holder clips usually are pretty exposed and can lead to inadvertant shorts. Maybe an upgrade to blade type fuses is in your future?

It doesn't matter which one you use. Both are rated for the same amps.

There are fast blow and slow blow fuses and you can decide which type you want dependent on the circuit it is powering. The slow blow ones can tolerate a short burst of current with out blowing. You can Google this if you want more info.

AC and DC fuses are built different. This is due to arcing when the element opens. AC circuit average voltage is zero. This is due to the symmetrical value of the voltage above and below a zero reference. DC circuit average voltage is the voltage in the circuit.
When you open a fuse in an AC circuit the voltage passes through zero volts very quickly and there is very little arcing. When you open a fuse in a DC circuit the voltage (and current) is still there, until the element has separated.
This is why production and military aircraft use circuit breakers instead of fuses.
Remember this, the circuit breaker or fuse is not there to protect your hardware, it is there to protect the wiring and prevent an inflight fire...