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Asking for advice on : circuit breaker. ⁉️

romanov

Well Known Member
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Hello Guys,

We see all the time black circles
type of fuses that jumps out
once done. Why we don't see
more LED warning fuses?
As we see in automotive.
Is it any aircraft related uniqueness ⁉️

Thanks a lot
Roman
 
We see all the time black circles
type of fuses that jumps out
once done. Why we don't see
more LED warning fuses?
As we see in automotive.
Is it any aircraft related uniqueness ⁉️

Thanks a lot
Roman

Roman- Fuses are fine but present three problems- They need to be physically replaced, are difficult to remove in flight, and taking advantage of the indicator types requires placement where they are clearly visible to the pilot. Most RV’s end up with at least a few fuses for non-essential loads, but pullable breakers are far better for important loads, allowing in-flight re-setting and offering a means to isolate the entire circuit right at the main bus. My 7A has 33 pullable breakers and 10 Fuses. Actually, two of the breakers are switchable 35Amp Klixon’s that supply power to the essential loads busses on my twin batteries, but these retail at $200ea. My fuses are under the panel and can only be inspected and replaced on the ground.- Otis
 
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I am using the LED indicator blade fuses in my RV-9A build using this Bussmann panel mounted rear terminal fuse block with cover. https://www.waytekwire.com/item/46074/EATON-s-Bussmann-Series-15712-14-06-21A-ATC-Fuse/
I figure the LED indicators will make it pretty easy to check their function during my pre-flight check and also in flight should there be a component failure. I used blade fuses in my RV-10 build but the fuse block was mounted on the sub panel behind one of my G3X screens. I like the idea of having it mounted on the front of the panel where access will be more ideal.
 
i don't think a popped breaker or a lit fuse would cause me to start trouble shooting in the air unless i can't control flight of the airplane. the circuit was opened for a reason....too much load on the wire.
lit fuses would be handy in preflight if you can see them. i could appreciate that. they are behind the glovebox door where the glovebox should be on my 12.
 
If you follow the Aeroelectric Connection philosophy (I largely do), then with only a couple of exceptions, there's no reason to access any circuit protection while in flight. Any electrical item important enough for safe conclusion of a flight should be backed up with something else capable of taking over its function. The only exception that comes to mind at the moment is the alternator field circuit breaker(s), and the only reason for that, is the remote chance of a no-risk voltage spike causing a false trip of the overvoltage protection circuit, which in turn, trips the field CB. Because of that 'false trip' possibility, the philosophy allows one reset attempt, on this one circuit.

To the original question, if you like lighted fuses, and don't mind paying extra for them, go for it. :)

Charlie
 
Fuses?

I think if I were doing it all over again I would use a small automotive fuse panel out of site but easy access. The only reason you need fuses accessible to you is if it is flight critical, Landing gear, Trim motors, fuel pumps. Let's be realistic, if the fuse pops it is because there is something wrong! The only reason you would want access to fuses is if you need to get the gear down with multiple attempts or shut off hydraulic or electrical motors that do not have on/off switches (Trim, servo, flaps, etc....) Things that would burn up if power is not taken away.

We are in an age of voltage protection and smart systems. As a former automotive electrical engineer, I like the idea of a small out of the way fuse panel with 30 cent fuses.
 
I also kept mine pretty simple. I have my PFD, MFD, AHRS, EMS, Auto pilot servos, and Alternator field on C.B.?s which are on the panel and easily accessible, but everything else is protected via fuses that are mounted on the sub-panel behind the MFD G3XT. I?ll have to pull the MFD to get to the fuse panel if I need to replace a fuse, but they are very easily accessible once that one screen is pulled out.

Mark
 
If a CB pops, it is because the plane is trying to set its self on fire, why would you try and relight this fire by resetting a CB? All blade fuses in my build on a full electric engine with back up everything and an on off switch for everything. Ill diagnose the problem on the ground.
 
If a CB pops, it is because the plane is trying to set its self on fire, why would you try and relight this fire by resetting a CB? All blade fuses in my build on a full electric engine with back up everything and an on off switch for everything. Ill diagnose the problem on the ground.

Bret - Good point, but I think the accepted strategy of trying one re-set has merit because occasionally a CB can get ?twitchy? and trigger on a small load. If the re-set is successful, the suspect breaker should be tested thoroughly or simply replaced and destroyed straight away.

As for never needing access to circuit protection devices in flight(from a different post in this thread), I?d argue that being able to selectively pull and re-set breakers in flight is a valuable diagnostic feature, especially if you get wiffs of ozone smoke or some subsystem starts acting up. All breakers on my bird are either pullable or switchable. Many use inexpensive resettable-only for high-load jobs like the B-lead, but I install the excellent pull-able versions offered by B&C Specialties even though they cost and weigh a bit more.- Otis
 
Fuses are never twitchy.

Fuse panels can be installed so they are accessible...and the supposed difficult of replacing a fuse in flight matches nicely with the old "wind your watch" advice. Think about it for a bit and you may decide the reset will wait until over the home drome.
 
We're each going to do what we're going to do. But I've found it instructive that there have been airliners lost while (read that: *because*) a 3 person highly trained crew tried to troubleshoot a non-critical electrical problem in flight.
 
This topic quickly digresses into a religious discussion. We each have our opinions as to how best to achieve circuit protection. To each his own.

I'll try to add a little value here by suggesting that, while I'm very strongly a supporter of "pullable circuit breakers" such as the Klixon 7277 or similar, I have used fuses in other applications. In fact I used LED indicating fuses in one application. I find the concept of troubleshooting fuses to be a challenge. Not because I don't understand how they work but because either a continuity tester is required or a significant amount of light is required to determine whether a fuse truly is "blown". For these reasons I would not choose to install fuses in an aircraft unless they were of the LED indicating style. One wants to be able to troubleshoot quickly and easily in austere conditions (including waaaay down at the end of the unlit visitor aircraft parking area). The LED indicating fuses support this methodology.

There's one aspect of this discussion that gets very little air play. Often times we will see electrical devices produce higher-than-normal loads in a one-off fashion. One of these that comes to mind is the flap motor on a cold morning where there might have been a drip of moisture that froze on a flap track. The flap motor suddenly encounters a brief load spike, thus producing a brief current spike. Some circuit protection devices are not sized with adequate "overhead" to allow a load to function under such slight over-load conditions. If a fuse was protecting the flap motor in this example, the fuse would blow and one would be stuck scrambling for a replacement. This is an example where a resetable circuit breaker has an advantage. Reset it once - if it pops again, you have more serious troubleshooting to perform. The nugget in this paragraph is that one never wants to have their circuit protection device sized to just barely cover the operating load of whatever is hanging off the far end of the wire. Size the wire for the max current of the load, then size the circuit protection device to protect the wire. I'm guilty of not having strictly followed this recommendation and I rue the day that I deviated from it because the results have always been frustrating.

Now for a question to those who have extensive experience with fuse-equipped aircraft. Where do you keep your spare fuses, and how do you keep them organized? I ask because I was sure I had kept a link to a compact fuse holder for the standard automotive fuses - it looked like a compact fuse block. For the life of me I can't find that reference, hence my ask about how you keep your spare fuses organized and easy to access.
 
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Now for a question to those who have extensive experience with fuse-equipped aircraft. Where do you keep your spare fuses, and how do you keep them organized? I ask because I was sure I had kept a link to a compact fuse holder for the standard automotive fuses - it looked like a compact fuse block. For the life of me I can't find that reference, hence my ask about how you keep your spare fuses organized and easy to access.

In the RV-10 I kept an assortment of blade fuses in a small snack size zip-lock and that was left in the map box. I'll do the same for the -9A. I numbered all the blade fuse slots and made up a legend that I laminated and kept in the map box also: slot number, item protected, and fuse amperage.
 
1. If there are extra slots in your fuse box, which is likely, store extra fuses there. You probably will never need one, certainly not many.

2. ?No reset of c/b > 5 amps in flight?. This is the limitation on the Part 25 Jet I fly. As someone pointed out, aircraft have been lost while flight crew attempted to diagnose problems. Do that on the ground. The one reset idea is out of date and, literally, playing with Fire.

3. Fuses are a good idea and very cost effective compared to c/b?s. A few c/b?s are needed where an item might need to be DE-powered in flight.

Roman, your plane doesn?t have to look like an airliner from the 60?s with c/b?s covering every more or less flat surface in the cockpit. Design it howbit makes sense to you.
 
Beware. I used to use LED lit fuses as they seemed like a good idea. A couple of years ago I delivered a newly-built experimental Backcountry Super Cub to the owner flying from FL to New Mexico. The aicraft had an automotive fuse panel on the kick panel filled with blade fuses that lit up on failure. The onboard USB charge port seemed to work fine for.about two hours and then stopped charging. When a portable device was plugged into the port it would recognize the power and show it was charging. But it would not charge and would actually discharge. Ultimately the culprit was a failed fuse. The small current used to feed the failure light was enough to keep the USB port lit up and cell phones and iPads tricked into thinking they were charging but not enough to have it act properly. Now when something still powers up, there doesn't seem an immediate need to check the fuse. After hours of trouble shooting replacing the fuse was the answer. Adding to the frustration the failure light was too dim to make out in daylight and a crude continuity check showed things good.

Once I stopped to think about it I realized that upon failure there has to be enough current to light up the failure light. Not a problem for most legacy circuits but definitely a problem for modern low-power digital devices. And the continuity checker could pass the LED (probably in only one polarity so I guess I hit the 50/50 chance).

I switched thenwhole.bus to non-indicator blade fuses and the failure gremlins went away.

So fuses are great. But beware the "illuminating upon failure" type. ��

Jim
 
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resettable c/b for a blade fuse holder

As a kind of half & half solution, I bought some resettable c/b's that will fit in a blade fuse holder, though mostly so I could safely bench test electrical systems as I build. Possibly I may fit these in the finished plane (in several years time), but mainly for low power and non-critical things. These have a distinct pop-up tell-tale when they trip, and won't reset while o/l current is still there. The only downside is they are 15mm or so taller than a fuse so they need a little more space, but still relatively cheap compared to a "proper" c/b.
 
Good thread. Thanks Jim for that information, never considered how the led comes on when the fuse burns out, but now I can see the problem. Sounds like a good electrical diagram with clearly labeled fuses is the way to go for troubleshooting.
 
As a kind of half & half solution, I bought some resettable c/b's that will fit in a blade fuse holder, though mostly so I could safely bench test electrical systems as I build. Possibly I may fit these in the finished plane (in several years time), but mainly for low power and non-critical things. These have a distinct pop-up tell-tale when they trip, and won't reset while o/l current is still there. The only downside is they are 15mm or so taller than a fuse so they need a little more space, but still relatively cheap compared to a "proper" c/b.

Where did you source these wee beasties? They sound like an interesting compromise perhaps...
 


👍👍👍


Thanks Guys,

The thread is super educational about real
life experience. My conclussion is like that:
if I am fine with the blade fuses form of
manual disconnecting I can go on and arrange
the board. Still good to be aware about light
voltage that can be enough to trick USB devices
into charging mode.

Thanks a lot to all of you.
Roman
 
I should have added to my post above... the fewer different amperage ratings of fuses or CB's one has in the airplane, the fewer spare parts one has to stock. A Grumman Cheetah I used to fly had its ash tray filled with glass fuses!
 
I should have added to my post above... the fewer different amperage ratings of fuses or CB's one has in the airplane, the fewer spare parts one has to stock. A Grumman Cheetah I used to fly had its ash tray filled with glass fuses!

The Cheetah should have had a spare fuse holder in the glove box with six locations...:)
 
Where did you source these wee beasties? They sound like an interesting compromise perhaps...

Google 'ATC/ATO circuit breaker' and some variations of that. Lots of options floating around. 1st source that popped up for me:
https://www.delcity.net/store/ATO:ATC-Circuit-Breakers/p_823683
but I'm pretty sure you can get them from Amazon.

edit: Remember, because it's a circuit breaker it has yet another pair of contacts that can eventually corrode & fail. One of my 'likes' about using ATC/ATO fuses is one less contact point and a bunch less extraneous stuff affecting the circuit. The only time I've *ever* replaced this type of fuse in a car was when its load actually failed and it did its job of protecting the wire. Anyone who's flown with CB's over a decade or so old has had flaky ones in the panel....
 
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This topic quickly digresses into a religious discussion. We each have our opinions as to how best to achieve circuit protection. To each his own.

Amen. Time to go polish my partially primed airplane....(maybe I'll pull and reset some CBs as well just because I can)....
 
Interesting discussion- ya gotta love VAF!

Very interesting thread- especially hints that my own input early on may represent old-school, out of date thinking! The availability of tough, high-quality wire and connectors does significantly reduce the likelihood of short circuits in well designed installations as they age and opens the door to some cheaper, lighter circuit protection options being discussed here. I’m taking another look at some sections of my current upgrade project with these in mind- could shave a few ounces.

I do see a need for fuse holders designed for clean, visible, accessible in-panel mounting. Anybody know of good ones out there?-Otis
 
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Very interesting thread- especially hints that my own input early on may represent old-school, out of date thinking!

Just as a historical point of order, fuses came before circuit breakers in the evolution of all things electrical.......
 
You can save a lot of weight and panel space compared to breakers. The fuse block can be mounted as a drop-down:

errr, well, theres panel space, and then theres "not otherwise gonna be used" space.....weight, yeah I lose on that one however.....

2q8n9u9.jpg
 
Drop down

The Buss brand fuse blocks are probably the most popular. Example:
https://www.steinair.com/product/12-circuit-fuse-block/

You can save a lot of weight and panel space compared to breakers. The fuse block can be mounted as a drop-down:

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No problem with in-flight access.

P7020009.JPG

This drop down fuse block seems like a good idea for gaining access when needed and being out-of-sight the rest of the time.

Are there any potential problems due to the fuses being inserted from below, i.e. gravity is going to be working against the friction that is holding the fuses upside down in the block?

I wonder what sort of latch holds the tray locked when the fuse block is swung up under the panel.
 
...
Are there any potential problems due to the fuses being inserted from below, i.e. gravity is going to be working against the friction that is holding the fuses upside down in the block?
...
The first time you try to get one of those rascals out, you'll lose all concern about them falling out. They are held in very firmly. I put a drop of ACF50 on mine before I put them in just for a bit of corrosion protection, and they are still hard to remove.
 
This drop down fuse block seems like a good idea for gaining access when needed and being out-of-sight the rest of the time.

Are there any potential problems due to the fuses being inserted from below, i.e. gravity is going to be working against the friction that is holding the fuses upside down in the block?

I wonder what sort of latch holds the tray locked when the fuse block is swung up under the panel.
I'm at 20+ years with just such a set-up in my RV-6. The fuses have always stayed in place. Not definitive just one data point. I used 2 wing-stud camlocks to hold the non-hinged side up. Doing it over, I might consider just using Velcro instead of the camlocks.
 
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Friction and velcro

Thanks Mickey and Randall, I'll try velcro to begin with and can always add a roller spring latch, or similar, later on, if needed.
 
Caution should be exercised whenever considering re-setting a CB or replacing a blown fuse in flight. When I was working (not retired), we couldn’t reset a tripped CB without consulting maintenance (via the radio). In virtually every case, if the flight could be continued safely without a reset, which was always in my experience, we didn’t attempt a reset.

Fuses don’t have to be accessible in flight. It would be helpful if they can become accessible on the ground without too much effort, but replacing a blown fuse, or resetting a tripped CB in flight might create a more serious abnormal or emergency situation. It’s better to figure this out on the ground.
 
Bob N once said, "That tripped circuit breaker just prevented a fire. Why would you want to give the fire a second chance?"
 
For those with fuses - how do you do a preflight?

I’m asking as I’m considering using some Bussmann type units for a dual battery engine bus EFII setup - one bus panel for each “side” of the engine bus. But how do you know a fuse wasn’t blown at shutdown etc? (Unless you use the LED ones, but I assume that means you need power on for your preflight?)

Just rely on the device not working or having fault detection?

If it were a CB it would be obvious. But I like the idea of the compactness and value for money of the fuse blocks.
 
For those with fuses - how do you do a preflight?

I’m asking as I’m considering using some Bussmann type units for a dual battery engine bus EFII setup - one bus panel for each “side” of the engine bus. But how do you know a fuse wasn’t blown at shutdown etc? (Unless you use the LED ones, but I assume that means you need power on for your preflight?)

Just rely on the device not working or having fault detection?

If it were a CB it would be obvious. But I like the idea of the compactness and value for money of the fuse blocks.

You can buy blade fuses that have a blown fuse indicator light built in. Your pre-flight would be a visual scan of the fuse panel after powering the electrical system up. I used two Bussmann modular fuse blocks that I cannibalized and joined together to get the number of positions I wanted. It is panel mounted under my map box and is readily visible at all times. A position legend is in the map box. I am in the camp where a blown fuse or breaker of any critical component requires immediate grounding of the plane, not an in flight CB reset.
 

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I have CBs for essential items like the fuel boost pump, fuses for things I can live without. Sometimes you just get a voltage spike to pop a CB, it's not necessarily your plane trying to burn itself down. But like a recent poster, fuse terminals can corrode and cause their own problems.
 
couple of things to consider;

My avionics guy pointed out that it's nice to have a way to reboot any box that has a CPU without having to shut down the whole system. Could be an avionics switch, an individual on/off switch or a breaker, but fuses would be my last choice if that's the consideration, so in my panel all that stuff is on breakers.

FAR91.205 has some fuse requirements associated with night VFR lighting requirements. i.e. if you're using fuses, you are supposed to carry spare fuses and they are supposed to be accessible in flight.

I'm not saying resetting breakers or swapping fuses in flight is a good idea, I'm just pointing out what the FARs say for certificated airplanes. Take it for what it's worth.
 
You can buy blade fuses that have a blown fuse indicator light built in. Your pre-flight would be a visual scan of the fuse panel after powering the electrical system up.

Thanks.

I was thinking of using a Bussmann or a blue sea fuse block on the firewall side to act as a buss for engine electronics. But a preflight would be totally impossible in this case as you would need to remove the cowls and power the aeroplane up to make sure nothing was blown at the last shutdown. And having them visible negates the point - of not having 2 large power cables going from the battery into the cockpit.

Maybe cb’s are better in this case. But it ends up being a lot of cb’s just for the engine electronics. A bit confused on the best way to proceed.
 
Breaker Breaker

Anyone who's flown with CB's over a decade or so old has had flaky ones in the panel....

AND: "Bob N once said, "That tripped circuit breaker just prevented a fire. Why would you want to give the fire a second chance?"

As this is truly a religious matter, I'm not going to advocate for one or the other, fuses/CBs. To me it seems that it is just a trade off of on one hand going cheaper and lighter, and on the other hand having the ability to quickly see what tripped, be able to easily disconnect/turn off a load (like a run away AP), and be able to re-set it under certain conditions. You choose which approach is more important to you, neither is absolutely better than the other.

That said, let me address the two quotes above from my personal experience:

1)Though I've heard of it, I have never had a flaky Klixon CB flying with 30 of them for 25 years now. Never.

2)Give the fire a second chance? Catchy phrase, but no reality to it. The CB will just trip a second time.

As already mentioned, there are transient conditions that may warrant a reset. And in other cases, may be of diagnostic value. I had the main alternator field breaker trip shortly after lifting off Teterboro, a real attention getter, and it did stay in again for some time after resetting. Apparently an intermittent problem that re-appeared I finally flew home on the Aux alternator...
 
The RV-12iS uses fuses - see the center console. So Van's is comfortable with them in at least some locations for some purposes. The RV-12iS does not have breakers, as far as I know.

RV-12iS_Panel.jpg


Dave
 
Typically in the airlines you are allowed to reset a circuit breaker ONE TIME. Sometimes they do trip for no apparent reason.
 
Endless debate over the years.
I have never had a fuse blow for no reason in any application. I have had more than my share of flaky circuit breakers, but generally they are very reliable.
I like fuses for most applications. Low cost, light weight, small footprint, don’t take up any panel space unless you want them visible (I don’t), heightened fault current, typically faster circuit interrupt, vibration proof, etc…. dumb and simple like me….
I also have no issues with circuit breakers and would t fault anyone for using them. I have one circuit breaker, pull type, for Alt. Field. My fuse blocks are under the panel, out of sight. 16 years, 900 hours, never had one blow. They are also mounted upside down. Stien helped me with that decision. They won’t “fall out” even hanging upside down, but get looked at every CI.

You also have another choice that is becoming more common. Piezoelectric. Basically fuses that don’t need to be replaced, or a breaker that automatically resets when a fault clears. They also allow manufacturers like Vertical Power to integrate them into relatively sophisticated controls, power handling, and annunciation, all in one tidy “box”. However, unlike simple fuses or breakers, if you have a gremlin to chase, it can be daunting.
 
Get AeroElectric Connection

A bit confused on the best way to proceed.
... like all of us are, or at least were at some point.
I recommend starting with Bob Nuckolls' Aeroelectric Connection, which gives a good grounding in this stuff including pros and cons of CBs and fuses.
And search this forum for the various threads, there are many (Hint: use Google e.g. site:vansairforce.net fuses rather than the VAF search).

Personally I put a few things (like, 6) on breakers - things I wanted pullable or to have an immediate indication of a fault. The rest (like, 25) on spade fuse blocks on a drop down panel. 23 years later, I'm still happy with the arrangement.
 
Typically in the airlines you are allowed to reset a circuit breaker ONE TIME. Sometimes they do trip for no apparent reason.

Yes and no, a little more complex than that. One reset for safety critical systems. For example, reset the landing gear CB once. If it pops again, emergency landing gear extension, mayday on the radio, fire trucks and all the excitement.

If the GPS CB pops in flight, use the other GPS if equipped, or do a conventional approach at destination. Reset on the ground with maintenance awareness.

Some airliner CBs aren't accessible in flight. It's almost as if the designers didn't want us resetting them. I plan the same logic with my plane. Fuses for some systems, and put them somewhere I'm not tempted to fiddle with in flight. CBs for ones that might need to be pulled or reset in flight.
 
.....I have never had a fuse blow for no reason in any application. I have had more than my share of flaky circuit breakers, but generally they are very reliable......

that comments rings true for me

On this debate, my current thought settles on breakers for pretty much everything though
because I like the idea of being able to preflight easily that nothing is faulted before and after start-up
and so that I can see it if faults in flight
 
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