Why does the breaker pop?

[Chrisgoesflying]

I noticed something during my past two flights, which both finished after sunset, but still during civil twilight. Obviously, after sunset, I have all my lights on. However, when I turn on all the lights, some breaker always trips. A few days ago, the fuel pump breaker tripped. Today, the nav light breaker tripped. It seems like I can't have everything on at the same time, otherwise, one of the electrical parts will go offline. It's not always the same one, but I kind of don't want to play that game to find out it's the gear one day, for example. What could cause this? Obviously, during daytime flights this isn't an issue. I don't need my interior lights. But, with days being so short, I do end up in the dark every now and then and would like to have all my lights available.

 

[PaulMillner]

I noticed something during my past two flights, which both finished after sunset, but still during civil twilight. Obviously, after sunset, I have all my lights on. However, when I turn on all the lights, some breaker always trips. A few days ago, the fuel pump breaker tripped. Today, the nav light breaker tripped. It seems like I can't have everything on at the same time, otherwise, one of the electrical parts will go offline. It's not always the same one, but I kind of don't want to play that game to find out it's the gear one day, for example. What could cause this? Obviously, during daytime flights this isn't an issue. I don't need my interior lights. But, with days being so short, I do end up in the dark every now and then and would like to have all my lights available.

If there’s corrosion between your breakers and the bus bar, the resultant resistance heats the bus and the adjacent breakers. Since the breakers are thermal, they pop.

Pull the attachment screw, clean away any corrosion, spray with ACF50 or CorrosionX, then retorque carefully. Or, when this happens, gingerly touch the bus to check for heat… don’t burn your finger tip.

Paul

 

[Bell206]

What could cause this?

Has this been an ongoing problem or something new?

Have you added any additional electrical equipment prior to this issue?

Do you know the amp rating of your altenator?

How old and condition of aircraft battery?

Since its a different breaker each time it can be a number of things. But my first guess would be at the electrical distribution. Could be as simple as a corroded ground connection to an alternator load issue.

Have seen similar problem where the inrush of load on a single circuit would trip the "weakest" CB. But there wouldnt be any issue with that specific system.

Perhaps give the entire electrical system a once over for anything obvious. If nothing check system voltage and load levels during ground run as you turn on each system.

Tough to make a call without more info. Just be sure to check all the main ground connections for the alternator and battery.

If nothing stands out may also want to start looking for voltage drops on both positive and negative sides.

 

[Chrisgoesflying]

Has this been an ongoing problem or something new?

I don’t know. I never turned on all my lights and electrical items until last week. It works fine if I leave one item off. It only pops if I turn everything on.

Do you know the amp rating of your altenator?

Nope. But can probably find out easily.

Have you added any additional electrical equipment prior to this issue?

Nope.

How old and condition of aircraft battery?

Older but in good condition.

 

[Jeff767]

Check all your grounds for corrosion particularly the engine and alternator grounds. Each should probably be removed and cleaned.

 

[Bell206]

I never turned on all my lights and electrical items until last week.

What specific model aircraft and year?
Is this aircraft new to you?
Trying to understand why you never had everything turned on before.

It only pops if I turn everything on.

Do you have an Amp indicator or a load indicator installed?

How did this indicator react while turning on the electrical systems? Any spikes with the needle?

Does it have a voltmeter as well? Does the voltage remain steady as you increase the load? Or does hit hunt at each switch you turn on?

 

[Chrisgoesflying]

What specific model aircraft and year?

1960 Piper Comanche 250.

Is this aircraft new to you?

Somewhat. Bought it in May. Flown it for about 50 hours so far.

Trying to understand why you never had everything turned on before.

Because I never flew it at night and during the day I don’t need my interior lights. The previous two flights were my first ones that extended to after sunset since I bought this plane.

Do you have an Amp indicator or a load indicator installed?

How did this indicator react while turning on the electrical systems? Any spikes with the needle?

Does it have a voltmeter as well? Does the voltage remain steady as you increase the load? Or does hit hunt at each switch you turn on?

It has this thing that tells me if the battery is charging, depleting or is neutral. I didn’t look at it when the breaker popped. The first time, when the fuel pump breaker popped, I didn’t even notice it until the next flight when I did my routine breaker check. Yesterday, the interior light breaker popped when I turned on the landing lights. I was already in the landing phase so I didn’t look at the amp thing.

 

[Bell206]

Somewhat. Bought it in May. Flown it for about 50 hours so far.

Well since this new to you also, may want to take a step back and have things looked at. The plane is telling you something and you should listen to it.

I cant download any manuals at the moment and without more specifics cant really offer more at the moment. Perhaps perform some ground runs and watch the ammeter and voltmeter and see how they react to electrical loads you put on it?

Regardless, you probably will need to get your AME involved as my guess is you have some elec system condition issues or possibly an alternator regulation or load handling issue or both when a full elec load is applied.

Once I can see a manual might be able to offer more. I read you have a big trip coming up so maybe have your mechanic look at the big stuff and come up with a plan to minimize any issues on the trip?

Is the avionics, lights, etc factory or are they 3rd party upgrades?

ARe there any avionics/electrical upgrades listed in the aircraft records? 337s?

 

[Checkout_my_Six]

Something is heating the bus bar and causing those breakers to pop. Are these all with in the same area on the bus bar?

My vote is a bad connector ...maybe the alt cable?...is arcing ....causing heat on the bus bar.

 

[Chrisgoesflying]

@Bell206 We're already on the long trip and a long way from home. My mechanic looked at the plane prior to departure. We both did an extensive annual. Everything checked out nicely. I had the plane parked outside for a few weeks as I moved and didn't have a hangar. That was the only anomaly since the October annual as I usually always have the plane inside a hangar. One thing I noticed while I had the plane parked outside was, the metal on my brake handle became somewhat rusty (it was really humid during those four weeks the plane was outside) which it never did while parked indoors. I cleaned that up, applied some rust inhibitor and that solved it until my new hangar became available. However, maybe during that time, something down at the electronics also got rusty?

@Checkout_my_Six Yes, the two breakers that popped (fuel pump and interior lights) are next to each other. I see you're in MD. Where exactly? We're in MD right now as well for the night taking a break on our way to Florida. Never been to this state but really like it here, at least here on the coast where we are.

 

[Checkout_my_Six]

[USER=2092]@Checkout_my_Six Yes, the two breakers that popped (fuel pump and interior lights) are next to each other. I see you're in MD. Where exactly? We're in MD right now as well for the night taking a break on our way to Florida. Never been to this state but really like it here, at least here on the coast where we are.

FDK Frederick MD....

If you are able to look behind the panel at the circuit breakers....look for a burnt or browning wire. I bet it's your alternator wire...where it attaches to the bus bar. Your mechanic should be able to cut back a few inches into good wire and re crimp a new connector. BTW...it's the largest wire there.

 

[Chrisgoesflying]

FDK Frederick MD....

If you are able to look behind the panel at the circuit breakers....look for a burnt or browning wire. I bet it's your alternator wire...where it attaches to the bus bar. Your mechanic should be able to cut back a few inches into good wire and re crimp a new connector. BTW...it's the largest wire there.

Oh, far from where we are. We're in Ocean City right now.

 

[geezer]

Post 2 and 9 have my vote.

Bad connections from loose or corroded heating the buss bar are almost certainly the cause.

Cleaning and re torqueing them should correct the problem. Your mechanic should perform this work, but preferably with your assistance, if he is willing. Many very good mechanics decline to have the customer around so do not be offended if he declines.

 

[Chrisgoesflying]

Post 2 and 9 have my vote.

Bad connections from loose or corroded heating the buss bar are almost certainly the cause.

Cleaning and re torqueing them should correct the problem. Your mechanic should perform this work, but preferably with your assistance, if he is willing. Many very good mechanics decline to have the customer around so do not be offended if he declines.

My mechanic will absolutely allow me to be around when performing this work. I always do owner assisted annuals and he encourages that with all of his customers so the pilots know as much about their planes as possible. The problem is, I'm far from home at the moment and should get this fixed ASAP so I will most likely end up having a mechanic I don't know fix the issue.

 

[ateamer]

The landing light fuse on my RV-8 blew three times. The cause turned out to be the switch. The plane was built with less-than-aviation-grade toggle switches, and the terminal on the back of the switch had worn excessively. Instead of screw-on terminals, these had slide-on connectors, which are fine - but. But, the cheap ones have the terminals fastened to the switch body with hollow rivets. Over time, heat cycles loosen the rivets, which leads to arcing.

After replacing the switch with a better one, no problems. Replacing all the switches with Honeywell switches is on the white board.

Not at all uncommon in the experimental world to use the auto parts store switches. I don’t get why someone would spend 50 to well over a hundred grand building a plane and then cheap out on one of the most fiscally inconsequential parts of the project.

 

[unsafervguy]

The landing light fuse on my RV-8 blew three times. The cause turned out to be the switch. The plane was built with less-than-aviation-grade toggle switches, and the terminal on the back of the switch had worn excessively. Instead of screw-on terminals, these had slide-on connectors, which are fine - but. But, the cheap ones have the terminals fastened to the switch body with hollow rivets. Over time, heat cycles loosen the rivets, which leads to arcing.

After replacing the switch with a better one, no problems. Replacing all the switches with Honeywell switches is on the white board.

Not at all uncommon in the experimental world to use the auto parts store switches. I don’t get why someone would spend 50 to well over a hundred grand building a plane and then cheap out on one of the most fiscally inconsequential parts of the project.

simple answer. good quality switches look like switches always have. the auto world has a lot of cool looking switches that are questionable quality but look real cool. the experimental world has shifted to add every option and look like a high end automobile, at the cost of weighing a ton and handling like a mack truck.

 

[ateamer]

simple answer. good quality switches look like switches always have. the auto world has a lot of cool looking switches that are questionable quality but look real cool. the experimental world has shifted to add every option and look like a high end automobile, at the cost of weighing a ton and handling like a mack truck.

Plus heavy, expensive upholstery and avionics. I understand that the building and modifications are the goal for many. I like lightweight, snappy handling and climb rate, and less buttonology and “what’s it doing now”. If I was building, it’d be an RV with a single com, portable GPS, and whatever gauges/instruments are lighter and don’t have moving parts and have less plumbing, probably a G5 and basic engine monitor, no upholstery beyond basic fabric seats, no autopilot.

 

[Dan Thomas]

Yes, the two breakers that popped (fuel pump and interior lights) are next to each other.

If you are able to look behind the panel at the circuit breakers....look for a burnt or browning wire. I bet it's your alternator wire...where it attaches to the bus bar.

Breakers are thermal devices. There is a bimetal strip in there. It's made of two different metals that have different coefficients of thermal expansion. They have some electrical resistance. Thin strips of each metal are bonded together and pressed into a concave shape so that as the current through them rises, the bonded assembly bends and eventually snaps into a convex shape, lifting the contact bonded to it off the other, fixed contact, interrupting the flow. The button pops out, pushed by a light spring, and the inside end of it gets between the contacts so that the breaker won't just reset itself. The breaker cannot be reset until that strip cools down and pops back into shape and gets out of the way of the button. Trip-free breakers, they're called.

So heat from oxidized breaker contacts will add resistance, so the strip gets hot sooner and will pop off easier.

Oxidized crimp terminals add resistance, too, between the copper wire and the terminal, and between the terminal and breaker terminal. More heat that can pop it off sooner. As Checkout says, look for a terminal discolored by heat.

Oxidized breaker terminals at the bus strip, or their screws, can introduce resistance and heating, as noted in an earlier post.

Breakers are stuffed almost against each other behind the panel. One bad one can heat the others on either side of it, predisposing them to pop off sooner, or for no apparent good reason.

1960. Good chances that most of the original breakers are still in there. I would expect troubles. Time lets oxygen combine with metal surfaces to form resistive oxides. Nothing lasts forever, and airplanes rot whether they're flown or not.

 

[unsafervguy]

Plus heavy, expensive upholstery and avionics. I understand that the building and modifications are the goal for many. I like lightweight, snappy handling and climb rate, and less buttonology and “what’s it doing now”. If I was building, it’d be an RV with a single com, portable GPS, and whatever gauges/instruments are lighter and don’t have moving parts and have less plumbing, probably a G5 and basic engine monitor, no upholstery beyond basic fabric seats, no autopilot.

thats the way to do it, my rv-4 has a 360, constant speed, skyview and is under 1000 lbs

 

[Checkout_my_Six]

Dan....heat is the problem....not from circuit that's popped....but from a neighbor heating the bus bar. The breakers popping are near this heat source.....and there is an arcing wire in a bad connector. Been there....seen it. Increase the load of the bus bar and the bad neighbor makes more heat....and the popping begins.

 

[PaulMillner]

Do you know the amp rating of your altenator?

Nope. But can probably find out easily.

Hmmm. Your airplane came from Piper with a generator, not an alternator. Whose alternator retrofit kit was installed? What's the make of alternator?

Rising above that, the alternator is not the problem... it's heat at the bus bar, whether due to aged breakers, corrosion, bad wire crimps... invasive (take it apart) inspection may be required if a glance doesn't tell the story.

Paul

 

[Chrisgoesflying]

I think the bad actor is the interior lights. I put it on full load today sans the interior lights and nothing popped. As soon as the interior lights come on something pops. I touched the bus bar and it wasn’t hot. Just warm. Not sure if it is supposed to be warm.

 

[Salty]

How thick and wide is the bus bar? Maybe it’s not big enough to handle the load.

 

[Ed Haywood]

When I recovered my aircraft, I intended to save $$ by reusing electrical components. After seeing what 45 year old electrical stuff looks like, and the rats nest of old wiring from previous alterations, I gutted and replaced the entire system. Every switch, breaker, bus, terminal, and wire. I did reuse the radio and transponder harnesses, which were done by a good avionics shop in the last 5 years.
I realize that is a much more involved project in a metal aircraft, but TBH I am surprised it is not considered more often. The cost of parts is cheap, maybe $500 max. Labor is more, but that can be controlled by the owner working under supervision. A more limited scope effort with high payoff would be replacing the bus, switches, and breakers.
Electrical work does not require special skills and tools, just basic knowledge and a willingness to go slow and follow best practices. Do it right and you can spend the next 20-30 years flying instead of chasing gremlins.

 

[Dan Thomas]

Dan....heat is the problem....not from circuit that's popped....but from a neighbor heating the bus bar. The breakers popping are near this heat source.....and there is an arcing wire in a bad connector. Been there....seen it. Increase the load of the bus bar and the bad neighbor makes more heat....and the popping begins.

Isn't that what I said? The heat doesn't even require arcing. You'd smell that. It just requires resistance, usually from oxidation or some other form of corrosion. I've been there and seen it multiple times as a mechanic.

 

[Checkout_my_Six]

I think the bad actor is the interior lights. I put it on full load today sans the interior lights and nothing popped. As soon as the interior lights come on something pops. I touched the bus bar and it wasn’t hot. Just warm. Not sure if it is supposed to be warm.

No....it shouldn't be warm. Turn everything on with the engine running....including pitot heat. Then feel it. You may burn yourself. careful. When you find the source of the heat you've located the problem....

 

[Checkout_my_Six]

How thick and wide is the bus bar? Maybe it’s not big enough to handle the load.

It's a copper bar.....it's big enough.

 

[StraightnLevel]

No....it shouldn't be warm. Turn everything on with the engine running....including pitot heat. Then feel it. You may burn yourself. careful. When you find the source of the heat you've located the problem....

The easiest way to find an abnormal heat source is to use a thermal camera. IR scanning is commonly used for heavy electrical gear to find loose connections and undersized conductors. Turn everything on to generate full load, then aim the camera at everything electrical until you find the hot spot. If you don't find one, you may just need to replace the old breakers (though the OP description doesn't sound like a breaker at EOL).

IR cameras can be rented for this purpose.

 

[StraightnLevel]

It's a copper bar.....it's big enough.

Bad assumption. EVERY conductor has a loading limit, and every conductor generates resistive heating in operation.

The underlying issue could be a significant resistive fault that has increased the total load to the point that the bar is heating. Unlikely, perhaps, but that sort of fault can and does occur. Without looking at individual circuit loads and/or heat scans, you can't assume anything about the load.

 

[Checkout_my_Six]

Bad assumption. EVERY conductor has a loading limit, and every conductor generates resistive heating in operation.

The underlying issue could be a significant resistive fault that has increased the total load to the point that the bar is heating. Unlikely, perhaps, but that sort of fault can and does occur. Without looking at individual circuit loads and/or heat scans, you can't assume anything about the load.

Yup....but I know the Comanche. His is similar to this one.

 

[Dan Thomas]

Bad assumption. EVERY conductor has a loading limit, and every conductor generates resistive heating in operation.

You are not an aircraft mechanic. There are legal limitations to how much resistance is permissible in any aircraft conductor. AC43.13 spends a lot of time on it. A short, thick copper bus bar should not even get warm.

 

[JAWS]

Ever wonder why good/expensive pots and pans have copper bottoms?
They transfer heat well.
Copper also transfers electrons very well.
A bad switch or circuit breaker can transfer the heat generated down the copper bus bar to another spot.
Look for the hot spot.

 

[Dan Thomas]

From AC43.13-1B, Chapter 11:




How often does that happen at annual?

 

[Albany Tom]

Not an a&p, but do have experience troubleshooting electrical systems. Agree with everyone that's thinking it's likely heat related to the bus, re bad connection. One thing I didn't see mentioned, that I don't know if applies to aviation breakers, is that thermal breakers, in general, have a reputation for sometimes "light tripping" if they've been overloaded a lot. The theory being that the motion that Dan described above, if it happens a lot, can cause the spring to be less of a spring.

I don't know if this is true, or if it's applicable to aviation breakers. I am sure, though, that it would be a secondary issue not the primary cause. Just bringing it up in the case you find and fix the problems, but some breakers still trip once in a while that didn't used to. *IF* aviation breakers work like industrial breakers, a 20A breaker should pass 20.00A forever and not trip. Breaker manufacturers publish charts of overload vs time for different models. I'm willing to bet the specs are different for aviation and non-aviation, so take all of this with a grain of salt.

 

[PaulMillner]

thermal breakers, in general, have a reputation for sometimes "light tripping" if they've been overloaded a lot. The theory being that the motion that Dan described above, if it happens a lot, can cause the spring to be less of a spring.

[/QUOTE]
That's definitely a thing in aviation... the breakers aren't special, you can find them on Mouser or Digikey. The only thing "special" in some cases is the terminal orientation, and that's just a different dash number to the commonly available breaker. Of course, some breaker manufacturers (and breaker lines) have gone away over time, requiring substitution. But general electrical engineering principles apply to aircraft just like they do to the rest of the work.

a 20A breaker should pass 20.00A forever and not trip. Breaker manufacturers publish charts of overload vs time for different models. I'm willing to bet the specs are different for aviation and non-aviation, so take all of this with a grain of salt.

Nope, same breakers, same time versus overcurrent curves. And the OEMs take advantage of that at times. For instance, Cessna 60 amp alternators are sometimes paired by Cessna with 50 amp breakers, because they know the alternator won't output 60 amps for long enough to meet the trip point on the curve (only during initial heavy battery charging after start). Or, the gear pump on my Cardinal that pulls ~55 amps is fitted to a 35 amp breaker, because the pump normally only runs 14 seconds at a time... not nearly long enough to get to the trip point on the curve. If it *does* run longer, then something is wrong, and the breaker tripping might be a good thing.

Paul