Circuit breaker size for LED lights

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CA182R

Pre-takeoff checklist
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CA182R
Looking at recent posts on LED lights and considering how less power they consume compared to the originals, it's making me wonder whether downsizing their associated circuit breakers would provide any benefits. Let's say going from 10A original circuit breaker to a 2A for a LED landing/taxi light circuit breaker (0.7A each LED light). I'm assuming it wouldn't but curious about any thoughts.
 
CA182R said:
Looking at recent posts on LED lights and considering how less power they consume compared to the originals, it's making me wonder whether downsizing their associated circuit breakers would provide any benefits. Let's say going from 10A original circuit breaker to a 2A for a LED landing/taxi light circuit breaker (0.7A each LED light). I'm assuming it wouldn't but curious about any thoughts.
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I'm told the breaker/fuse is sized to protect the wiring ...
 
Bell206 said:
FYI: circuit protection devices protect the wires not the component.
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But there is no reason a circuit breaker can not be sized smaller than the wires it protects. It only protects even better and may provide some amount of device protection as well. As long as there is the correct log book modification, nothing prevents a 2 amp breaker from protecting wires that can handle 10 amps. It is done all the time with long wire runs outside of aviation - you oversize the wires to prevent voltage drop, but don't oversize the breaker because it is not necessary for the load on the circuit.
 
So, for the particuar scenario of the LED taxi and landing lights with 0.7A draw for each light, the circuit breaker for both lights could be let's say 2A to 5A, or even higher depending on the rating of the wires to the lights?

Cessna SEB09-6R1 calls for the inspection and replacement of the light switches with ones of higher amp rating. Now, I understand that replacing the lights with LEDs does not remove the need to replace these light switches, especially if keeping the old higher rating breaker.
 
Matthew Rogers said:
But there is no reason a circuit breaker can not be sized smaller than the wires it protects.
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Not at all. My FYI was merely to correct OPs use of the device/consumer to determine the CB rating vs the wires. The wire size is usually selected first depending on circuit length, load, etc. and the circuit protection selected second.
 
Bell206 said:
FYI: circuit protection devices protect the wires not the component.
Click to expand...
That's true (mostly) for house wiring. However, in the case of aircraft, the goal is to protect the rest of the aircraft from an overload in either the wiring or the load.
It's got little to do with the amount of current actually NEEDED to power a load but rather what the load and the wiring is rated to handle. Since these things are designed as retrofit for higher amperage devices, I would suspect that they are rated for the device they're intended to replace.
 
If a component shorts internally, it's already damaged. A breaker isn't going to save it. The concern is that the short, or any short along the wire, will get that wire red-hot and start a fire or do damage to other wires in the bundle. That's what breakers are for.

I'd leave the breakers as they are. If that LED light pooches somewhere away from home, and the only available replacement is an incandescent light, you're still OK to go.
 
I reduced mine, but I happened to have a handful of switch-breakers left over from my panel projects.
 
flyingron said:
That's true (mostly) for house wiring. However, in the case of aircraft, the goal is to protect the rest of the aircraft from an overload in either the wiring or the load.
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System design determines the wire size and load. CBs or fuses are selected to protect that wiring as stated in most guidance. Here’s one below but there are others. As to retrofit, since any change to the TC'd basic electrical system design can be considered a major alteration its actually a case by case determination.

11-51.CIRCUIT BREAKER USAGE.Circuit breakers are designed as circuit protection for the wire (see paragraph 11-48and 11-49), not for protection of black boxes. Use of a circuit breaker as witch is not recommended. Use of a circuit breaker as a switch will decrease the life of the circuit breaker.
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43.13-1B_Full.pdf
 
CA182R said:
Looking at recent posts on LED lights and considering how less power they consume compared to the originals, it's making me wonder whether downsizing their associated circuit breakers would provide any benefits. Let's say going from 10A original circuit breaker to a 2A for a LED landing/taxi light circuit breaker (0.7A each LED light). I'm assuming it wouldn't but curious about any thoughts.
Click to expand...

Assuming the wires are already rated for much higher than 10A, breaking the circuit at 2A will not provide any benefit. You might gain a fraction of an ounce in useful load if the 2A fuse is lighter than the 10A fuse, but that's about it.
 
sarangan said:
Assuming the wires are already rated for much higher than 10A, breaking the circuit at 2A will not provide any benefit. You might gain a fraction of an ounce in useful load if the 2A fuse is lighter than the 10A fuse, but that's about it.
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Until the wire is 50 years old and has partially worn through, partially cracked, or crushed in size and is no longer actually rated for 10A. If you are replacing the wire, then it and the breaker can be properly and similarly sized. If just replacing the breaker, (other than issues with a sign-off) replacing it with one of lower amperage can only serve to lessen the chances of a failure due to crappy old wiring (most of the GA fleet). Lower amps means less potential heating, fires, etc in the case of a damaged wire or overloaded system. I would rather have a breaker pop, than the wire get hot and smoke or catch fire. If there is an opportunity to do so (legally per the regs), why not do so? It doesn't hurt and may save an in-flight fire.
 
Matthew Rogers said:
Until the wire is 50 years old and has partially worn through, partially cracked, or crushed in size and is no longer actually rated for 10A. If you are replacing the wire, then it and the breaker can be properly and similarly sized. If just replacing the breaker, (other than issues with a sign-off) replacing it with one of lower amperage can only serve to lessen the chances of a failure due to crappy old wiring (most of the GA fleet). Lower amps means less potential heating, fires, etc in the case of a damaged wire or overloaded system. I would rather have a breaker pop, than the wire get hot and smoke or catch fire. If there is an opportunity to do so (legally per the regs), why not do so? It doesn't hurt and may save an in-flight fire.
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The breaker is there to cut off the current in an overloaded system or the shorting to ground of a damaged wire. You can't get a wire hot if the system is properly designed, assembled and maintained. Old breakers will pop early, not late. Pilot-induced fires happen when he puts in a heavier fuse, or wraps the burned-out fuse in tinfoil. No amount of new wiring will prevent such stupidity.

AC43.13-1B has extensive guidance on all of this. For instance, the current limits on wires goes down as they get longer, and if they are in bundles rather than in free air. Your airplane's system will have been designed as per those instructions.

As I said, the existing landing/taxi light wiring was gauged for incandescent lights. Sure, the LED doesn't need that capacity, so one might install a smaller breaker and even smaller wire, but what happens if the next owner puts incandescent lights back in it? The breaker will pop. His mechanic will install the "correct" breaker as per the parts catalog, and now he WILL have an electrical fire with that small wiring.
 
As many others have said, the fuse/breaker is there to protect the wiring and not the component. It's the sacrificial lamb, the designated weakest point in the chain. As long as it is properly sized to trip/blow BEFORE the associated wiring is overloaded, there is no real benefit to downsizing the breaker. If LEDs are installed on the same wiring(heavier than needed) there is no additional need to protect the wiring.

Someone brought up the issue of aging/damaged wiring; if the wiring is that old and/or damaged, it needs to be replaced, not the breaker. If any section of wiring gets damaged or worn to the point of reduced load capacity below the breaker rating, it then becomes the fuse. Bad things happen when wires become fuses.
 
I don’t know if it fits the topic, but I will still ask. I was just looking for some good LEDs for my room.
 
I replaced all the old breakers in my plane, the original cessna ones are not pullable. I really like being able to shut off a circuit should I choose to.
 
Old wiring is was designed for incandescent lights/motors that had a large initial inrush of current as the the wiring was basically 0 or a few ohms when turned on. Fuses/cbs were 'derated' by a multiplier to account for this.

With LEDs this is not an issue anymore as built in regulators limit the voltage.

So not only do you not need the same wire size, you don't even need the same amp rating. in a certificated airframe changing the cb would be a minor alteration so if you can get an A&P to sign it off go for it.

You might fly .01kts faster since you reduced the load on the alternator.
 
pfarber said:
Old wiring is was designed for incandescent lights/motors that had a large initial inrush of current as the the wiring was basically 0 or a few ohms when turned on. Fuses/cbs were 'derated' by a multiplier to account for this.

With LEDs this is not an issue anymore as built in regulators limit the voltage.

So not only do you not need the same wire size, you don't even need the same amp rating. in a certificated airframe changing the cb would be a minor alteration so if you can get an A&P to sign it off go for it.

You might fly .01kts faster since you reduced the load on the alternator.
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It's always amusing when someone opines on a subject that they have no knowledge of.
 
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Despite the fact that the 43-13 is full of good info, it's worth keeping in mind that it is not a design guide, it is a repair document.

There are other documents out there that clarify one or two points few a little better IMO.
Per https://www.sae.org/standards/content/arp1199b

overcurrent protection is recommended every place you step down in wire size. Single phase breakers protect the wire and the current source. You don't want a shorted wire to cause the master breaker to trip while you are IFR. I wouldn't put a continuous load on a breaker that's more than 80%. If breakers cascade, you want the breakers closest to the load to trip first. You want the breaker on the power source end of the wire not the load.
 
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There is a lot more out there.

My day job is working at an avionics engineer for an airline. It pays for my 100LL habit. At an airline, the Engineering department is primarily responsible for configuration control of the aircraft. I was an airline A&P before I got my bachelors in electrical engineering. I don't design anything. We aren't trying to be super mechanics, despite the impression mechanics have. We have them for the mechanical work. I work in a 24x7 maintenance support center. From where I sit I can read almost everything that's recorded about the Mx on a fleet of about 400 airliners world wide.

When you work for a properly funded engineering group, typically the company pays for access to specification databases. We use Information Handling Systems (IHS). They provides us an online library of specifications which also includes an e-book library with hundreds of design text books on titles you really don't find anywhere else. Seriously, where else would you find a downloadable copy of. "Aviation weather surveillance systems - advanced radar and surface sensors for flight safety and air traffic management"?

In addition, when the airline is a member of ARINC and RTCA, you have access to all of their specs too. When you operate Boeing and Airbus aircraft, you also have access to limited specifications, drawings and their customer specific data too. There are Non-disclosure agreements in place that prevent me from sharing most of that info.

RTCA specs affect everyone trying to get a TSO. ARINC members are airliner OEMs and operators. GAMA represents GA on new aircraft.

For GA there are GAMA standards and honestly, when there is overlap, I can't tell you how an ARINC 429 data bus differs from a GAMA 429 data bus. It could be relevant though.
See -> https://gama.aero/facts-and-statist...ry-technical-publications-and-specifications/

When I bought an airplane, it was a mess electrically, despite the fact that the paperwork looked in order. When I decided to fix it all, I started looking for design references. I found surprisingly little outside of the 43-13 Advisory Circulars and they are really limited.

I also belong to a social networking group somewhat like POA for engineers. Like POA, anyone can read the information posted, they would rather not have any non-engineers posting questions.

See-> https://www.eng-tips.com/

Over the years I've posted questions about circuit breakers, aircraft wiring questions, splice reliability questions etc. One of the folks in there is an aerospace designer that's been active for a lot of years, I'm not sure if he works on the military or civilian side.

He shared the following list of documents to look at with regard to circuit breakers, if you are interested. Installed circuit breakers look simple, but a lot has been written about them with regard to aircraft over the years.

Here is his somewhat dated list. It's probably incomplete.
FAA AC25.13567-1 Circuit protective devices.
FAA AC25-16 Electrical Fault and Fire Prevention and Protection
FAA AC43-206 Inspection, Prevention, Control, and Repair of Corrosion on Avionics Equipment
SAE ARP1199, DEVICES, ELECTRIC OVERCURRENT PROTECTIVE, SELECTION, APPLICATIONS, AND INSPECTION OF
SAE ARP4101/5 Aircraft Circuit Breaker and Fuse Arrangement
SAE ARP4404 Aircraft Electrical Installations
SAE AS50881 WIRING, AEROSPACE VEHICLE
SAE AS58091 Circuit Breakers, Trip-Free, Aircraft General Specification For
SAE J553 Circuit Breakers
SAE/TP 2006-01-2419 Arc Fault Protection, Application Techniques for Aircraft Circuit Breakers
MIL-DTL-27715 CIRCUIT BREAKER, TRIP-FREE, HIGH TEMPERATURE, AIRCRAFT GENERAL SPECIFICATION FOR
MIL-DTL-23928 PANELS, ELECTRICAL, POWER DISTRIBUTION AND MANUAL TRANSFER, CIRCUIT BREAKER TYPE
MIL-HDBK-522 GUIDELINES FOR INSPECTION OF AIRCRAFT ELECTRICAL WIRING INTERCONNECT SYSTEMS
MIL-HDBK-5400 ELECTRONIC EQUIPMENT, AIRBORNE GENERAL GUIDELINES FOR
MIL-STD-7080 SELECTION AND INSTALLATION OF AIRCRAFT ELECTRIC EQUIPMENT
WRDC-TR-90-4075 FAILURE ANALYSIS TECHNIQUES FOR THE EVALUATION OF ELECTRICAL AND ELECTRONIC COMPONENTS IN AIRCRAFT ACCIDENT INVESTIGATIONS
WL-TR-95-4004 AIRCRAFT MISHAP INVESTIGATION HANDBOOK FOR ELECTRONIC HARDWARE
DOT/FAA/AR-01/118 Aircraft Age-Related Degradation Study on Single- and Three-Phase Circuit Breakers
USAF T.O. 1-1-686-1, CLEANING AND CORROSION CONTROL VOLUME I CORROSION PROGRAM AND CORROSION THEORY
USAF T.O. 1-1-686-3, CLEANING AND CORROSION CONTROL VOLUME III AVIONICS AND ELECTRONICS
USAF T.O. 1-1-686-5, CLEANING AND CORROSION CONTROL VOLUME V CONSUMABLE MATERIALS AND EQUIPMENT FOR AVIONICS
USAF T.O. 1-1A-14 INSTALLATION AND REPAIR PRACTICES VOLUME 1 AIRCRAFT ELECTRIC AND ELECTRONIC WIRING

There are other specifications bodies out there. The FAA has been using American Society for Testing and Materials (ASTM) to define the requirements for a lot of the small aircraft Part 23 requirements. See -> https://www.faa.gov/aircraft/air_ce...es/small_airplanes_regs/media/part_23_moc.pdf

In one of the most depressing EAA meetings I went to, 5-6 years ago, the FAA rep was talking about ASTM specs now being the standard. He didn't even know what ASTM stood for or who they were.

I don't have these at work, I did buy one ASTM - F2490 - 20 to see what a real Electrical Load Analysis for a GA airplane should look like. The comment, "Electrical Load Analysis within limits." on the 337s for my airplane looked good to someone but, were meaningless.
Hope this helps put it in perspective.
 
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In response to a side conversation:
There are different standards for different things.

There are regulatory standards set for certification approval.
There are standards set for compatibility and interchangeability.
ARINC & GAMA standards improve ability for interchangeability to promote commercial competition among vendors and reduce original airframe construction costs.
I see 43-13-1 as repair craftsmanship standards much like a Boeing SWPM or an Airbus ESPM.
Some standards like TSOs and MIL specs just define what characteristics a part or material should meet, and the associated Qualified Product Listing lists those vendors and P/Ns that have been qualified by the standards group as meeting those standards.
Note that the FAA doesn't really acknowledge marketing data as acceptable.
Large air frame OEMs often have their own standards for same reason.
RTCA standards ensure compatibility systems that will interact with other systems or that must perform to a certain level so supporting groups can rely on their compatibility. Think ATC surveillance systems using data from ADS-B transponders to separate aircraft in IMC.

None of these are the words of a deity from the mountain that should receive dogmatic compliance. They just maintain safety in an unbelievably complicated and diverse industry.
 
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