Switches

[EricJ]

23 hours ago, ArtVandelay said:

I do not, I assume they’re stamped if I ever need to replace one of them.

Electric parts are standardized, don’t require TSO, mil spec, etc according to Mike Busch. I don’t remember the entire list, but I think some hoses, rivets, sheet metal screws are similar.

My avionics shop didn’t hesitate when I asked for regular mini rocker switches instead. They are a repair station so I think they’re well versed in what’s legal and what’s not.

The breakers are with all the others on copilot side.

This has been my understanding as well.   Electrical parts in particular don't have a lot of requirements since nearly everything is "standardized" to some degree.   There are charts in 43.13 for determining wire size for loads, etc., methodologies for load calculations and practices for proper sizing of fuses/breakers/switches/etc.    To my knowledge none of us are manufacturing airplanes, so the construction/manufacturing/engineering FARs don't apply, and 43.13 is not regulatory.

It has always been the case that landing lights and their respective circuits can be maintained/overhauled/redone by owners, and historically those were high-load, high-current circuits.   This seems to indicate that the FAA is not overly concerned about such things.   If fuses/breakers are properly located and sized and installed, as they should be per guidelines and reasonable common practice, the rest of it is pretty well fault protected.   In this case the switch may be the breaker, so it is definitely important to make sure that the proper circuit protection is maintained somewhere.

When my avionics were redone in my airplane I asked the shop to put in a couple cigar lighter outlets in the back seats and an additional one in the panel.    They got them off the shelf at autozone or someplace similar.    There are TSO'd outlets available for some outrageous price, and the TSO is for DC-DC converters, and the parts you get are the same ones you'd get anyway, so the TSO route is pretty comical sometimes.

[jaylw314]

On 4/20/2023 at 10:01 AM, N201MKTurbo said:

You say the manufacturer has a lot of latitude in specifying parts, yes they do, but they will need engineering approval for anything they specify. It seems that a DER/DAR analysis would be necessary and then a field approval. You can say these are minor alterations, but the rules say that minor alterations have to be done using approved methods (43-13.1B) and approved parts.

Just for future reference, minor alterations just require acceptable data (including the methods and standards in 43-13-1b), not approved data.  I don't know what that means for the parts specifically, though

[FlybyNite]

On 4/19/2023 at 11:47 AM, PT20J said:

Keep in mind that most of the Klixon and ETA rocker switches are actually circuit breakers, so if you replace them with just a switch you will have to add circuit breakers and do some rewiring. If you want to keep the circuit breaker function, your choices are more limited.

thanks, with the 930 cleaning up the old gauges, I'll have more room, plus I have a lot of old CB's from previous installed equipment that has been removed but the CB's were left in place. 

[Denis Mexted]

Alright. Back to switches. 

How are people complying with AC 43.13-1B ? Specifically the derating factor. 

So for a 12 VDC system, for a 10 amp light, a 50 amp switch is required. 

Looking at the Carling Technologies I don't see anything that amperage.

Am I missing something?

[ArtVandelay]

Alright. Back to switches. 
How are people complying with AC 43.13-1B ? Specifically the derating factor. 
So for a 12 VDC system, for a 10 amp light, a 50 amp switch is required. 
Looking at the Carling Technologies I don't see anything that amperage.
Am I missing something?

I don’t have any motors or incandescent lights, mine are all LEDs, 1.2 amps or less. Modern electronics all have voltage regulators (that’s why they work with 12v or 24v and why they can be on during engine start up and shutdown) and don’t have a start up draw either.
So my derating factor is 1.

[PT20J]

The reason for derating switches is that non-resistive loads frequently draw current when first energized (called inrush current) that is greater (sometimes much greater) than their operating current. Switching power supplies, depending on design, can be troublesome. I found this out when designing a piece of telco central office equipment years ago. No one bothered to tell me that a requirement was that the power supply had to be hot swappable and I didn't specify low inrush current to the power supply vendor. Every time we tried to hot swap it, it fried the connector and we ended up having to redesign the power supply.

Incandescent bulbs have high inrush current because for a few milliseconds until the filament heats up they have very low resistance. The derating table 11-4 in 43.13-1B calls for derating a 12V switch for a lamp by a factor of 5. This is not unreasonable for long switch life and I have seen that or similar deratings elsewhere. But, as pointed out, it requires a pretty hefty switch for a  landing light. I'm not sure what is common practice by airframe manufacturers. It would be interesting to look up switches used by other manufacturers (that don't use circuit breaker switches) to see what common practice might be.  The tradeoff with lower derating might be that the switch would have a shorter service life. But as switches are generally rated for tens of thousands of cycles, and landing lights are used less frequently, perhaps this is a reasonable design tradeoff.

[PT20J]

Perhaps my suggestion to reference what airframe manufacturers use is not such a good idea. It occurred to me that Cessna uses little 15A rocker switches. Some searching turned this up. Note that the switches are rated for 100,000 cycles, but Cessna’s application for incandescent lamps seems to kill them after about 4,000 cycles.

[Denis Mexted]

Thanks for the education guys. 

I replaced all the breakers in my C180 when I did a number on it, but not the switches. Reading the above, maybe I should have done both.