circuit Breakers

dacker · Post by **dacker** » Fri Nov 21, 2003 12:58 am

I am in the process of rewiring my 49 A model and decided to replace the fuses with Klixon CBs. I could only barely read the markings for the fuses but it looked like all (not counting the alternator) were 10 amps except for the landing lights which I read to be 25 amps. This seems a bit high to me, but that was what was in the fuse holder. Before I open the packages that the fuses came in can someone confirm what these circuits are rated at?
Thanks
David

(Especially since that little 25 amp beauty was around $60!)

Dave Clark · Post by **Dave Clark** » Fri Nov 21, 2003 1:45 pm

It's shown in the early 100 Series Service Manual But.... how do you know if the wiring is currently as original? Now would be a good time to have a knowlegable mechanic at least inspect your wiring for condition and design. He could easily then tell you the circuit breaker size for your system. Messing with the wiring on a 50 year old airplane can get you in a lot of trouble, and someone has probably been there before you. Chances are good at least one thing isn't right so don't just take the easy way and replace the breakers.

dacker · Post by **dacker** » Fri Nov 21, 2003 2:41 pm

Like I said I am rewiring my 49. I have just replaced the left wing and all of its associated wiring, I am not just replacing fuses. You are right about someone already being there before me, I have pulled out all sorts of crap including automotive wiring and a ton of those nifty little twist connectors like you use in your house. I am trying to ascertain what the markings are on the panel above its associated fuse. Mine have been painted over and it is hard to read. I don't have the early 100 series service manual - yet.
David

mit · Post by **mit** » Fri Nov 21, 2003 3:15 pm

look in the parts book

dacker · Post by **dacker** » Fri Nov 21, 2003 5:47 pm

OK, the parts book was the first place that I looked. Unless I missed it, I didn't see any reference to amp loads on the circuit diagram in that publication.
If I calculate the amp draw of two 100 W landing/taxi lights I come up with a little less than 17 amps. Maybe a 25 amp fuse isn't so large after all. But I am simply asking what are the markings scribed on the panel just above the fuses. Mine have been painted over so that this particular one is unreadable. It looked like it read 25 amps, the old fuse that I pulled was 25 amps, there is nothing else on this circuit, so it is safe to bet that the stock markings are correct. My mechanic has my parts manual so I don't have it in front of me to search through it again right now.
David

doug8082a · Post by **doug8082a** » Sat Nov 22, 2003 5:12 am

The best place I've found for this is an ORIGINAL owner's manual rather than the IPC as it has a very good picture. I have a '52 which shares the same panel configuration as in your '49 and was the last year for that design. According to my '52 owner's manual, the fuse markings on the panel are (from Left to Right) as follows:

Gen - 15 Amps
Radio - 15 Amps
Nav Lts - 10 Amps
Panel Lights/Heater - 15 Amps
Lndg Dome Lts Dimmer - 25 Amps

These markings also match a '50 A panel I have in my basement that I'm using for my panel restoration.

Good luck,

mit · Post by **mit** » Sat Nov 22, 2003 9:55 am

dacker wrote:OK, the parts book was the first place that I looked. Unless I missed it, I didn't see any reference to amp loads on the circuit diagram in that publication.
If I calculate the amp draw of two 100 W landing/taxi lights I come up with a little less than 17 amps. Maybe a 25 amp fuse isn't so large after all. But I am simply asking what are the markings scribed on the panel just above the fuses. Mine have been painted over so that this particular one is unreadable. It looked like it read 25 amps, the old fuse that I pulled was 25 amps, there is nothing else on this circuit, so it is safe to bet that the stock markings are correct. My mechanic has my parts manual so I don't have it in front of me to search through it again right now.
David

Figure35

Item 52-55 verify your wireing before you select your fuse/breaker size.

dacker · Post by **dacker** » Sat Nov 22, 2003 5:25 pm

Thanks Doug, the Radio CB and Panel Lights/Heater CB may be different, I will need to confirm the Radio load. I don't have a heater wired to my panel lights, so 10 amps is plenty for that circuit. I have a Jasco alternator that some one else had installed with a 50 amp CB, I don't need to mess with that as it appears to have been done correctly and neatly and I have never had any problems. Tim, I appreciate what you are telling me as far as verifying the wiring; I have, it is mostly crap. If you are talking about verifying the wiring and applying the appropriate CB per AC 43.13 so that the CB pops before the wire burns, that want be a problem. Since weight isn't an issue I am not trying to use the smallest wire that I can get by with, in some cases the wire will actually exceed what was stock.
I appreciate everyone's information as this is another learning experience for me!
Hopefully I will have a nice little trouble free A model for years to come after I finally finish.
David

Post by **GAHorn** » Sat Nov 22, 2003 9:54 pm

David, keep in mind that CB's/fuses DON't protect the appliance. They protect the wiring. So the CB/fuse should be sized in accordance with the wire gauge and type. I listed these in a chart on another post last year and it can be found with a search routine. Your elect. diagrams will specify the wire size, and also the fuse size for that circuit.
Example: Your alternator was upgraded to a 50AMp unit. So the installation increased the size of the Fuse/CB for that item....but NOT because the alternator was of higher capacity. It was done because the actual wire servicing that circuit was also changed ot a larger gauge. (or at least it SHOULD have been!) Again, the CB does not protect the appliance. It protects the wire.

dacker · Post by **dacker** » Sun Nov 23, 2003 1:22 am

George, that was what I was trying to say; in AC43.13 there is a chart that basically gives the correct (read max amp rating) of the CB per the guage of wire. What this means to me is that the CB will trip before the wire burns/melts. I believe that I will be safe/correct enough on those circuits that were factory installed. For instance, my panel lights, are pretty straight forward, say using 14guage wire (I believe the chart gives a max amp rating of 20 but I don't have it in front of me) then I can't go wrong with a 10 amp CB. But regardless, I think I will sit down with one of the mechanics that are helping me with my airplane and solidify my plans before proceeding any further. I think this horse has been ridden about as far as she can go.
Thanks to all!
David