The International Cessna 170 Association

Hi ... Levi you did what I am now doing. I too have found wires that seem to go nowhere from previous installations and am running those down. I am going to replace the Klixon thermostat with a CB(s) as required. I have hand drawn several electrical "maps." I drew up a list of installed equipment and am running down the needed CB/wire size which is the current (pardon the pun) challenge. The main issue is the size of the wires to be used. Example: I am installing Whelen Orion NAV/ACL (anti-collision. i.e. strobe) lights in the wings and tail ... Whelen calls for 20 ga wire ... 18 may be better in "light" of the length of wire needed. The current strobe will become a low-intensity beacon and I am going all LED for interior /instrument lights. A radio/avionics bus is going in as well. If you do not mind, I would like to see a copy of the diagram you mentioned. Should I send you my usual email? (I do not want to violate Forum rules and protocol!) I appreciate the help! The work is interesting and should result in a safer airplane. Thanks ... R/Lee (N1967C)

PS I am using AC 43.13 and ASAs Aviation Mechanic Handbook for quick reference ... good info

Allow me to play big-shot for a moment and suggest/remind you that subsequent owners and repairmen who work on your airplane will greatly appreciate your clearly and accurately documenting in the permanent maintenance records the modifications (even minor ones) which you accomplish in this work.

Nothing would be more frustrating to a future owner/mech. than to rely upon factory documentation while working on a modified airplane with no obvious record of the mods. A photocopy of the appropriate page from the IPC which clearly demonstrates the changes from original equipment or design... and kept with other Form 337s, STCs, etc. in/on the airplane records will go a long way to keeping your airplane airworthy.

It took me a while to figure out that I can't attach images, so here is a link to the PNG version on my Google Drive:
https://drive.google.com/file/d/1v4mFH1 ... sp=sharing
Hope it gives you some ideas. I like the idea of doing all LED panel lights. I'd love to see how you do that because I want to do something similar, I just haven't figured out what yet.

Arcticmayhem wrote:It took me a while to figure out that I can't attach images

Levi, I've fixed your forum privileges. You now have member privileges including the ability to attach pictures.

Here is the image you linked to in your Google Drive.

Thanks for the diagram ... interesting ... useful info ... much appreciated. I will pass the word once I figure out how I am going to do the LED interior lights. By the way, this morning I was reading AC 43-13B this morning and found an interesting comment on page 11-15, para 11-50 (b) ... “Automatic reset circuit breakers, that automatically reset themselves periodically, are not recommended as circuit protection devices for aircraft.” I may be missing something but, this sounds like the 2 amp thermostat/current limiter (Klixon) I found behind my instrument panel ... thoughts? R/ Lee (N196C)

Oooops ... my N number is N1967C ... apologies for the typo. R/ Lee

Lee wrote:Thanks for the diagram ... interesting ... useful info ... much appreciated. I will pass the word once I figure out how I am going to do the LED interior lights. By the way, this morning I was reading AC 43-13B this morning and found an interesting comment on page 11-15, para 11-50 (b) ... “Automatic reset circuit breakers, that automatically reset themselves periodically, are not recommended as circuit protection devices for aircraft.” I may be missing something but, this sounds like the 2 amp thermostat/current limiter (Klixon) I found behind my instrument panel ... thoughts? R/ Lee (N196C)

43-13B is acceptable methods not absolute requirement. The mfr'r (Cessna) had their reasons and their design is approved.

It is true however that modern philosophy on resetting C.B.'s is.... if it's not absolutely necessary to have that item to complete the flight....DO NOT reset a circuit breaker or fuse. The old idea of resetting it "once" is ok.... is out the window.

I agree George ... “wires and fires” are to be taken seriously. In my previous life, we could reset a breaker (other than fuel boost pump) if in flight and the item was needed. If in deck, we had to contact maintenance and let them deal with it. Interesting that Cessna had the auto reset current limiter/breaker ... I may be missing something but it sounds to me like the current limiter/breaker/thermostat could trip if too hot, cool down and then re-set automatically ... and we have no control over its functions? This is another reason I wanted push-pull breakers instead of pop-out breaker and/or fuses as was the case with my airplane. If things are going awry electrically, I want to be able to positively remove power.

Here is something that struck me as well: I talked to Whelen yesterday regarding the size of breakers to use for their Orion LED Nav/Strobe lights. They recommended 16 or 18 ga wire and a 15 amp breaker for three Nav lights and a 15 amp breaker for three strobe lights. Oddly, the lNding and taxi lights, also Whelen LEDs, combined, are 5 amps ... recommended. Given how little the LEDs draw, the impression I have is that the higher ratings for the Nav and strobes are due to the length of the wires. Any thoughts?

Also ... what does a heated pitot draw? I can’t find a reference ... also appears the stall warning actuator is heated? Thoughts, comments appreciated! Regards, Lee

Lee wrote:I agree George ... “wires and fires” are to be taken seriously. In my previous life, we could reset a breaker (other than fuel boost pump) if in flight and the item was needed. If in deck, we had to contact maintenance and let them deal with it. Interesting that Cessna had the auto reset current limiter/breaker ... I may be missing something but it sounds to me like the current limiter/breaker/thermostat could trip if too hot, cool down and then re-set automatically ... and we have no control over its functions? This is another reason I wanted push-pull breakers instead of pop-out breaker and/or fuses as was the case with my airplane. If things are going awry electrically, I want to be able to positively remove power.

Here is something that struck me as well: I talked to Whelen yesterday regarding the size of breakers to use for their Orion LED Nav/Strobe lights. They recommended 16 or 18 ga wire and a 15 amp breaker for three Nav lights and a 15 amp breaker for three strobe lights. Oddly, the lNding and taxi lights, also Whelen LEDs, combined, are 5 amps ... recommended. Given how little the LEDs draw, the impression I have is that the higher ratings for the Nav and strobes are due to the length of the wires. Any thoughts?

Also ... what does a heated pitot draw? I can’t find a reference ... also appears the stall warning actuator is heated? Thoughts, comments appreciated! Regards, Lee

Well, I am surprised at the recommendations made to you by Whelen. The 18 or 16 ga. wire is protected by Cessna with a 10A fuse. ...and as we've already noted... the circuit limiter used protects the WIRE....not the appliance.
As for the landing lights, the original circuit protection for the incandescent GE4509 lamps included a cigar lighter which subsequently was the subject of an AD note which requires separated protection. (Cessna protected the land/taxi/lighter circuit with a 25A fuse.) Each 4509 draws 100 watts (7-8Amps) and so a dual lamp install should have a 20A fuse/C.B. serving minimum14 ga wiring.

(Note: those who reference the table in the Electrical Service Manual should note that the amp ratings for various wire gages are for continuous loads in bundles. Individual wires which are intermittent loads may be allowed higher ratings, and that is what Cessna engineered. An extreme example of Cessna's use of intermittent/individual wiring ratings is the battery/starter circuit where 4 ga wire is expected to carry up to 600 amps for short periods.)

Greetings ... Re: Whelen Orion LED Nav/ACL (anti-collision/strobe) lights: just talked with another tech rep at Whelen and he told me that a 1 or 2 amp CB for all three Nav lights would be proper with the current wiring. For the ACLs, a 10 amp CB with 16 ga wire (preferred, 18 ga acceptable) would be sufficient. This sounds better than the original figures I was given on Tuesday. R/Lee (N1967C)