Hi,
I have an unsolved problem with the main circuit breaker panel of my Silver Eagle. May be someone has an idea...
If the outside air temperature is high (> 30° C), the breaker panel located on the left pilot's side is getting quite hot and circuit breakers start popping out. Sometimes 3, sometimes 4 breakers are out and I'm not able to push it in again because the panel is too hot and the fuses always pop out again. I had this recently that the prop de-ice fuse was out and I was in an IMC climb.
My avionics shop opened the fuse panel, pic of the opened panel see below. You can see that the isolation of one of the 2 thicker cables already melted due to the heat.
Everything works under normal OAT. Any ideas? Thanks.
Some very quick first thoughts:
-) a single photograph isn't much to go by, however well lit and angled, so any comments must reserve a wide margin
-) it seems not a problem of ventilation: if it were, the next thickest cable would be affected too. Or is it, but hidden behind a veil of heat shrink shroud?
-) seeing this one photo, I distrust the overheated cable. Looks like having been soldered upon, ans also brutally plied just beyond the mount point (inside joke for Unix guru's...)
-) in a temper of general whining, I quite dislike the floating fuse holders - there may be situations where one makes a fair compromise, but four of them is simply too much
-) is this a certified plane? If it is, the owner might well consider a critical discussion with however was last in charge of this electrical installation. If not, I dare recommend a redo, partial or full
-) strange to see crimp-on terminals in red (for the smallest wire gauges) and yellow (for the largest) but not a single blue one (which is most common, serving 2,5 mm2 wire, quite a common requirement)
That looks like a really badly made crimp joint, which is getting hot.
I had exactly that with a 6kW heater (non aviation) and it melted the wire insulation.
I suggest re-making that connection, by starting with a new terminal and soldering it (not crimping it) thoroughly. It should be well flooded with solder.
My guess is that the bad joint (and maybe there are others also that are loose; I see other crimps) is heating up the whole panel, with the heat being conducted via the thick aluminium bus, and pushing the CBs near to their trip currents. They are only thermal after all, i.e. pretty crude and ambient temperature dependent.
There is some very untidy wiring down there, with those horrid inline fuseholders, also made in what looks like PVC wire (the red and black). One should use only high temperature cable on aircraft.
Peter, glad to agree with you about the floating fuse holders. However, regarding your quote "One should use only high temperature cable on aircraft" I think it depends on the importance of electrical power. On low-profile planes, like Piper Cubs or Moranes or perhaps even C152. C172, PA28 &c, flown only in strict VMC, a total loss of electrical power should not be dramatic. Given a very correct scheme of wiring and fusing, such a plane should be able to make it, in acceptable safety, to the next aerodrome; even if all fuses burn out. But the fuses/breakers should and must then trip at need, so the electrical installation must have been well thought over, however simple it may be.
For high-profile planes like yours, I agree one cannot go too safe, so the extra cost of PTFE insulation seems quite justified.
The "aviation grade" wire isn't PTFE; it is some sort of cross-linked ETFE. See Raychem 55. PTFE is much more expensive than Type 55.
The problem with PVC wire is that its temperature range doesn't give you much leeway when it comes to a possible ambient temperature, or a wire bundle temperature where wiring is in a confined space. It's also soft and vulnerable to mechanical damage. In the photo above you have wires passing over metal terminals, etc, under vibration conditions.
I wouldn't fly any plane built to that standard; an in-flight fire on a Piper Cub is going to be every bit as much fun as on a TB20 
Thanks for your quick answers.
The panel is from the 1998 turbine conversion so it's original O&N installation. I asked them about this (send this very same picture). They told me to check the current draw on the thick lines. My maintenance shop did it and it was 7 resp 10 amp with air conditioner on (they were suspection the a/c). So it actually can't be an overload.
I showed it to Avionik Straubing and they were not sure whether the melting was an incident that was already fixed. However, they recommended to replace the whole panel. I like to do that but they are full until March 2014. So I'm now looking for a decent avionic shop. Any suggestions? Germany and around is fine. Should not take longer than 1 overnight stay.
Do you know the function of each of the thick wires?
The recommendation to replace the whole bung sounds like too easy money for the recommender. If you take such an offer, you should at least require a guarantee that the present issue will be solved. And that seems quite questionable, again seeing from this one photo.
And, err, excuse me to repeat the question: is this a certified plane/installation?
What means certified? It is a N-reg turbine conversion and I guess the electrical system is part of the STC. So, yes it is.
I'm not sure what is more expensive. Letting them search for the reason or just to replace the panel. One problem is that it takes some time until it gets warm and I don't know whether I need to have the turbine running (generator) or not.
I don't know what the thick cables are for. Seems to be the main power lines. There is 150 amp breaker to avoid a generator overload, too. That breaker doesn't sit in the panel but underneath the avionics panel.
I can see why they might want to rewire the whole panel...
I would re-do the whole thing too.
Aircraft CBs are not the best quality products and do degrade over time; I think because they run pretty warm all the time anyway.
Without having the knowledge Peter has I would say that this is such a sensitive area that I would not spare any expense to get this done perfectly. You do not want to fly a turbine aircraft with such a problem. This will probably cost you some money, but THIS is really worth it, I think
