I beleive a similar wiring installation was the cause of in-flight fire in a
Ban-bi in France. A small wire direct to the battery -ve had set fire to the
insulation causing a fire on the engine side of the firewall. I think the
wire also ran into the cockpit and caused smoke in the cabin.
Luckily the pilot was able to make a forced landing (maybe without flaps)
into a stubble field. Apart form the damage caused by the fire the A/C got
away unscathed. It is my understanding that separate -ve wires to the
battery are a bad idea for this very reason. The earth return should be
taken back to the non battery end of the earth strap (the engine).
In the case of the Ban-bi it was just ordinary electrical power and not the
starter that had caused a fire in a very undersized wire when the main
engine earth wire failed due to incorrect installation.
Hope this helps.
Jerry
Jerry@ban-bi.com or LTS@avnet.co.uk
www.Ban-bi.com or www.avnet.co.uk/touchdown
----- Original Message -----
From: "Alan D Stewart" <alan.stewart@blueyonder.co.uk>
Subject: Battery cable - corrosion
>
> I had an incident in my aircraft last weekend. The issue involved a
> battery cable and my lack of awareness of the real corrosive power of
> electrical potential.
>
> Paradoxically, headset noise was the first sign of trouble. A background
> drone shadowed the engine frequency in flight.
>
> In an effort to resolve the issue, I pulled the panel in a fruitless
> search for broken earth cables, wiring issues and suchlike. Thereafter,
> the engine was reluctant to start due to insufficient cranking power.
> 'What had I done ??'
>
> On my next starting attempt, the engine once again cranked reluctantly.
> This was immediately followed by the appearance of frightening amounts
> of smoke from behind the panel !
>
> A dramatic evacuation followed and the fire extinguisher was made ready.
> Fortunately, the smoke cleared in less than a minute.
>
> Cutting to the chase, this problem arose from corrosion.
> Specifically, corrosion on the inside face of a battery earth cable lug
> at the battery attachment point. (seems obvious with hindsight, doesn't
> it !!)
>
> On the negative battery terminal, I have:
>
> 1/ A large gauge, starter earth cable. (Oxidised, on closer inspection)
> 2/ A smaller gauge 'panel earth'. (Functioning normally).
>
> During cranking, because of significantly increased electrical
> resistance on starter earth, most of the negative charge was re-routed
> and bourn by 'panel earth'. Consequently, this melted insulation on thin
> earth wiring behind the panel, which was completely unable to bear the
> electrical load of the starter.
>
> Once repairs were completed, the headsets too, performed normally.
> Indeed it's worth noting that they were responsible for 'red flagging'
> the problem in the first place.
>
> Obviously, battery earth will now receive regular close attention and
> will be thoroughly corrosion protected. This is my lesson.
>
> Alan
>
>
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