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mkennard

Missed an earth cable

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Almost embarrassing writing this but I hope nobody else does it.

 

I took the battery home to give it a good charge and put it back in on Saturday, I missed one cable, probably a critical cable, the earth for the starter.

 

I could see the starter light stuck on and there prop didn't turn. Smoke started pouring out of the engine bay and of course all the switches I flicked off. No change, still heaps of smoke. I grabbed the fire extinguisher and thought I crossed a wire so my first aim was to disconnect the battery.

 

Succeeded in disconnecting the earth cables. What a mess. After talking to my mechanic, he has seen this happen before, the positive somehow jumps, not sure how and it looks like it used the throttle cable as the earth. The throttle sheath melted and the metal also melted the side of the battery.

 

A solution is to cable tie the cables so none of them can't drop out of sight. Been flying for 9 years and haven't done anything like this before.

 

Please take note.

 

 

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What happened is that closing the solenoid connected the battery 12 volts to the starter and therefore to the engine block. The throttle sheath connected the engine block to the firewall earth.

 

Well you found out that the cable and sheath got real hot with the resulting current.

 

Thanks for telling us, this is how it is supposed to work, but these days some people are getting reticent for fear of repercussions.

 

There was a Jabiru at Bundaberg which was burnt because of some electrical fire which started in the air and I don't know the reason for that one.

 

 

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I did this in a Datsun Sunny once, it welded the inner to the outer of the accelerator cable in the process.

 

 

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Bruce , the one in bundy you mentioned was a j200 or 230 19 xxxx

 

I spoken to the crew who picked up what was left , in a bucket !

 

Another poor wiring job in a home built , ( not saying any thing about the sonex , )

 

 

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Yes the throttle cable takes the lot or some small oil pressure pipe. It is a good idea to run 2 earth cables engine to frame they are short and don't add much weight. Nev

 

 

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Yes the throttle cable takes the lot or some small oil pressure pipe. It is a good idea to run 2 earth cables engine to frame they are short and don't add much weight. Nev

Yep. I think that's on my list.

 

 

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Yep ... the lesson is, if you don't know what you are doing or the consequences, don't do it. If you are disconnecting something you are not sure of, tie and label all the cables and document where they go BEFORE disconnecting. There is a lot to this electrickery stuff.

 

 

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good on u tho mkennard im still only new to flying training and not interested in building my own aircraft.however i may still do certain amounts of maintenance and knowing what u have described only helps me and others to benefit in the future.thanks for having the guts to share it.

 

 

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I've taken to doing something that some others may find helpful.

 

These days there are so many connections to some devices that I have become a bit fearful of getting the wrong wire on the wrong terminal. Recently I bought a second-hand intercom system that has all sorts of clever interfaces for phone, flight radio, music, annunciator system and so on. Unlike the old simple intercoms with power and a couple of mono-jack inputs, this thing has more than a dozen identical spade terminals on the back plus a couple of interchangeable multi-pin plugs and a few others to boot.

 

The thing came with a wiring loom attached but naturally it wouldn't fit my installation so I needed to pull the loom apart and re-make it. To do that I would have to disconnect all the terminals and plugs and it didn't come with a manual ...

 

Initially I drew a large diagram and started labelling all the terminals and wire colours on it, then had my 'bright idea'. It's so obvious I don't know why I didn't think of it before, and given that we all have mobile phones with cameras ... I just took a few photos of it.

 

Now I do that with anything and everything I'm about to work on and I find it very re-assuring to check the photo(s) against the re-assembled item before hitting the 'go' button.

 

Maybe I'm just getting older and the memory's not quite what it used to be, but it works for me.

 

 

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Sorry David, I understand what you're saying but this was a mistake. Now your saying don't touch what you don't know, strange, I've picked up mistakes from LAME's and Level 2's. That's why I always check what has been done after a service before I fly. What I did was a pure mistake and can happen.

 

As for "Head in the Clouds", I don't think age has to do with that, photos are a wonderful way of auditing the process and getting it back together again.

 

 

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I agree mkennard, we all make mistakes however careful we are.

 

I'd just like to commend you for posting here about this, it's easier to just keep quiet when we trip up and save the embarrassment but by bringing this to our attention you will quite likely save others from making similar mistakes and the outcome could be much worse than it was for you. I certainly hadn't considered the consequences of not connecting the starter earth cable, the natural assumption would be that it just wouldn't crank, not that a disconnected cable might cause a fire ...

 

Thank you.

 

 

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Well the problem is there are other pathways and they are not designed to carry the current.mkennard you have done exactly the correct thing, by your candidness. Any one who hasn't made a mistake hasn't made anything..

 

With a high amperage circuit like the starter, if there is any sluggishness, have the cowl off and run your hands around checking for any heated items (carefully). ALL connections cables and wires, starter solenoid etc. Any poor connection will identify itself. With a missing connection such as you had may result in very rapid heating of cables and solid oil lines as to some oil pressure gauges. You best indicator there is the starter will be sluggish but the damage will be done in seconds. Nev

 

 

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Sorry David, I understand what you're saying but this was a mistake. Now your saying don't touch what you don't know, strange, I've picked up mistakes from LAME's and Level 2's. That's why I always check what has been done after a service before I fly. What I did was a pure mistake and can happen.

As for "Head in the Clouds", I don't think age has to do with that, photos are a wonderful way of auditing the process and getting it back together again.

wasn't meant to criticise you buddy. Just a comment for those who dont know. Yes we all make mistakes HITC idea is great; I recently awoke to the use of my iPhone for that very purpose ... all the details in your pocket.

 

 

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Also with the picture in your phone it is so much easier to share, I use them when ordering spare parts or something tricky just take a pic and send it direct to the people who know:thumb up:. It saves a lot of hassle getting model numbers ect.

 

 

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When I visited the NASM restoration facility at Silver Hill in 1991 (I think it was), I discovered that they took videos and pictures of all important dismantling (VHS tapes, in those days) and used them extensively when re-constructing the aircraft - sometimes years after the dismantling - and by a team that had changed volunteer members many times. The TV, picture files and vhs tapes were a significant part of the 'reconstruction' area that was set up around the aircraft when it came time to put everything back together, and they had special (large!) trolley arrangements with all the pictorial and written stuff that would be wheeled into place.

 

It was a brilliant concept; before any major job started, the restoration team would sit down and review all the relevant videos etc and discuss the work schedule. The NASM team had become quite expert at taking videos with great detail, so they could 'reverse-engineer' the strip-down sequence and not find themselves having fastened something in place that meant something else could not easily be re-attached etc.

 

 

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Pulling things apart requires little skill especially if done carelessly. Poor dismantling and storage does a lot of damage to things. So much better result if you document everything. Nev

 

 

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I made the mistake of photoing the avocet build , plugs , layups ect , but LOST it all , not backed up . Now i use the i clould for back up , got the rebuild though !

 

I still shead a tear if i think about it to much !

 

Mike.

 

 

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