Author Topic: Oxidised wiring caught fire  (Read 5684 times)
imj
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Oxidised wiring caught fire « on: March 09, 2013, 06:41:58 AM » Author: imj
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Medved
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Re: Oxidised wiring caught fire « Reply #1 on: March 09, 2013, 07:34:03 AM » Author: Medved
The soldering there didn't help there either, if it was not even the cause - the mix of metals create galvanic cells, the PVC residues actas an aggressive electrolyte,...
Moreover the tin/copper interface layer is very weak and fragile, so it could crack even by slight mechanical stress (movements when you insert/remove the plug, heating up,...), then create voltage drop, heat up, decompose the PVC to the aggressive chemicals and you could be there...
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Re: Oxidised wiring caught fire « Reply #2 on: March 09, 2013, 08:09:08 AM » Author: imj
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Medved
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Re: Oxidised wiring caught fire « Reply #3 on: March 09, 2013, 09:34:22 AM » Author: Medved
Some additives in the PVC tend to be very corrosive towards metals.
And the PVC itself, when exposed to heat, releases the chlorine, so again quite corrosive material.
And it may happen, then some fault during the PVC manufacture may cause the components to not react properly, again causing very corrosive environment (chlorine compounds,...)

I've seen such PVC cables, as well as the presumably silicon cables corroding very heavily. And some other batches from the same product were just fine...
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Re: Oxidised wiring caught fire « Reply #4 on: March 09, 2013, 10:52:33 AM » Author: imj
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Re: Oxidised wiring caught fire « Reply #5 on: March 17, 2013, 11:07:21 AM » Author: imj
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Re: Oxidised wiring caught fire « Reply #6 on: March 17, 2013, 12:37:17 PM » Author: Medved
If it was aluminum involved, I think the soldering was a huge contributor to the problems: The flux is aggressive, the heat from the soldering caused the ends to oxidize and at the same time released another aggressive compounds from the plastic.

But for fixed installations the best is to avoid stranded conductors and use only solid core. It is about half the cost and way more robust. Even when aluminum, it's relatively small surface area (compare to stranded cables) make it last at least for two decades, if properly installed, even when the materials (plastics, aluminum purity,...) are not the best ones.

Of course, the best is to use solid copper (and if I remember well, it is the only material allowed for home installations made here today; at least it is the only used), even with quite bad plastic the installation use to last for decades...
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Re: Oxidised wiring caught fire « Reply #7 on: March 17, 2013, 04:49:03 PM » Author: imj
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Re: Oxidised wiring caught fire « Reply #8 on: March 18, 2013, 01:04:10 AM » Author: Medved
And where do you are from?
Here only the solid core copper is available in the form of cables for the fixed installation and no one sane ever use anything else...

One of the main reason behind is the failure mode: The solid core wire is either complete, so conduct the electricity without any extra losses, or broken, so does not conduct at all, so again no power dissipation. So the only places, where it may heat up are the connection points (junction boxes, outlets,...), but those are limited places and so are possible to cover by inspections.

With stranded cables, if the strands oxidize and few of them broke, the current flow only through limited cross-section, but it still remain somehow conductive. So nothing prevent the operation with an overheating cable...
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Re: Oxidised wiring caught fire « Reply #9 on: March 18, 2013, 01:33:43 AM » Author: imj
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Re: Oxidised wiring caught fire « Reply #10 on: March 19, 2013, 01:42:31 AM » Author: Medved
And how the trunking look like? Here thesolid core wires are used inside channels without any problems - if you want to insert the cable, you remove the lid, insert the cable, around corners bend them to the required shape just before insertion, insert in this way all cabes you want toinsert and closethe lid again, so no problem...

And I checked by my colegues, who are more familiar with the code and they confirmed, than stranded wire cables are still not allowed in permanent installations (so allowed only in movable supply cords). And the reason are the dangerous, but not easy to notice failure modes of the stranded wires, mainly at higher loads.
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Re: Oxidised wiring caught fire « Reply #11 on: March 19, 2013, 02:11:24 AM » Author: imj
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Re: Oxidised wiring caught fire « Reply #12 on: March 19, 2013, 04:23:22 AM » Author: Medved
It's those two piece PVC trunking.

If it is the typeyou have on your video, this was never a problem with the solid core cables: Remove the lid, so you get a kind of groove from the plastic trunking, so you just insert the cable in.
And if I compare the power cables with rather soft IT cabling, the hard cables are for me easier to handle, because they moreless hold the shape, so if you make some bends, they stay in the groove even witout the cover, so you could prepare (form, bend,...) other cables to be inserted into the same groove while keeping the lid open...
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Re: Oxidised wiring caught fire « Reply #13 on: March 19, 2013, 11:08:31 AM » Author: imj
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Re: Oxidised wiring caught fire « Reply #14 on: March 19, 2013, 03:22:51 PM » Author: Medved
Well it's not that I'm against solid core wiring but there ain't any..:( So I resort to soldering the wires which is the closest thing to solid core at the termination point.

So then better keep the wires like they are, the soldering make the thing only worse - intermetallic compounds tend to be extremely fragile and the solder just "leak" between the strands, so you think you tighten it up, but after few days it become loose again...
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