Lotus Elan

Fire risk with Thin Wall versus standard PVC cable?

PostPost by: oldchieft » Mon Jul 27, 2015 8:51 pm

Good day all.

I hope someone can update my knowledge.

Up till now i have used the PVC covered wire the we all grew up with.

This is now hard to get and often the tracer colour is just painted on.

I have moved on to thin wall wire for the job I am now working on.

This claims a higher current rating then the old stuff.

The insulation is rated at 105 degrees C, the old stuff 70 degrees C.

The old 28 strand 0.3 cable is rated at 17 Amps, the same in thin wall at 25 Amps.

Am I correct in thinking the only thing that has changed is the wiring is allowed to run hotter?

This would be OK if the whole system is changed, but could be a very fine fire lighter if mixed with the old stuff?

In fact this may have been the start of otherwise un-explained fires.

Can some expert on this tell me if I am correct?

Jon the Chief
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PostPost by: Chancer » Mon Jul 27, 2015 8:57 pm

More likely that it runs cooler because it has less thermal insulation so can therefore carry a higher current without overheating.

Probably academic when its bound in a loom with all the other cables.

The fuse will have blown a long time before the cable reaches 70 or 100?c

For unfused circuits like the ignition and charging systems its only short circuits that you need be concerned with, in that instance both types of cables would glow red and melt all the insulation.
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PostPost by: bill308 » Mon Jul 27, 2015 11:27 pm

Assuming wire size and conductor material (specifically the purity of copper) and PVC mix is the same, thinner insulation means lower conductor temperatures. Because conductors have some resistance, heat is generated when an electrical current is flowing. The insulation acts as a thermal resistance, reducing heat transfer to the local air.

Quality wire often has 2-temperature limits cited, a higher one when operating by itself, in air, and a lower one when bundled with other cables as in a loom.

Aerospace devices use Teflon coated insulation for higher heat resistance and abrasion resistance.

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PostPost by: StressCraxx » Tue Jul 28, 2015 1:37 am

bill308 wrote:
Aerospace devices use Teflon coated insulation for higher heat resistance and abrasion resistance.

Bill


Bill,

Are you talking about Tefzel coated wire?

Regards,
Dan
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PostPost by: gus » Tue Jul 28, 2015 11:27 am

Teflon insulated wire is standard in high end electronics.

I have used it in my cars for years, as it is completely oil proof and completely heat resistant[heat from headers will not melt it]

It is not as abrasion resistant so you need to be more careful in some cases.
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PostPost by: oldchieft » Tue Jul 28, 2015 9:37 pm

I got a reply back from Autosparks that sheds some light on the issue.

Quote
Hi Jon

Thank you for your enquiry, to advise yes, it allows the cable to run hotter, but it?s also thinner, as you can appreciate as car electrics became more complicated they need to change the style of cable, otherwise tree trunks would be running through the cars!

Should be fine to mix and use both styles, just make sure you use the correct amperage.

Regards

Paul

Autosparks Ltd
80-88 Derby Road
Sandiacre
Nottingham
NG10 5HU
http://www.autosparks.co.uk
Tel: +44 (0)115 949 7211
Un-quote.

I would take this onboard when I chose wires, I think I would go for the same cross section as the old system when I am mixing with other wires,

Also in the back of my mind is the rating need to be reduced if cables are grouped.

The suff the hangs around in your mind for forty years or more is amazing!

I found a cable maker pdf that confirms this.

Cables in group/Rating factor
2 / 0.80
3 / 0.70
4 / 0.65
5 / 0.60
6 / 0.56
7 / 0.53
8 / 0.50

Probably of no use, just use the next size up or double it for extra safety.

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PostPost by: bill308 » Thu Jul 30, 2015 1:01 am

Hi Dan.

I'm not familiar with Tefzel wire. A trade name? Even Teflon, is a trade name.

Bill
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