Charred Earth Wiring

[Colin_374358138]

Hi,

Upon inspection of my cars 12s sockect I saw melting of the plastic on the centre pin.

This is presumably caused by high current flow. Any idea why the current should have been so high ?

I replaced the socket and the plug on the caravan too. Fine.

However when I re wired the new socket for the car I found that the centre black earth wire was black inside.

I stripped it back bit by bit to try and find a 'copper' colour centre. After stripping back the two inches that were slack, having no more cable to strip I had to stop and wire it in as it was. It was still black inside however.

I can't help thinking that this is a bad thing. Surely this wire will now have higher resistance and so get hotter. Plus it will make a less satisfactory contact to the pin its wired to.

Should I replace my 12s cable ? if so is this an easy job ?

Regards,

Colin

 

[Rod_5041370]

Cure it for good.

Change the plug, socket and cables for 13 pin ISO.

 

[Colin_374358138]

Not sure I want to go to the trouble and expense of that. I was envisaging a couple of metres of 7 core cable - job done for less than a fiver.

Also I have a truma mover which requires a 12n to be plugged into a an exta socket on the A frame as a safety measure - to stop it being operated by accident. With a 13pin I wouldn't be a able to do that.

I intend to join pin 7 and 5 (brown) inside the 12s plug and use the brown as an extra earth. I may also join 6 and 2 (blue) to use the blue as an extra supply.

I'll open up the back panel in the car to see how much hassle changing the cable would be.

My fridge has always been poor on battery and I think its due to lack of supply of leccy. I intend to improve the supply.

 

[JTQ]

Colin,

This is a common problem. I will give you my take on it as I had it and cured it.

A major reason for it is that the centre pin becomes "pinched in" making for a poor contact carrying the heavy current.

Its the high resistance of that poor connection that's the source of the heating, rather than the inadequacy of the wire.

The centre pin guides the two parts together and any "wiggling" to get the plug in and out pinches in the pin. You will find that if you try to "spread" the slots in the pin it will very likely snap one quadrant off as the brass has been denatured.

Only solution is to replace the plug then each time you make and unmake it do so without a hint of wiggling them.

I have had no repeat problems now for some years after realising this; hope it helps you. Cheers John

 

[Colin_374358138]

I think thats actually top advice. I can see where you're comming from.

Good point.

 

[WatsonJohnG]

http://www.towitall.co.uk/faq/faq1.htm
Its the load on the earth return to the fridge plus as has been said compression of the centre pin

Read this link

It worked for me

 

[ProfJohnL]

Hello Colin,

Clearly from your posting you are aware of the effect that resistance has on current flow and the resulting heating effect.

I am fairly sure that the other respondents have described one very probable failure mode where the bifurcated pin becomes damaged. The result of the damage is to increase the resistance of the contact, and by virtue of Watts = Volts x Amps, the contact will heat up.

So its not so much that an excessive current flowed, but more likely the current was quite normal but the resistance has increased.

A chain reaction sets up, the heat in the contact is conducted to the copper in the wires, the copper starts to denature and to melt the cable insulation. The chemicals from the insulation become mobile and become deposited on the individual strands of the copper conductors. This improves the thermal insulations around the strands and the heat from the fault can travel further down the wire.

This is why the wire can be damaged some distance on either side of a fault.

Some good advice has been given regarding prevention, but you can also use a quick spray of WD40 or similar water displacing lubricants. This not only helps to keep the contacts clean but can make the joining and separating of the plug and socket a bit easier.

An almost identical fault can occur with domestic 230V plugs and sockets, and the fuse clips inside the plugs, however do not use WD40 on mains connectors.

 

[colin-yorkshire]

hi colin

just a thought is your plugs wired up correctly because the last time I looked the centre black wire was for the rear tail lights

the white wire is the earth.

colin

 

[WatsonJohnG]

Colin Y

Its the 12S plug that is in question and the centre pin is the dedicated fridge earth return

WD 40 may attack certain plastics as my friend discovered in Spain when the plastic on the rear light contacts failed and we had to solder the wires on to the bulbs to get him home

Tri-flow teflon spray is much better but expensive and difficult to get

Wilkinsons sell a teflon spray for bike chains and parts at a reasonable price

It works really well on the steadies as well giving lubrication without picking up grit like grease does!!

 

[Colin_374358138]

Hi,

Have replaced plug and socket.

Have also wired pin 2 to 6 to improve supply. I discovered that 2 was indeed 'live' and passed thru the split relay but was not connected to the caravan.

I have also wired pin 7 to pin 5 to do the same ting for the earth. Brown going into the car was earthed to the car but was doing nothing. Now its got a job.

Things are improved greatly now. Thanks.

Fridge still not a patch on the one we had in the Pageant however. Although you could use the worktop above it as a slow cooker so at least there's a chance to be energy efficient !!!

C

 

[ValA.]

Colin - for what it's worth - it's happened to us several times - and particularly when we've been towing long-distance (ie in France). It can stop your fridge working when towing, and we need that coming back from France, and we usually notice when we hitch up and the fridge light doesn't go on - so we now keep spares of both halves of the socket with us in the van so that we can swap them as soon as it's convenient.

 

[WatsonJohnG]

Val we had the same and so did our friends towing to Spain but linking the pins together as outlined above solved the problem

 

[DJM]

I have to agree with Rod, change car and van to the 13 pin Euro plug and socket and forget about 12S plug / socket problems forever.