Lucky escape? What's happened to this pull-cord switch?

[^woody^]

This is about 18 months old. Cable is 10mm and the shower is 8.5kW. Switch is an MK 50A

Can anyone give a likely cause of this. I don't think it is overloading, and I am curious as to the corrosion and the trace of some liquid in the pattress.
There is no evidence of rodents in the loft, and no access to the pattress anyway. If condensation why the staining and smell

But did the corrosion come first or did insulation come off first

Insulation was sound and right up to the connector when fitted

1. Here is the switch when dropped from the ceiling. The white bits are just plaster dust done when removing.
The black/red cable is the supply from the CU, and the new blue/brown is the load to the shower

Ceiling pull cord

• ^woody^
• 17 Jun 2012
• 1

Its an MK 50A

The shiny bits are some sort of liquid, although there is no evidence of any cause in the loft above

The load neutral insulation is heat damaged, but also has mechanical damage

The blue neutral has corrosion and the insulation has come away from the block - the insulation was there when fitted

All connections are very tight

2. Cables in more detail

Cables

• ^woody^
• 17 Jun 2012
• 1

Black/red = supply, brown/blue = load<br>Heat damage to black neutral, corrosion to blue and...

3. Cables in the fitting

Note the liquid

Cables in fitting

• ^woody^
• 17 Jun 2012
• 1

Shiny bits are liquid<br><br>Bottom corroded cable is the neutral on the load side

4. Inside the ceiling pattress

The liquid is yellow/brown, and it smells. Note corrosion to earth block and cable screws

Liquid in ceiling pattress

• ^woody^
• 17 Jun 2012
• 1

Smelly liquid, does not seem like water and corrosion to earth point

5. Corrosion to load neutral

Also it seems mechanical damage and loss of insulation - this was just hidden by the outer sheathing

Mechanical damage and corrosion

• ^woody^
• 17 Jun 2012
• 1

Neutral on load side

 

[sparkydude]

Loose neutral connection is the cause i am afraid. That is a common problem with pullcords that have a single screw clamping down onto a multi stranded cored cable. Especially on newer high current appliances

The liquid you refer too will have been caused by the heating action of the loose connection melting the plastic of the PVC and releasing an acidic compound, this will also account for the corrosion on the cores.

Nick

 

[wingcoax]

Can't find the emoticon,but WHAT HE SAID. A very(unfortunately) common problem.

 

[^woody^]

Thanks.

I was hoping that it would be a "simple" explanation

 

[wingcoax]

That is as simple as it gets. The only cure is to regularly inspect and re-tighten.

 

[ban-all-sheds]

Can't find the emoticon,but WHAT HE SAID.

http://www.pushupstairs.com/images/emoticon/eviewer.php

http://helmies.org.uk/

http://ebassist.com/forum/misc.php?do=showsmilies

http://www.kirupa.com/forum/misc.php?do=showsmilies

http://www.clicksmilies.com/

http://www.thestylemachine.com/smileys.html

 

[wingcoax]

Thanks BAS

 

[ban-all-sheds]

The liquid you refer too will have been caused by the heating action of the loose connection melting the plastic of the PVC and releasing an acidic compound, this will also account for the corrosion on the cores.

I'm pretty sure that PVC doesn't release acidic compounds until it actually burns.

The green gloop here is more likely to be Di Octyl Phthalate

 

[RF Lighting]

Unlikely with modern cables. AFAIK it was only a problem with cables manufactured 40ish years ago.

 

[ban-all-sheds]

You may have a point there...

Although I suppose it could happen again, with a cost-cutting manufacturer buying sub-standard PVC.

 

[^woody^]

I've got experience with green goo (via personal injury claims), and there was non in this case. It was purely a green patina on the exposed copper

I was curious as to what occurred first - was the liquid the cause or result of the burnt cable and did it contribute. But now I know.

There was never any burning smell though