Hole in water pipe and electric cable mystery.

I started getting water coming up from my solid floor - concrete with a 2 inch screed on top.
We opened it up and found a 1/2 inch copper mains pressure pipe running across a live flat pvc electric cable (240V - UK)
The copper pipe was wrapped in some special tape to stop it corroding. The cable was laid bare in the screed.
There was a clean hole - no corrosion - about 1mm (1/24 inch) through the bottom of the pipe directly over the electric cable which also has a matching hole in it.
The circuit breaker did not rip though my plumber said he could hear some electric buzzing when the cable was wet before we isolated it.
How come this hole? The installation is about 10 years old. The damage could not have been mechanical and certainly was not there at time of installation. It looked a clean hole, nearly round - as if done with a drill bit.
Could there have been some interaction between the cable and the pipe. Seems far fetched but what else could it be?
--
Les Desser
(The Reply-to address IS valid)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 13 Jan 2008 01:51:09 +0000, Les Desser

How much seperation between the wire and the pipe?
What kind of wire?

Huh? <g> Never seen such a tape myself, but if you say so...

Current flow was less than the breaker's capacity that's all. But it could have beena problem eventually.

Yes, it could have... Especially if they were touching (which would not have been good...)

Damned gophers... <g> Now they have drills!

Not far fetched at all! But not exactly as you expected it. I don't know (you didn't say) what kind of cable it was, but clearly it had a microscopic flaw in the insulation. THis is not uncommon or unheard of. I'd guess the cable was not rated for direct burrial (I'm unclear of whether this was in the cement or below it, but in either case... the result is the same).
To prevent this from happening again:
1. All electrical cable shoudl be direct burrial rated if going in the ground, or into cement. 2. Preferrable it shoudl be in conduit... Lot easier to pull the cable out and run another one when/if it fails! 3. There are minimum seperation between power cables and other items such as water lines, and non-power wires...
Regardless I'd strongly believe there was simply a micro-pore in the wires' insulation which allowed it to fail, and the close proxminity to the water pipe gave a good path to ground. THe hole in the pipe was elctrolsis which wuold be expected.
If you can't put the entire run in conduit (plastic is best, IMH)) then at least put conduit where it crosses other metal such as rebar, pipes and other wiring...
I'll agree, this is one odd problem! (I've seen it before but not exactly the same circumstances, hence the diagnosis of a micro-pore in the insulation).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Zero
Standard 2.5 mm.sq twin & earth leading to and outside 1 KW light which is hardly ever used.

Apparently standard here - looks a bit like felt impregnated with some very sticky oily substance. All pipes buried in concrete are wrapped in it to stop corrosion.

[..]
They were under at least 1.5 inches of sand/cement screed.
[..]

I assume that must be the conclusion, but still a long shot - each conductor has its own insulation and then there is an outer PVC bonded sheath. And the fault should be directly under the piper, unless the fault is more general - in which case I hope there are no more cross-overs buried under my feet.

Correct
Buried in the cement

A bit late now. I'm digging it all up :(
[...]

Electrolysis sounds right.
[..]

If there is ever a next time, I will watch the contractors!
Thanks for the response.
--
Les Desser
(The Reply-to address IS valid)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Nearby lightening strike?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

CW:
Very interesting conjecture which will be supported if characteristic signs of melting are present. When lightning hits certain sands, "fulgurites" (from "fulgur" for lightning) form and the flow marks are quite evident. But if we have holes that are clean, careful, especially magnified, observation should yield a good conclusion as to what made them.
Regards,
Edward Hennessey
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Unfortunately the plumber has taken away the old pipe but my recollection is of a regular round hole with clean edges with a slight elongation of the hole at one point. No signs of depression as from a puncture nor any corrosion or melting.
--
Les Desser
(The Reply-to address IS valid)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I have never heard stuff like that.
http://www.planorealestateadvisor.com http://www.planoralty.blogspot.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Not where we are :) (London)
--
Les Desser
(The Reply-to address IS valid)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Les Desser wrote:

No lightning in London?
--
Art

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Just rain :) Thunderstorms very very rare.
--
Les Desser
(The Reply-to address IS valid)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.