Extranous conductive parts

[newfutile]

During an EICR I have come across a metal tap and copper pipes supplied by a blue plastic pipe.

This measures 0.022 MegOhms, this is directly under the consumer unit which is metal.

Is this an extranous conductive part?

 

[Avo Mk8]

Come on chaps, basic physics here !
Resistivity is the resistance between opposite faces of a cube of the substance. You can make the cube whatever size you like and you get the same value.
For a 1/2" (15mm) pipe, the cross sectional area is 174sq mm, so roughly 17.4cm of pipe will equate to the resistivity figure.
1 metre of that pipe will measure 100/17.4 = 5.7 times the resistivity etc.
At least that was taught to me over 50 years ago - maybe it's all changed now

PS I haven't watched the video yet so maybe that says different??!

 

[Pretty Mouth]

You can make the cube whatever size you like and you get the same value.

I don't think this is correct Avo. By my calculations, a larger cube will always have a lower resistance across the faces?

 

[brianmoooore]

Square, not cube.
........

 

[Avo Mk8]

Square, not cube.
........

Ah yes. Memory fail again!

 

[cliffed]

imagine most Sparks doing a test to prove its ECP especially in the newer build houses where plastic cold piping enters the house, I doubt it.
This is one reason why we use to install a MBPC to gas water etc BELT & BRACES

 

[HappyHippyDad]

I've relooked at the site I was getting my figures, It's a little confusing, but It looks like the 1000ohms - 5000ohms for unfiltered tap water may be per cm as you suggest. This would then fit in with JW's video as well. thanks for pointing that out LMO.

 

[HappyHippyDad]

imagine most Sparks doing a test to prove its ECP especially in the newer build houses where plastic cold piping enters the house, I doubt it.
This is one reason why we use to install a MBPC to gas water etc BELT & BRACES

If the resistivity of tap water is 1000ohms p/cm (worst case) then I cant really see it being a problem in a domestic house. You would somehow have to have something that had almost direct continuity (downstream) with the MET and the water within 22cm's of the plastic pipe connection.

Now with the OP's example, the resistivity may be around 200ohms p/cm. meaning the 22cm's jumps to around 1meter. Possible that those plastic pipes become metal in the box they are hidden in and have a very good connection to earth. Still seems unlikely though.

I really want to know how the OP gets a figure of 0.22Mohms now!!? OP, could you please dismantle the box and dig up a section of earth and concrete floor please, down to depth of 1.1m?

 

[LastManOnline]

I've relooked at the site I was getting my figures, It's a little confusing,

Confusing sums it up well.I looked up several sites and quite frankly you could make an arguement for either case.But the advantage of discussing "tap water" is that we all have easy access to it.I myself have taken my own IR tester to it on several occasions over the years and my readings were somewhat similar to J.W.,s (give or take a few thousand ohms)

 

[LastManOnline]

If the resistivity of tap water is 1000ohms p/cm (worst case) then I cant really see it being a problem in a domestic house.

correct.It is,nt.

You would somehow have to have something that had almost direct continuity (downstream) with the MET and the water within 22cm's of the plastic pipe connection.

I think the issue may lie with the "Cat 5" label.That is as far away from tap water as you can get.
Bearing in mind that the resistivity of water drops considerably when pollutants are introduced to it ,that would be my first area for investigation.
Is it actually allowed to have a "Cat 5" tap in a domestic scenario in the UK?

 

[newfutile]

I think it’s fed from a tank in the open loft area (no ceiling) of the bin store so it’s likely full of dead flys and whatever , why this was done I have no idea , I’m not sure if the tank is fed by mains water .