Live earth on 3C&E cable.

[Satori]

Was having a little look under the floorboards beneath the hot water tank earlier in anticipation of wiring up a new shower and I spotted a concealed junction box connected to a piece of three core & earth cable whose sheath was broken. On closer inspection I decided - compliments of my recently diagnosed DIYNot Anxiety Disorder™ - to check whether the exposed conductor was live. It turned out to be a circuit protective conductor with 70 volts between it and the adjacent copper water pipe. The latter has a sound electrical bond to the main earthing terminal. It appears the blue conductor has been pulled out of the cable and is terminated in the junction box.

After a bit of head scratching I realised the unsheathed earthing conductor wasn't part of my installation but belongs to the neighbour in the apartment below. I'm not sure whether to quietly steal some of his electricity or politely point it out.

Few pictures to illustrate:

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• Satori
• 8 Oct 2013
• 1

The sheath on what I have called "cable 2 (b)" appears to have been ripped open presumably by the removal of the blue insulated conductor.

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• Satori
• 8 Oct 2013
• 1

Here looking towards cables 1 and 2b (left to right).

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• Satori
• 8 Oct 2013
• 1

And here showing that part of the sheath which initially caught my attention.

Is there an obvious explanation for this reaching a voltage to earth of 70 V?

Thanks.

 

[securespark]

It's not connected or not connected effectively to earth.

What did you use to find the 70V?

Try testing between that cable's CPC and a socket cpc or fitting screw. This will give you a more reliable reading.

 

[Satori]

Tested it with a Fluke 289. The impedance between the pipe and the main earthing terminal was 0.03 ohm. Will try it with a nearby socket tomorrow.

 

[ban-all-sheds]

Test it with something other than a high impedance DVM.

 

[JohnW2]

Test it with something other than a high impedance DVM.

Good advice, but if he then finds that there is little or no voltage (with a low impedance testing device), that would presumably still suggest that his neighbour's CPC is probably not satisfactorily earthed, if he's seeing 70V w.r.t earth with a high impedance meter, wouldn't it?

Kind Regards, John

 

[ban-all-sheds]

Yes