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Potable water is not in electrical terms, conductive enough in pipes to be an ohmic issue
When I first moved to Hilltop, I measured the Line-Earth impedance at an otherwise isolated metal stop valve terminating the incoming of plastic water supply main at least 40m long (from the cast iron water main in the road), and I think I measured a value of 1000 ohms (although some of the conductivity could have been from the brickwork the stop tap was leaning against). This gives a potential fault current of 240mA, compared with the 30mA trip current of an RCD. With a short section (say 500mm) of plastic water supply pipe used to insulate a metal outside tap from the copper pipework inside a house with a PME earth, I would expect a higher maximum leakage current in the event of a CNE conductor failure, and so the tap should ideally have its own earth spike!!
 

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Potable water has a Maximum conductivity of 800micro Sieverts per cm. Do the maths for your 40m supply.

The Line Earth impedance as measured at 1000 0hms clearly was measuring an additional parallel path to earth!!
 

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Potable water has a Maximum conductivity of 800micro Sieverts per cm. Do the maths for your 40m supply.

The Line Earth impedance as measured at 1000 0hms clearly was measuring an additional parallel path to earth!!
Sorry wrong units duh
 

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A calculation.

Using 50millisiemens/m as a realistic but high value for potable water conductivity, a 32mm internal diameter supply pipe 40m long has a conductance of 1 x 10 -6 mho, or 1MOhm. With a 250V supply, leakage current would be 0.25mA.

The same calc but using a 200mm long hose with a bore of 14mm gives a leakage current of 9.6mA.
Thats the external tap sorted.
 
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