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Doh, Yes I was trying to use the example in the regs for working out what resistance would be needed for an earth electrode and a car charger on PME, but didn't know what figure to use as the load
The average house will normally have an average demand less than 20A, maybe peaking around 30A occasionally. So I've run that equation for 20A 30A and 40A
For 20A resistance would need to be less than 5ohms
For 30A, 3.35ohms
For 40A, 2.51ohms
Depending on where you are in the country these may or may not be achievable figures.
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This is from one of Chris Kitcher's books:
It is a common belief that water in pipe work will conduct: in fact the current which will flow through water across a plastic fitting filled with water is very small.
To find out how much current would flow I carried out a controlled experiment using two short lengths of copper pipe. These were joined using a plastic push fit coupler. Once fully pushed home the pipes were no more than 2mm apart (Figure 4.24).
The pipe was then filled with tap water and the ends were connected to a 230v supply. The current flowing was so low that my clamp meter would not measure it, as it only measures down to 0.1mA. The current flow would increase if the water had central heating additives in it, but not considerably.
Yes, he demonstrated that exact experiment to us during the 17th edition course, it was all very impressive but I'm not sure how relevant it is to the point.
There was no mention of how long the water had been in the apparatus or how pure/impure that water was. So there was absolutely no scientific basis to the experiment leaving his conclusion completely useless.
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