Calculating broken PEN touch voltage with backup earth electrode

[timhoward]

The take-away fact here is that if a rod is expected to sink a realistic installation neutral current without the touch voltage from the broken PEN to real earth exceeding 50V, it has to offer a resistance lower than can usually be achieved. For Uo=230V and 50V touch, it's (50/(230-50) * (230²/P) ohms, where P is the installation load (or unbalance, if 3-phase) in VA.

Thank you very much.
I think I recognise the 2nd half of the formula as P=V^2 / R rearranged? (though using real power not apparent power)
I'll muse the first half later as don't quickly get why divisor is 230-50

 

[UKPN]

Thank you very much.
I think I recognise the 2nd half of the formula as P=V^2 / R rearranged? (though using real power not apparent power)
I'll muse the first half later as don't quickly get why divisor is 230-50

He doesnt do the bonding but installs a rod to reduce the "touch voltage"