Would I be correct in thinking that the requirement, or otherwise, would be defined by a measurement of the impedance between the standpipe and the earth of the electrical installation at the socket outlet? If so, would local equipotential bonding be sufficient?
If so, the previous Poster's point about washing line poles is an interesting one. What happens if you are mowing the lawn and you cut the 2-core cable to the lawn mower? The mower shorts Line and Neutral, becoming live. If the current finds an earth path then the RCD operates. If the operator is the earth path then the aim is to reduce the earth path resistance to reduce the 'touch' voltage, potential difference, between the source of the voltage and earth; faulty lawn mower and earth. What happens if the person is in contact between the mower and a 'spiked' washing line or washing line pole?