This message I posted yesterday has been totally lost amidst an endless sea of totally off-topic messages (which I imagine most people are ignoring), so I thought I would start a new topic in case anyone has any interest in what I wrote......
OK, I’ve done my best to ‘do the experiment’ ....
Most of my cellar has a floor of (in many cases cracked) unglazed quarry tiles, about 1 cm thick, laying directly on soil and, at this time of year, they are decidedly ‘very wet’. I have just tried putting a roughly 9” square of copper sheet on the wettest part, weighed down (for ‘good contact’) with a sledge hammer.
By various nefarious means (details of which I will not describe here!) I have estimated that the resistance of the path to earth through this plate is about 10.4 kΩ (when measured at ~240V AC). If one adds on a notional 1 kΩ for body resistance, this would equate to a current of about 20.2 mA through a person who was standing on this floor with bare feet and touching a 230V source.
That’s certainly more than high enough a current to be worried about, but it has to be realised that this figure relates to a situation which is probably far ‘worse’ than one would ever be likely to encounter in almost any real-world bathroom. In the presence of even the slightest apology for 'floor covering' (and/or any 'anti-damp' measures under the tiles), it is likely that the current would fall to an extremely low, quite probably 'negligible', figure.
Kind Regards, John
It would probably be a pretty low-impedance, possibly pretty dangerous, route to earth. .... However, I would think it must be extremely rare to have a ground floor bathroom with a concrete floor built straight onto earth with no DPM or suchlike, and with absolutely no floor covering. The moment one has virtually any floor covering (or any 'anti-damp' measures in, or under, the concrete), the path to earth probably usually becomes high enough for any current through a person not to be, in itself, particularly dangerous.So what's the typical conductivity of a damp concrete floor - say in a bathroom ? Is that enough to cause a dangerous current to flow through someone stepping out of the bath/shower with wet bare feet and touching a tap ? In this case I can see an argument that electric U/F heating will increase safety since it will raise the floor potential to the internal false earth level.
OK, I’ve done my best to ‘do the experiment’ ....
Most of my cellar has a floor of (in many cases cracked) unglazed quarry tiles, about 1 cm thick, laying directly on soil and, at this time of year, they are decidedly ‘very wet’. I have just tried putting a roughly 9” square of copper sheet on the wettest part, weighed down (for ‘good contact’) with a sledge hammer.
By various nefarious means (details of which I will not describe here!) I have estimated that the resistance of the path to earth through this plate is about 10.4 kΩ (when measured at ~240V AC). If one adds on a notional 1 kΩ for body resistance, this would equate to a current of about 20.2 mA through a person who was standing on this floor with bare feet and touching a 230V source.
That’s certainly more than high enough a current to be worried about, but it has to be realised that this figure relates to a situation which is probably far ‘worse’ than one would ever be likely to encounter in almost any real-world bathroom. In the presence of even the slightest apology for 'floor covering' (and/or any 'anti-damp' measures under the tiles), it is likely that the current would fall to an extremely low, quite probably 'negligible', figure.
Kind Regards, John