Body voltage - should it be measured?
Should you use earthing products and should you measure body voltage?
Alasdair Phillips, director of EMFields and Powerwatch and designer of the EMFields meters we stock, shared his views with us. Alasdair is an internationally-respected authority on testing electromagnetic fields. He said:
'I have real problems with the measurement of “body voltage” as it is usually measured and I need to answer it in a somewhat long-winded way.
'Electric fields are the measure of the electric field potential between two points and our meter measures what your body will be experiencing. Any conductive body (e.g. human, animal or plant or tree) in an electric field will distort it and usually enhance (increase) the level measured. The enhancement (increased V/m) is the reason that lightning often strikes trees sticking up above the landscape rather than directly on to the ground below.
'If your feet are on or close to live mains voltage wires (whether visible of the floor or under the floor) then measuring to an Earthed radiator will give a high reading. The electricity is coming up through your body and returning to the radiator, not the other way around.
'That is why our electric field measurements meters (the original PF4 and now the PF5) are calibrated to measure electric field relative to the person holding the meter. That way you get a correct reading of your actual exposure to electric fields.
'Now a ‘body-voltage’ measurement using a sensitive high impedance voltmeter (as is normally used) measures the voltage between a person’s body and “earth” or “ground” – usually the electrical safety earth in the building’s wiring. Then they stand or sit the person on an earthed sheet and, voila, the reading goes down to near zero. Of course it does(!) as the two meter measurement connection leads are now effectively both connected to “earth”. What it does not show you is that in most buildings that have electrical wiring in them, the electrical current flowing right through the person goes up – often substantially. This is because they now look like the tree did to the lightning and any electric fields will target them as a large earthed object and then a capacitively coupled current will flow through their bodies to earth. Very unwise, in my opinion.
'A sort of converse is how birds can perch on high-voltage overhead wires without being electrocuted and how people can even work on live 400 kV overhead lines provided they are in a cage or body-suit that is connected to the high-voltage cable – the voltage across their body is effectively zero. However, if you measured their body-voltage to Earth it would be 400,000 volts!
'We first noticed this about 30 years ago when we started work on ways of reducing peoples’ exposures. When we earthed their beds (either underneath the bed or via a conductive earthing-sheet) their body current went up due to fields coming from the wall and even, to a lesser extent, from the ceiling. It is OK of you put a full earthed conductive canopy over the bed as well, as that means that the person is lying fully inside an earthed tent/enclosure. That is why we have real problems with <some practitioner's> simplistic methods of earthing people and beds, although some people report that it has greatly helped them. It will do if they remove all mains electrical equipment from around their bed and move the bed away from any wall. Earthing to the real Earth is helpful, especially outside through bare feet on the real Earth. It also seems good inside a building if the electrical earth is “clean” and if the person is inside a fully earthed enclosure/tent.'
Please note that there are alternative views on measuring body voltage, for example those of the Earthing Institute.