From Gerry Harant
The phenomenon of vibrations when you draw your finger or some other sensitive part of your body over nonearthed electrical devices connected to the mains is clearly electrostatic, because it does not require the appliance to be metallic (Letters, 2 December and 13 January). It occurs strongly on the outside of ceramic “electric jugs” filled with water heated by a naked element or, as mentioned by Don Hinson, on electric blankets.
This explains why it is only felt when “stroking” the equipment. While stationary, the contact between hand and surface prevents the variation in attractive force caused by the cyclic nature of the potential resulting in any movement that can be felt. When rubbing the surface, this variation in attraction results in cyclically changing friction between skin and equipment which feels akin to a tingle, but is actually mechanical in origin.
While the equipment displaying the vibration is generally perfectly safe, any real tingle felt when touching rather than stroking mains-connected electrical gear should be investigated immediately.
