DERMAVIT Diamond Shield IE Zapper Bedienungsanleitung Seite 30

An earthing cable and an enclosed power socket tester are available as optional
accessories.
The good effect of the earthing (so called negative ions) occurs only if the power
socket is properly earthed. Be sure to check this with the power socket tester.
Warning
The use of the earthing plug (or any other electrical appliances) to an incorrect
power socket can be perilous.
Do not use the earthing cable during a thunderstorm.
Diamond Shield
page 30
Instruction Manual