Don’t Ignore The Earth Wire
From a safety perspective, the most important wire in any installation is the earth wire make sure it’s properly connected to an earth point that is properly earthed.
This may sound obvious but in some locations in some applications establishing earth can be tricky to do. Making this harder is that the device you’re installing or repairing is likely to work happily even if it’s not earthed – the first you’ll know about an earth loss you’ll be flat on your back or worse.
The only mains powered devices (this includes those run by a transforming plug pack) that don’t need to be earthed are those that bear the label ‘double insulated – do not earth’.
The standard colour of the earth wire is green and yellow – never use this colour for any other wire than earth and never connect this wire to anything but an earth pin/point. Bear in mind, however, if you’re battling your way around an old site and you run into a solid green wire, this could be earth also.
The presence of earth ensures that should a live wire or component touch the metal chassis/housing of a security system or device, it will be carried to earth through the wire, not through your body.