Socket testers are designed to identify a variety of faults with socket wiring, but many commonly used socket testers cannot reveal a poor earth that could lead to someone being killed.

Why is a socket with a poor earth dangerous?

A socket might have a poor earth for years with no visible signs. However, when an appliance plugged into it develops a fault, earthed metalwork can become permanently live at a dangerous voltage. This could give the user a fatal electric shock, or cause a fire.

Socket testers

There are three types of socket tester:

Simple socket testers are designed to detect various faults. However, these cannot identify some extremely dangerous (poor earth) faults.

Advanced socket testers and Professional socket testers are designed to detect a range of faults, and can actually measure the effectiveness of the earth (the Earth Fault Loop Impedance). They show the Earth Fault Loop Impedance on indicator lights or a digital display.

Safety Checks

Electrical socket outlets should be maintained in good condition; not loose, cracked, damaged by heat, or electrically unsafe. If you have any doubts about the safety of a socket, you should prevent it being used, and have it examined and repaired by a competent person.

People using socket testers as a part of a safety check should understand the importance of the Earth Fault Loop Impedance value, when to take further action, and what to do.

Simple socket testers that cannot measure the Earth Fault Loop Impedance could mislead the user into believing the socket is acceptably safe when it is not.

If your socket tester cannot display the Earth Fault Loop Impedance, it should not be used to check whether a socket is adequately earthed and safe to use.