Choosing the right socket tester

All socket testers check that the earth, live and neutral are the right way round (called polarity testing). Some offer added features – they may include a buzzer in addition to LEDs to indicate a good socket or they may show a combination of indicators to identify which particular fault type is present. 

There is one fault that a socket tester and indeed no other piece of equipment can easily find – the swapping of the Earth and Neutral wires. This is because the earth and neutral are common at the substation, (if not closer), so electrically they are indistinguishable. 

When selecting a socket tester it’s important to understand the different types available and their capabilities and limitations. 

Socket tester categories 
There are various categories of socket testers, ranging from simple checking devices to more advanced devices with multiple functions. The key differentiator is in the ability to measure and indicate earth fault loop impedance. 

	Simple (CP501,BZ101)	Advanced (EZ365)
Capabilities
Indicate functional socket	✓	✓
Detect line / neutral reversal	✓	✓
Detect presence of earth	✓	✓
Display range of earth loop impedance values	X	✓
Live Neutral supply swap	X	✓

All socket testers will show the absence of an Earth; However more advanced testers such as the Martindale EZ365 will show you how good your earth is. 

This differentiation is important as some simple socket testers on the market have been seen to show an earth as good even when the impedance is as high as 500kΩ. As 0.5MΩ (500 kΩ) is normally considered a good insulation level, it’s clear that in this case the “protective” earth will not protect. 

Socket Testers 

A reliable earth loop impedance measurement is important to ensure that the over current protection devices achieve a fast enough disconnection time to avoid electrocution. In the case of an earth fault, loop impedance values must be less than those specified in the BS7671 Wiring Regulations Amendment 3:2015. Earth loop values higher than a few ohms can cause problems with disconnection times and therefore socket testers capable of indicating earth loop impedance values in this range reveal a lot more about the electrical safety of the installation.
 

18th Edition Testing and Verification 

It’s important to appreciate that socket testers are not an alternative to the full verification of wiring installations. However, as a first line indicator to identify potentially unsafe installations and wiring faults, socket testers offer a fast and effective solution when properly specified. They can also be particularly useful as a service tool in identifying potentially unsafe conditions prior to carrying out work on existing installations and appliances. For more information on the use of socket testers including their benefits and limitations, see the application notes. 

For information on professional loop testers and multifunction testers suitable for carrying out all the tests needed to verify the safety of domestic, commercial and industrial wiring installations according to the18th Edition Wiring Regulations, see our  Multifunction Installation Testers.