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Beware of socket testers not detecting poor earths

Electrical installations need to be regularly checked to ensure they remain safe, according to the Health and Safety Executive: simple socket testers do not identify dangerous poor-earth faults

Beware of socket testers not detecting poor earths

This is especially important in areas where electrical sockets or wiring are likely to become damaged.

"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" warns the HSE.

"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".

Steve Dunning, managing director of Martindale Electric said: "Martindale has introduced the E-Ze 150, a socket tester that gives an accurate indication of earth loop impedance in bands.

Now, users can buy a small plug-top shaped socket tester testing the quality of the earth for less than GBP50".

There are three types of socket tester: simple, advanced and professional.
Simple socket testers can detect various faults but cannot identify some extremely dangerous poor earth faults.

Advanced and professional socket testers can measure the earth fault loop impedance on indicator lights or a digital display.

Professional socket testers with digital displays cost upwards of GBP250, and are bulkier than plug-top testers, usually with a separate plug and power cord.

On the other hand, not all yellow plug-top testers with flashing lights are the same, and the Martindale E-Ze 150 is superior in that it provides the all-important earth loop impedance test.

Socket testers are typically used, amongst others, by maintenance personnel and equipment installers who need to ensure that the socket is safe.

This also applies to maintenance personnel carrying out portable appliance testing (PAT).
Equipment installers also want to check that a socket is safe before installing a new photocopier or a new vending machine, or before subsequent servicing of installed equipment, because inevitably the equipment will have to be powered up at some point.

Prior to performing a professional earth loop impedance test, an electrician may equip an apprentice with a simple GBP12 socket tester to help him check that the wires are the right way around after he has wired his circuits up.

It detects the absence of an earth, but where there is an earth, it does not test that the earth is good.

By contrast, the Martindale E-Ze 150 socket tester can be sourced by electricians and installers for under GBP50, a small price to pay for testing the earth, not just checking for the right polarity, thereby cheaply ensuring that the earth has been pre-tested by the apprentice carrying out the work.

"No other plug-sized socket tester can perform the earth loop impedance test," continued Dunning "The Martindale E-Ze 150 measures earth loop impedance without tripping the installation RCD.

Qualified electricians know they have to perform this test and will probably use professional 16th/17th Edition installation testers that give measurement readings.

Maintenance personnel too need to be aware that a simple socket tester cannot determine that a socket is safe.

The same goes for handymen, DIY hobbyists, office managers, and installers of equipment such as PCs, photocopiers and vending machines".

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