In January 2018 Gas Safe Register Technical Bulletin 118 was amended. The changes include new test procedures to keep service engineers safe from electrical hazards when working on gas appliances. The new guidance requires verification of the mains earthing in addition to the safe isolation of circuits before carrying out work on any appliance. Martindale have put together some simple solutions for earth verification, locking off and proving dead.
An effective mains earth is essential for appliances with earthed enclosures. Basic socket testers will not check the quality of the earth, an earth loop impedance test is required. For this reason, the latest edition of TB118 now specifies that an earth loop impedance test should be carried out.
Before selecting the right test equipment for earth loop impedance, it’s worth noting that there are 3 main categories of socket testers, simple, advanced and professional, the key differentiator is in the ability to measure and display either ranges or numerical values for earth fault loop impedance.
Martindale EZ650 Advanced Socket & Spur Tester
All socket testers will show the absence of an Earth; only advanced socket testers such as the Martindale EZ150 / EZ650 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 500 kΩ is normally considered a good insulation level, it’s clear that in this case the “protective” earth to which the appliance is connected will not protect. Given the choice, electricity will flow through the average human (resistance around 2000 Ohms) a lot more easily – and possibly fatally - than through a wire with a resistance of 500,000 Ohms or more. 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.
Often 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 than just an LED fault indicator. Martindale advanced socket testers simplify the whole process of verifying the quality of the earth by using Red / Green LEDs to show whether the loop impedance value is within acceptable limits. The Martindale EZ650 has this capability built-in and is suitable for testing both sockets and spurs, so is ideal for achieving compliance with the latest edition of TB118. It’s also a lot easier to use than a professional socket tester which displays values that require further validation.
The new procedures for loop impedance are in addition to the existing requirements for safe isolation of the appliance before any work is carried out. Safe isolation procedures require the appliance to be disconnected from the supply, locked off and the circuit proved dead. For locking off the supply the Martindale LOKKITGAS1 includes a universal fused spur locking off device, mcb locks with padlock, tag, pen and carry case. For proving dead the Martindale VIPD138 kit includes a simple voltage indicator with no switches ranges or batteries and a matching proving unit and carry case.
For more information on the products and their order codes needed to comply with TB118 click here: