Technical Bulletin 118 (TB118) from the Gas Safe Register - updated on 30th January 2018 - sets out the steps that should be taken by gas engineers to properly isolate appliances that use an electrical supply. This includes the majority of appliances in domestic and commercial environments. Safe electrical isolation is vital to ensuring that engineers do not receive a potentially dangerous electric shock, which can cause anything from mild discomfort to death.
Legislation
In addition to discussing the consequences of electric shock, TB118 identifies legislation that is pertinent to the safe isolation of gas appliances. Namely, these are the Health and Safety at Work Act 1974, which imposes a duty on employers to ensure the safety of employees and others, and the Electricity at Work Regulations 1989, which states that all conductors must be dead during work unless it is unreasonable to be dead, reasonable for an engineer to work on or near said conductor, and suitable precautions are taken. The Health and Safety Executive provides further information on electrical testing during servicing and repairs on domestic appliances in Engineering Information Sheet No. 35 Revision 1.
Creating a Safe Work Area
Creating a safe working area is crucial at all times and TB118 provides specific advice on this when it comes to electrical isolation. Firstly, preventing third parties access to an appliance is very important so it is often a good idea to erect a temporary barrier. Other suggestions include asking for children and pets to be kept away, informing everyone in a property of any dangers arising from testing, and making sure you never leave an appliance unattended when in a dangerous state. Another simple, practical step is to make sure there is sufficient space around an appliance so that, in case of an electric shock, you are not restricted and can quickly move away from the live conductor.
TB118 also recommends that the earth path of Class 1 appliances is properly tested before starting work. This is because adequate protective earthing is required in fault conditions. It is therefore advisable to carry out an earth loop impedance test to obtain a resistance value for the earth path. An instrument capable of providing an actual numeric reading - as opposed to a simple ‘Go/No go’ indication - should be used and the customer must be informed that work cannot go ahead if there is a problem that needs to be rectified.
A Safe Isolation Process
TB118 sets out a guide to the safe isolation process as well as providing specific advice on various aspects of the procedure. Notably, single-pole or non-contact voltage testers should only be used to find live conductors and do not prove that equipment is dead whilst a multimeter should never be used for proving dead. Instead, a two-pole voltage detector complying to BS EN 610101-1 is recommended. The Technical Bulletin also discusses the importance of safely isolating equipment so that it cannot be re-energised. This may include putting up warning signs, adding locking devices, removing fuses or locking fuses and switches open.
A summary of the Technical Bulletin 118 guide to a safe isolation procedure is set out below:
- Obtain permission and make sure it is safe and acceptable to isolate the gas appliance. Remove all load from the circuit by switching off any switches. Remove fuse carriers and/or fuses from switched fuse connection units and lock the carrier open if it does not come out. The engineer should keep hold of the fuse. Any socket outlets should be switched off and the plug removed. If the socket is adjacent to the appliance and visible, there is no need lock out. If the plug is not visible, it should be locked off with an appropriate device that prevents connection to a socket.
- Test the two-pole voltage indicator on a known voltage course before use, typically a proving unit of an appropriate voltage.
- Test for voltage between E-L, N-L, and E-N with the voltage detector. All other terminals should also be proved dead. It is important to remember that when checking between earth and live conductors, the earth connection should be made first and removed last to prevent the appearance of dangerous voltage at the tip of the indicator.
- The voltage indicator should then be reproved by once again testing on the known voltage source.
In addition to this procedure, a risk assessment must be carried out before testing and PPE employed as needed to ensure safety. A wide range of different instruments are available for both locking out and voltage detection but there is a specific Martindale TB118 Gas Engineer’s Electrical Test Kit that has everything needed to follow the bulletin’s recommendations.
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