Technical Bulletin 118a
Safe to touch and/or safe isolation and proving electrically dead on low-voltage single-phase supplies (below 1000 volts)
Date issued: 1 February 2023
Date of review: 1 February 2025
Note: This version of Technical Bulletin (TB) 118 replaces the version originally published on 30 January 2018, which is now withdrawn. This version has been reviewed and revised where appropriate to ensure that it remains both current and relevant.
This TB provides information and guidance only relating to safe-to-touch and safe isolation procedures on low-voltage single-phase supplies when carrying out gas work. A version of this TB concerning multi-phase supplies and earth loop impedance will follow. This TB should be read in conjunction with other recognised and approved guidance. This TB has been developed with a committee made up of industry members and will be reviewed periodically.
Time should be taken before attending site and before work starts to assess the risks associated with the work to ensure that those involved have the necessary competence and equipment to work safely.
The health and safety enforcing authorities in all geographical areas covered by Gas Safe Register, ie Great Britain, Northern Ireland, Isle of Man, Guernsey and Jersey, regard the guidance in this Technical Bulletin as a best-practice requirement and would expect all Gas Safe registered businesses/engineers to apply the requirements of this TB when and where appropriate circumstances/relevant appliances are encountered.
For details of current health and safety legislation, gas safety legislation, building legislation and industry standards for the geographical areas covered by Gas Safe Register, see the Legislative, Normative & Informative Document List (LNIDL)(1) by logging into your online account at: www.GasSafeRegister.co.uk/sign-in
Introduction
Electric shock is defined in the current version of BS 7671 (IET Wiring Regulations) as a dangerous physiological effect resulting from the passage of electric current (amps) through the human body.
Sometimes this passage of current can lead to nothing more than some small discomfort to the person receiving the shock, while at other times it can result in fatality of the person(s) receiving the shock.
The guidance in this TB should be applied in premises supplied with low voltage in a single-phase provision. The following 1-12 steps correspond to the guidance in the diagram found in Appendix 1 of the Technical Bulletin.
STEP 1: WORKING ENVIRONMENT
Check with the responsible person that it is acceptable to isolate the equipment/circuit, and that any other electrical items connected to the circuit are OK to be shut down.
STEP 2: SAFE TO TOUCH (EQUIPMENT)
Select an appropriate no-contact voltage detector. The device must be checked for damage and verified on a proving device or known live source. All test equipment should be of a proprietary design and be manufactured to BS EN 61010-31, BS EN 615572 or BS EN 61243-3.
No-contact live circuit detectors (voltage sticks): Due to several fatalities over the years, it has become custom and practice in the gas industry to use a single-pole or no-contact live-circuit detectors (sometimes referred to as voltage sticks). These are used prior to touching appliance casings, gas and water pipework to ensure a dangerous voltage is not present due to a fault condition.
HSE Guidance Note GS38 (Electrical test equipment for use on low voltage electrical systems, fourth edition) states that no-contact live circuit detectors (voltage sticks) should only be used for identifying live equipment, not for proving that it is dead. Therefore, further appropriate tests must be used to prove equipment is electrically dead prior to undertaking work.
In all cases, manufacturers’ instructions must always be followed when using a no-contact live-circuit indicator.
Two-pole voltage indicator/test lamp: Because it is vitally important to ensure that the appliance/equipment is electrically dead before any work commences, an approved voltage indicator or a test lamp will be required to prove this.
HSE recommends that a multi-meter is not used for proving dead (HSG85(2) ).
Before using any voltage indicator or test lamp, it is vitally important to test them on a known supply or proving unit before and after use.
Proving unit: This provides a reliable and repeatable means of supplying a voltage reference to check the function and serviceability of safety-critical test equipment, ie, voltage detectors and test lamps.
Due to proving units supplying lethal voltage levels, relevant manufacturers’ instructions must be followed when using these devices.
STEP 3: SAFE-TO-TOUCH (PROCEDURE)
Use the no-contact voltage detector to perform a sweeping scan of all exposed surfaces of the appliance casing and all exposed metal pipework, both connected to and in close proximity to the appliance/gas meter installation.
If the no-contact voltage detector indicates the presence of voltage, stop the procedure immediately and inform the customer that the installation requires the immediate attention of a suitably electrically competent person.
If a fault is found, the follow-up actions on site to ensure the installation is electrically safe will depend on the situation. Therefore, the engineer will need to carry out a suitable risk assessment, and/or obtain advice from a suitably electrically competent person. An example of a notice to leave with the responsible person is given in Appendix 2.
Where the no-contact voltage detector does not indicate any voltage on the appliance casing/gas meter and any connected/close-proximity pipework, return the device to a known live source of power – eg, a live 13A socket-outlet – and confirm that the device indicates the presence of 230V (indicated by an audible tone and/or illumination of the device tip).
STEPS 4-8: SAFE ISOLATION
Identify the point of isolation for the appliance to be worked on. Select an approved two-pole voltage indicator (GS 38 approved) and verify it is working, either on a proving unit or known live supply.
Verify that the appliance is functional (if this is not the case, checks may be required to verify the circuit), and that it is supplied by only one power source. Once this is done, proceed to isolate the appliance by:
• Turn off the circuit by the switched fuse connection unit (SFCU)
• Remove the plug from the socket-outlet
• Remove the fuse
• Circuit-breaker (MCB) on the consumer unit
Fit an appropriate locking-off device and warning label for isolation and identified work to the isolation point. The person carrying out the work should retain the key.
Note 1: SFCUs are not always double-pole
Note 2: It is important to ensure that all other terminals, such as pump over-run, switched live and any external connections are ‘dead’
Important: The neutral coming into a property with a TT earthing system may not be at earth potential. Therefore when working on TT systems it is essential that the means of isolation being used disconnects all the live conductors (line and neutral).
STEP 9: LOCKING-OFF METHODS
Plug and socket-outlets: Switch off the socket outlet (if switched) and remove the plug from the socket supplying power to the appliance/installation being worked on. Remove the plug fuse if at all practicable. If the plug and socket outlet is not adjacent to the equipment being worked on, the plug will need to be secured against inadvertent reconnection by another person. There are several proprietary devices available for this.
Switched fuse connection unit (SFCU): Switch off the SFCU (if switched) and remove the fuse. Using a proprietary locking-off device, secure the fuse carrier in the open position. The removed fuse (and the key to any padlock(s) used) is to be retained on the person of the individual carrying out the work. Do not leave the fuse in open view/adjacent to the SFCU.
Consumer unit MCB: Switch off the MCB controlling the circuit supplying the appliance/installation being worked on. Lock off the MCB using a proprietary lock-off device. The key to any padlock(s) used is to be retained on the person of the individual carrying out the work. Insulation tape must not be used to secure an MCB in the off position.
Consumer units: Where fused consumer units are encountered, remove the fuse (and if applicable the fuse carrier) that controls the circuit supplying the appliance/installation being worked on. If the fuse carrier cannot be withdrawn, a lockable fuse insert shall be used. The removed fuse (and the key to any padlocks used) is to be retained on the person of the individual carrying out the work. Do not leave the fuse in open view/adjacent to the consumer unit.
Warning notices: Regardless of the method adopted to lock off the source of supply, warning notices should also be posted to inform others that work is being carried out on the electrical system.
STEP 10: VERIFY CIRCUIT IS DEAD
Verify the appliance is isolated. Use the approved two-pole voltage indicator device to verify the circuit is dead by testing between all conductors. Test between:
1. Earth – line
2. Earth – neutral
3. Neutral – line
Note: There can be a residual amount of voltage (up to 15V) detected between the neutral to line. This would still be deemed a dead circuit. It is good working practice to check all line terminals (permanent line, switched line, etc) for the presence of more than one power supply serving the installation.
STEP 11: RE-TEST THE EQUIPMENT
Once the test has been carried out, and the circuit is deemed to be dead, re-check the two-pole voltage indicator is still functional on the same proving system as Step 5 of the flow diagram in Appendix 1.
STEP 12: SAFE TO WORK ON APPLIANCE
Once all the above checks have been carried out, it should now be safe to carry out the work required. Always remain vigilant and re-check the circuit with the two-pole voltage indicator and proving device when moving away and returning to the appliance.
PROCESS FOR RE-ENERGISING THE CIRCUIT/SYSTEM
After completing the work, inspect and test to ensure that no damage has occurred. Remove the locking-off devices, locks and labels and restore the electrical supply. Once the supply has been re-energised, test the gas appliance for correct and safe operation (eg, 26/9 checks as per GSIUR). Complete and issue any appropriate documentation.
FURTHER INFORMATION AND GUIDANCE
It is important that the person carrying out the work is competent to undertake the task in hand. They should also be aware of any specific requirements that may be placed upon them by the type of environment they are working in, for example, there may be a need for a permit to work in certain circumstances.
Further guidance can be found at:
- hse.gov.uk/electricity/
- hse.gov.uk/pUbns/priced/gs38.pdf
- electricalsafetyfirst.org.uk/media/1201/Best-Practice-Guide-2-Issue-3-.pdf
Note: For general information about the process behind the development of Gas Safe Register Technical Bulletins and the expectations for all Stakeholders, see TB 1000(3) by logging into your online account at: www.GasSafeRegister.co.uk/sign-in
Bibliography
LNIDL – Gas Safe Register Legislative, Normative & Informative Document List
HSG85 – Electricity at work – Safe working practices (HSE Books)
TB 1000 – An introduction to Gas Safe Register Technical Bulletins
Appendix 1
The following flow chart should be followed to ensure safe isolation is achieved:
Appendix 2
An example of an electrical safety advice notice to be left with the responsible person:
ELECTRICAL SAFETY ADVICE NOTICE
FOR YOUR SAFETY: THIS IS NOT A CIRCULAR
Address:
Date:
To whom it may concern,
Whilst carrying out an electrical safe-to-touch check in accordance with Technical Bulletin 118a, an unexpected result was recorded. This may indicate that the gas appliance casing/installation pipework has electrical voltage present on the metallic parts and therefore I am/we are unable to work on your gas installation.
I/we would therefore recommend that you contact an electrically competent person to carry out further electric tests to ascertain if the electrical system at your property is safe for continued use and complies with current electrical requirements.
If your property is rented, please pass this information to your landlord/managing agent immediately.
If you should require advice on how to contact a local registered electrician, visit the Electrical Safety First website: www.electricalsafetyfirst.org.uk/find-an-electrician/ and visit the ‘Find an Electrician’ page.
I am/we are unable to proceed with any further gas safety tests/checks at your property at this time until an electrically competent person has tested and proved that your electrical system is safe for continued use.
Yours faithfully
PLEASE DO NOT IGNORE THIS ADVICE
IT IS FOR YOUR SAFETY
Appendix 3
Below is a useful checklist to help you ensure that all steps have been completed:
Step | Action required | Pass |
1 | Check with responsible person that it is acceptable to isolate the circuit/equipment | |
2 | Select an approved no-contact voltage detector. Check for damage and verify voltage detector on a known live source | |
3 | Carry out sweep check on appliance/gas meter and any associated pipework as per no-contact voltage detector manufacturer’s instructions. If no voltage is indicated, re-check the no-contact voltage detector on known live source | |
4 | Identify the point of electrical isolation for gas appliance that is to be worked on | |
5 | Select an approved two-pole voltage indicator. Check for damage and verify on known live source or proving unit | |
6 | Verify that the gas appliance is functional | |
7 | Identify suitable means of isolation for the gas appliance | |
8 | Isolate the gas appliance | |
9 | Fit appropriate lock-off device and locks to isolation point. Fit warning label for isolation and identified work | |
10 | Verify the gas appliance is isolated using two-pole voltage indictor | |
11 | Re-check the two-pole voltage indicator is functional as per Step 5 | |
12 | Gas appliance should now be safe to work on | |
After completing the work, inspect and test to ensure that no damage has occurred. Remove the locking-off devices, locks and labels, and restore the electrical supply. Once the supply has be re-energised, test the gas appliance for correct and safe operation (eg 26/9 checks as per GSIUR). Complete and issue any appropriate documentation. |