Health & safety bulletin
Electrical work
29th April 2005
Electrical work is dangerous, around 1000 electrical accidents at work are reported to HSE each year and about 30 people die of their injuries.
Engineers should never work on any electrical equipment unless it is turned off. Live working is illegal except in very specific circumstances that would never apply to the sign industry.
In some cases in the sign industry it can be unclear where the boundary lies between the sign fitters and the electrician’s responsibilities. Some clients have tried to define this, by stating that no electrical work is to be carried out by sign fitters and others simply insist on work only being carried out by a competent person. Where no such definition is imposed it has been down to individuals and historic practice to define the boundary, sometimes this is the transformer, sometimes a fireman’s switch, other times a local junction box. Wherever is chosen, this position should be defined at the planning stage and responsibility for circuit design, loading, connecting and testing specified. The location chosen should be as close to the sign as possible, the choice of a fireman’s switch as the boundary should only be adopted if it is local to the sign (within a couple of meters) and only switches the sign.
IF IN DOUBT, THE WORK SHOULD NOT BE UNDERTAKEN AND A SUPERVISOR OR MANAGER SHOULD BE CONSULTED.
Earthing / Bonding
All illuminated signs must be suitably earthed. If the sign enclosure is metal, this should be bonded.
Earthing and Bonding is required to ensure that in the event of a fault causing the metalwork to become live, then the fuse or circuit breaker will trip. If the metalwork is not adequately earthed, then the enclosure can remain live without detection indefinitely. If a maintenance worker or member of the public touches the metalwork, they would then receive a potentially lethal shock.
Water build-up
Water (and ice) is conductive, if a build-up of water occurs near live parts this can cause short circuit or earth faults. Always ensure that signs and enclosures are powered down before opening and that any electrical gear is kept dry. If water is building up in a sign, it must be reported to a supervisor. If drainage holes are present engineers must ensure that they are clear.
Capacitors
It is common to find capacitors in illuminated signs, especially in fluorescent lighting. Capacitors store an electrical charge and can remain dangerous even when the power is turned off. Engineers should never touch the terminals of a capacitor unless it has been safely discharged by a suitable method. the terminals of a charged capacitor should never be connected together as this will cause a short circuit that could potentially be dangerous and could damage the capacitor.
Safe Isolation
In order to ensure equipment being worked on is turned off, and that it cannot be turned back on until the work is finished, there is a standard Isolation Procedure that must be adopted.
- Locate the means of isolation. This should be labelled, however in most cases it would be the circuit breaker at the distribution board. The means of isolation must be able to be locked in the off position.
- Switch off the isolator. Ensure you have permission to do so beforehand.
- Lock the isolator in the off position. Take the keys to the lock with you. If the isolation device is a fuse, take the fuse with you.
- Using a suitable test meter, check the meter on a known supply or proving unit to ensure it is working.
- Test the circuit that has been isolated to ensure it is dead. Check between Live to Earth, Live to Neutral and Neutral to Earth to ensure a wring fault has not occurred.
- Using the same test meter, recheck to ensure the meter is still working.
- The equipment can now be worked on. Ensure the supply is re-energised after working on the equipment.
RCD
RCDs are seen by some as a magic device that will cure all sins. This is not so, RCDs only protect from earth faults, they will not protect against short circuits. If a sign is not earthed it is still possible for it to become live and remain so even if protected by an RCD.
RCDs function by detecting the difference in currents through the live and neutral conductors. During a short circuit the currents increase dramatically but remain correlated in both conductors, so the RCD will not trip.
RCDs come in several ratings; the only ones considered safe for direct contact with a live part are 10mA and 30mA devices. 10mA devices are rare. A lot of newer distribution boards come with RCDs built in; sometimes these are 30mA, however commonly they are 100mA devices. A 100mA device is not sufficient to prevent a dangerous shock – it may not kill but will cause muscle contractions that could result in secondary injuries, e.g. falling from height.
Do not be fooled into thinking it is safe to work on a sign live because it is protected by an RCD.
Conductor Colours
The colour of non-flexible cable conductors are in the process of being changed. The previous standard of using Red as live and Black as neutral is being phased out, with the colours of Brown as live and Blue as Neutral being introduced (the same colours as currently used in flexible cables). Existing installations will not have to be altered to suit the new colours, however you will start to see the new colours on new installations. All new installations after 31 March 2006 will have to use the new colour identification.
The colour of the earth remains unchanged at green/yellow.
Electrically Competent Persons
Please note that we are developing an electrical competency course “in house”, utilising the skills of our specialists who are qualified to Comp’Ex 7/8, IEE 16th Edition and C&G 2391 standards. The content and means of testing competency are currently being independently assessed.
If in doubt, never carry out any electrical work – ask for assistance, regardless of cost!!