Electric shock is not the only hazard. Where electrical arcing occurs, perhaps as a result of accidental short circuit, the heat generated can be intense and, even if it persists for only a very short time, it can cause deep-seated and slow-healing burns. Electricians often fail to appreciate the very real risk of injury that can arise from arcing. As a result, there are several hundred serious burn accidents each year arising from unsafe working practices. The intense ultraviolet radiation from an electric arc can also cause damage to the eyes.
Arcing, overheating and, in some cases, electrical leakage currents can cause fire or explosion by igniting flammable materials. This can cause death or injury and considerable financial loss.
Most electrical accidents occur because people are working on or near equipment that is:
Work on or near live conductors should rarely be permitted. Many accidents to electricians occur when they are working on equipment that could have been isolated. In most cases, adequate planning and work programming will allow such jobs to be carried out as the Regulations required, that is with the equipment dead.
Regulation 14 requires that three conditions are met for live working to be permitted where danger may arise. It is stressed that if just one of those conditions cannot be met, live working cannot be permitted and dead working is necessary.
The conditions are:
Five Important Factors to Consider Are:
Ensure Correct Methods
Before working on equipment made dead, the conductors should be proved dead. The instrument to do this should be properly constructed to protect against electric shock, and designed to prevent short circuits occurring during use. Adequate insulation and fusing or energy limitation are essential. Proprietary voltage detectors should be used. It is necessary to test the instrument before and after use. This may be done by means of a proving unit with a low power output. However, if live circuits are used to prove instruments, adequate precautions against electric shock and short circuits should be taken.
Notices or labels should be placed at the point of disconnection so everyone else knows that work is being done. A good system is to use a ‘caution’ notice to indicate that someone is working on the apparatus and may be injured if it is re-energised. This should be supplemented by ‘danger’ notices adjacent to the place of work indicating nearby apparatus that is still energised. Notices or labels should be easily understandable to anyone in the area. It is also important to remove labels or notices when they no longer apply, so that the system does not fall into disrepute.
To ensure adequate isolation, the disconnecting device should have an isolating gap sufficient for the voltage levels present or likely to occur. Make sure that any switch disconnector or other means of disconnection is secure. Switches should preferably to locked in the OFF position using a ‘safety’ lock, ie a lock with a unique key. If a plug has been withdrawn, make sure that it cannot be reconnected to the electrical supply while work is taking place on the circuits or apparatus. If a fuse is removed, make sure that it or a similar one cannot be reinserted by taking it away or by locking the box or enclosure until work is completed.
Having isolated the circuit or equipment, check at the point of work that the parts to be worked on or near really are dead, as there may be a back up supply. If it is a three-phase system or equipment with more than one supply, prove that all supply conductors are dead. The device used for proving dead should itself be proved immediately before and after testing.