safety isolator procedures are in place to ensure that workers on site are not exposed to danger when working on or near live electrical systems. There are many reports where these procedures have not been followed correctly and sadly this has resulted in needless loss of life.
One such report involves a large UK electrical contractor, where a circuit had been labelled as not in use, however the engineer working on the system did not have the necessary equipment to prove the system was dead. As a result he came into contact with a live conductor and was killed. The company in question was found guilty of failing to provide the right equipment and fined £300,000 by the HSE.
The Electrical Safety Council has produced a guidance document that covers the best practice for safe isolation and part of this guidance covers the test equipment that should be used. Using the right equipment is one of the most important parts of the procedure, as failure to do so can result in a circuit remaining live, resulting in injury or death.
What equipment is required for safe isolation?
The Electrical Safety Council Guidance states that “… The point of isolation should be locked off using a unique key or combination retained by the person carrying out the work or the appointed person, and a caution notice attached to the point of isolation.
Where more than one operative is working on circuits supplied from an isolated distribution board, a multi-lock hasp can be used to prevent operation… “
Locking off kits are available to ensure you have all the necessary equipment to lock out the circuit being worked on.
Once the breaker has been locked off correctly, a warning tag should be attached to clearly identify that the circuit has been locked off and is currently being worked on.
Locking off the circuit correctly is just one part of the procedure, before carrying out any work on the circuit, you should also verify that the circuit is definitely dead before proceeding, this is partly because circuits are frequently mis-labelled. In order to do this, you should use a dedicated voltage indicator and a proving unit.
The Electrical Safety Council Guidance makes a number of points in regard to use of voltage indicators to prove dead, some of the key ones are:
“Following isolation of equipment or circuits and before starting work it should be proved that the parts to work on, and those nearby, are dead.
It should never be assumed that equipment is dead because a particular isolation device has been placed in the OFF position.”
What is the correct equipment for proving dead?
As the Electrical Safety Council states, you should use a dedicated voltage indicator and a proving unit when carrying out this procedure. The list of suitable equipment includes test lamps, or a two-pole voltage indicator.
It is important to note that the voltage indicator MUST be able to work without the need for a battery, if you are using a device that needs a battery in order to work and the battery is flat, then you will not be able to prove if the circuit is dead or not!
Whilst you can use a known live source to test your voltage indicator, it is recommended that you use a dedicated proving unit.
Why can’t I use a Multimeter or non-contact voltage detector to prove dead?
Firstly, the use of Multimeters or non-contact voltage detectors is advised against in the HSE guidance and the use of these has resulted in accidents in the past.
The reason why a Multimeter is not suitable is due to the fact that it is all too easy to select the wrong range and in addition the Multimeter relies on battery power to function, thus there is a great margin for error in making a false “dead” reading on a live circuit.
Non-contact voltage detectors also require a battery in order to work, however they are typically sensitive to other signals, such as static electricity.
In conclusion, this article has briefly touched on safety isolator procedures, further information can be found on the HSE website and the full guidance note is available online.
The key point here is that whilst there is a cost involved in the purchase of new equipment, is it worth risking your life for the sake of a few pounds?