The need for isolation for electrical work
A health and safety briefing provided by the IET.
The main requirements for safe work on or near high energy electrical systems/sources usually require that every effort is made to securely isolate the source of energy, see: Safe maintenance of equipment (inc. machinery) and The manager's role in safe maintenance of equipment . This will be as a result of a risk assessment.
To help identify the precautions that are necessary for carrying out the work safely a risk assessment should be performed.