All electrical installations must be isolated and proven dead before work can commence. Securely “disconnecting” (isolating) one or all parts of the installation from the live supply is called `Safe Isolation`. There can be several ways of isolating an installation. Most common is by means of a Main Switch. If there is a need to isolate only one circuit at the time, then an MCB provides isolation. In domestic environment it is usually the main fuse that gets removed.
There are industry-wide recommendations on correct procedures in order to achieve safe isolation. The steps described bellow form the Safe Isolation procedure. Before starting the Safe Isolation Procedure, remember to seek permission from a relevant responsible person, beacause there might be certain vital services that must not be interrupted at any time. There might be a permit to work system in place to which you will need to comply.
Step 1. Identify the point of isolation for the system or circuit. Lock off, place warning label and keep the key to the lock with yourself.
Step 2. Select the correct and mains approved test equipment and ensure that it works correctly by testing on the proving unit.
Step 3. Test the outgoing side of the means of isolation (Main Switch, MCB, Fuse, etc.) to make sure it is dead. Depending on the type of the supply you will need to complete the following tests:
Single Phase installations test to confirm that there is no voltage between:
3 Phase installations test to confirm that there is no voltage between:
Step 4. Re-test the test equipment on the proving unit.