Here for reference is the safe isolation procedure taken from the new AM2 guide.
Safe Isolation for Dead Working
All LV installations must be isolated and proven dead before work can commence, except in case when dead working is unreasonable. Don`t forget that electricity kills, so it is vital that everyone in the electrical industry adopts safe working practices.
Safe isolation sequence:
• Seek permission from a relevant responsible person to isolate supply.
• Select the correct and mains approved test equipment and ensure it works correctly by testing on the proving unit.
• Identify the point of isolation for the system or circuit. Lock off, place warning label and keep the key to the lock with yourself.
• Test circuit to make sure it is dead.
• Re-test the test equipment on the proving unit.
• Begin work
Testing Single Phase Installation:
Test for voltage between the following:
• Phase and Neutral
• Phase and Earth
• Neutral and Earth
Testing 3 Phase four wire systems:
Test for voltage between the following:
• L1 and L2
• L1 and L3
• L1 and Neutral
• L1 and Earth
• L2 and L3
• L2 and Neutral
• L2 and Earth
• L3 and Neutral
• L3 and Earth
• Neutral and Earth
Remember:
When isolating the main source of energy it is also essential to isolate any secondary sources such as standby generators, uninterruptible power supplies (UPS) and microgenerators.