19.2 Commissioning & Decommissioning

Commissioning & Decommissioning

Quick Answer: Commissioning is the controlled process of bringing a verified installation into service: energise, check circuit voltages, check phase rotation and polarity, load up systematically, confirm the installation functions correctly and check instrument and control parameters. Decommissioning is the reverse discipline: identify every circuit, assess the impact on other equipment, isolate, tag, test, secure and earth where required, then safely remove or terminate unused cable.

A Systems Approach

"Systems approach" is the phrase in the capability, and it is the whole point. You are not switching on a light; you are bringing a system into service in a controlled sequence where each step confirms the previous one before adding energy or load.

The three phases:

1. Verification (Chapter 15) — proving the installation is safe to connect.
2. Commissioning — bringing it into service in stages and confirming it behaves as designed.
3. Handover — documentation, certificates, schedules, as-installed drawings and operator instruction.

Commissioning never substitutes for verification. If Section 8 testing has not passed, there is nothing to commission.

The Commissioning Sequence

1. Pre-energisation confirmation

• Verification tests complete and results recorded.
• All covers, escutcheons and barriers fitted; no exposed live parts.
• All circuits labelled and the board schedule complete.
• Personnel notified and the area controlled — nobody working downstream.
• Distributor or supply authority requirements satisfied where connection depends on them.

2. Circuit voltage testing

Energise progressively and confirm at each board:

• Line to neutral on each phase — expect approximately 230 V.
• Line to line — expect approximately 400 V.
• Line to earth, confirming the earthing reference is present.
• Unequal or missing voltages point to a lost phase, a loose connection or a wrongly landed conductor. Investigate before proceeding; do not "load it and see".

3. Phase rotation and polarity checks

• Confirm rotation with an indicator at each board and at every point feeding rotating plant (Section 16.3).
• Confirm polarity at outlets and equipment — active to active, neutral to neutral, earth to earth.
• Confirm rotation is consistent across boards, not merely correct at one.

4. Systematic loading up

Do not close every device at once. Load the installation in stages:

1. Energise the main switchboard and confirm.
2. Energise each submain and confirm at the distribution board.
3. Energise circuits group by group, confirming current and voltage as load is added.
4. Start rotating plant individually, observing starting current and confirming direction before coupling where practicable.
5. Watch for voltage dip, unexpected tripping, unbalanced loading and unusual noise or smell at each stage.

Staged loading is what allows you to attribute a problem to the step that caused it. Energising everything simultaneously turns a five-minute diagnosis into a half-day.

5. Correct installation functioning

• Confirm each circuit does what its label says.
• Confirm switching, control, emergency stops and interlocks operate as designed.
• Confirm RCDs trip on test and on the instrument, and that they reset.
• Confirm lighting control, time clocks and sensors behave as specified.

6. Instrument and control parameter checks

• Set and record overload relay settings, trip classes, drive parameters and protection settings.
• Confirm metering reads correctly and CT ratios match the meter configuration.
• Record every setpoint — an undocumented setting is one nobody can restore after a fault.

7. Dangers of mechanical damage

Throughout commissioning, watch for cables and equipment damaged by other trades: plasterers, tilers and ceiling fixers regularly damage cables after the electrician's rough-in. Re-inspect accessible routes before final energisation.

The Decommissioning Sequence

Decommissioning is where an unhurried electrician stays safe and a rushed one energises a conductor they thought was dead.

1. Identification of all circuits

Establish exactly what is being removed and everything it feeds. Use drawings, schedules and physical tracing. Assume records are incomplete until proved otherwise.

2. Impact on other equipment

Ask what else depends on this supply: shared neutrals, control interlocks, fire and security systems, emergency lighting, refrigeration, IT equipment on the same board. Removing a circuit that shares a neutral with a live circuit is a shock hazard and a functional failure.

3. Isolation

Isolate all sources, including any secondary or backup supply — generators, UPS, solar inverters and battery systems. Apply the full identify–isolate–lock–tag–prove sequence from Chapter 14.

4. Tagging

Tag at the point of isolation with who applied it, when and why. Personal locks stay with the person who applied them.

5. Testing

Prove dead at the point of work with a proving unit before and after. On a decommissioning job the conductor you are about to cut is the one that must be proved.

6. Securing and earthing where required

For high-energy or high-voltage systems, apply earths as the procedure requires so induced or stored energy cannot re-energise the conductor. Capacitor banks and drive DC buses must be discharged and confirmed.

7. Safe removal and termination of unused cable

• Withdraw the cable completely where practicable.
• Where a cable cannot be withdrawn, disconnect it at the source, terminate the conductors safely in an accessible enclosure, and label it clearly as disconnected and dead.
• Never leave an unterminated conductor that could be re-energised. An abandoned live conductor in a ceiling space is a serious defect and has killed people.
• Update drawings and the board schedule, and remove the redundant circuit label so nobody thinks it still exists.