Live work justification on a 400 V board feeding critical refrigeration

Legislative test: under the Electrical Safety Act 2002 (Qld) and the Electrical Safety Regulation 2013, work on or near exposed live parts is only permitted where it is not reasonably practicable to de-energise, and only where a risk assessment shows the risk is adequately controlled. The question is not whether live work is possible - it is whether de-energising is reasonably practicable.

Here it plainly is:

• The shop is closed for 14 hours a day; the work can be scheduled after 6 pm or before opening.
• Refrigeration can hold temperature for a planned short outage, or a temporary chiller/generator can be arranged.
• The board has no internal shroud, so the busbars are exposed - this is not a controlled live-work environment.
• The fault itself (discoloured terminal, brittle insulation) suggests heat damage that may extend further than the MCB, requiring more work than twenty minutes.

So live work is not justified. The correct control is elimination: planned isolation.

Note that a live-work justification based on 'the owner says no' is not a risk assessment. Record the reasoning.

Apply the hierarchy in order, documenting each level.

1. Eliminate - always revisit isolation first: is there a downstream isolator, a removable link, a temporary supply, or a way to do the work at another time?
2. Substitute/engineering - fit temporary insulated barriers or shrouds over adjacent live parts, use IP2X shrouding, and work only on the section that must remain live.
3. Administrative - a documented risk assessment and a live-work permit signed by an authorised person; a written procedure; a second competent person present as safety observer, not doing the work; the area barricaded and signed; only the minimum number of people present; adequate lighting and a clear escape route; a rescue plan and first aid including CPR and defibrillator access.
4. PPE - arc-rated clothing and face protection appropriate to the calculated incident energy, voltage-rated insulated gloves (tested and within test date), insulated tools and matting, and a good-quality tester proven before and after use.

If any of these cannot be achieved, the work does not proceed. The correct outcome in this scenario is a scheduled shutdown.

Isolation and verification:

1. Notify the owner and anyone affected; agree the outage window and refrigeration arrangements.
2. Identify the correct isolation point and open the 250 A main isolator (and any upstream device if applicable).
3. Lock and tag the device with a personal lock, tag showing the reason, name and contact. Keep the key personally.
4. Prove the tester on a known live source or proving unit.
5. Test for dead at all conductors at the point of work - all phases, neutral and earth - proving phase-to-phase and phase-to-neutral as well as phase-to-earth.
6. Re-prove the tester after testing.
7. Where a neutral is to be disconnected, treat it as live until proven otherwise; watch for backfeeds from UPS, PV, generators or control circuits.
8. Fit a warning notice at the isolation point and confirm the working area is safe.

Before re-energising:

• Inspect and torque the new MCB and terminations to the manufacturer's specification; check the cable for heat damage and replace any affected length.
• Check the cause of the overheating (loose terminal, undersized cable, high ambient, harmonics) - the device alone may not be the root cause.
• Clear tools and debris, refit covers and shrouds, confirm no one is working on the circuit and that all locks are removed by the person who applied them.
• Re-test the affected circuit: insulation resistance, continuity, polarity, and functional check; verify with a clamp meter that the new MCB is not carrying more than its rating.
• Record the work and results, and advise the owner of any limitation you found.