School Refurbishment: Late Distribution Board and Phase Swapping
A secondary school is being refurbished over six weeks during term time. The work is split into four phases, each isolating one wing. Phase 2 is the IT suite and science labs; Phase 3 is the sports hall. The new distribution board for Phase 2 is delayed by 10 days. The main contractor wants to swap Phase 2 and Phase 3 to keep the programme on track. However, Phase 3 requires a new 200 A submain that has not yet been installed, and the sports hall is currently fed from the same board as Phase 2. The school insists that the IT suite and science labs must remain powered during school hours. You have two teams of three electricians. A temporary 63 A three-phase supply is available from a nearby plant room, 40 m away. The client wants a decision today.
1. Assess the proposal to swap Phase 2 and Phase 3. What are the key technical and programme risks, and what information would you need before agreeing?
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Swapping the phases is not a simple programme change. Phase 3 depends on a new 200 A submain that has not been installed, so bringing it forward would create a new critical path and may not be achievable in the time available. The sports hall is currently fed from the same board as Phase 2, which means the isolation boundaries are not independent; isolating one area may affect the other. The IT suite and science labs have specific power quality and availability needs, and the school requires them to remain live during school hours. Before agreeing, I would need the existing board schedules, the proposed new submain route and capacity, the load profile of the IT suite and labs, the school’s agreed shutdown windows, and the contract programme showing dependencies. I would also check whether the delayed board is on the contractor’s or client’s risk. Swapping phases without this information could compromise safety and create further delay.
2. If a temporary supply is used to maintain power to the IT suite and science labs, outline the key design checks and protection requirements for the 40 m run.
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The temporary supply must be treated as a designed installation, not an extension lead. First, calculate the connected load of the IT suite and science labs; for example, 10 kW and 15 kW respectively gives about 25 kW, or 36 A per phase at 400 V, so a 63 A three-phase supply is adequate but not generous. Select a 5-core SWA cable suitable for the 40 m run and check voltage drop; a 16 mm² cable at 36 A would give roughly 0.9% drop, which is acceptable. Confirm the protective device rating and type, and check the earth fault loop impedance and disconnection time. Provide 30 mA RCD protection for socket-outlet circuits and ensure the temporary distribution board is IP-rated for its location. The cable route must be protected against mechanical damage and clearly labelled as temporary. The supply must be isolated and locked off when work is complete, and the temporary arrangement should be recorded and removed at the end of the phase.
3. Explain how you would communicate the delay and any revised plan to the client and main contractor, including the contractual and safety implications.
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I would issue an early warning notice as soon as the 10-day delay is confirmed, setting out the cause, the affected activities, and the likely effect on the programme. I would not agree to a phase swap or a temporary supply without a written method statement and a clear allocation of risk. In a meeting with the client and main contractor, I would explain that the safety of the school users and the integrity of the installation take priority over programme pressure. I would propose a revised sequence that protects the IT suite and labs, such as installing the temporary supply while keeping Phase 2 live, and then progressing Phase 3 once the submain is available. Any additional cost or time would be recorded as a variation or compensation event under the contract. The conversation would be documented, and no work would proceed until the revised plan is agreed and the temporary arrangements are designed and checked.