Installation and Maintenance Practices
This domain covers how work is planned, executed and kept serviceable: method statements, coordination with other trades, correct termination, preventive and condition-based maintenance, and the records that prove the work was done. Answers that consider safe systems of work and evidence score better than pure technique.
Planning and control of the work
- A risk assessment and method statement, plus a permit to work where the task involves hot work, confined spaces or high-voltage switching; an isolation schedule and an agreed sequence with other trades.
- Access equipment inspected and recorded, with temporary supplies and lock-off arrangements agreed before first fix begins.
- Materials checked on delivery: cable drums for damage and length, accessory IP rating against the location, and temperature ratings against the load.
Termination and workmanship
- Strip to the correct length, avoid nicking strands, and use ferrules on fine-stranded conductors in spring terminals.
- Tighten to the manufacturer's torque with a calibrated wrench, and re-torque large lugs after thermal cycling.
- Support cables at the intervals given in BS 7671 Table 4A2, typically 300 to 400 mm for sheathed cable, and seal fire compartment penetrations.
- Label both ends of every core and record circuit identification on the board schedule.
Maintenance strategies
Reactive, time-based preventive and condition-based maintenance each have a place. Condition-based work uses thermography, trending insulation resistance, vibration and oil analysis, plus RCD trip-time checks at an interval set by the client's risk assessment. Always capture as-found readings, because they show deterioration and justify the intervention.
Worked example
A thermographic survey of a 400 A board shows one phase terminal 32 K above its sisters at 70 per cent load. Isolate and prove dead, clean the contact faces, re-terminate with a calibrated wrench to the manufacturer's 45 N m, then verify with a micro-ohmmeter that contact resistance matches the other phases, and re-scan under load. Record as-found and as-left temperatures with the load current, because a temperature delta without the corresponding load tells the next person nothing.
Traps that cost marks
- Working live to avoid downtime without documented justification and authorisation.
- Over-torquing, which crushes strands, raises resistance and creates the hotspot you were sent to cure.
- Accepting tape or a connector block as a permanent repair inside an enclosure.
- Reporting temperatures without the load current that produced them.