A consumer unit replacement is one of the more disruptive pieces of routine electrical work because the supply has to be isolated for most of the day. The first question most homeowners ask after agreeing to the work is exactly how long they will be without power. The honest answer for a typical Scottish residential installation is 4 to 8 hours of supply isolation, with the full work completed in a single working day. This guide walks through every stage of the timeline so you know what to expect from start to finish.
The headline timeline
For a typical 3 bedroom Aberdeenshire residential property with a 10 way consumer unit:
- Total work time on the day: 6 to 8 hours from arrival to handover.
- Supply isolation: 4 to 6 hours during the middle of the working day.
- Power restored to the property: typically by mid afternoon (15:00 to 16:00).
- Pre installation survey: separate visit, typically 30 to 60 minutes 1 to 3 weeks before the installation day.
- Lead time from booking to installation: 5 to 10 working days for standard residential bookings.
Larger or more complex installations take longer. Smaller flats with fewer circuits can be quicker. The figures above represent the most common scenario.
Stage by stage breakdown of the installation day
Here is what happens on the day, hour by hour, for a typical 3 bedroom Aberdeenshire property:
09:00 to 09:30: Arrival and setup
Faithful Spark arrives at the property and confirms the working area. The new consumer unit, all required protective devices, tools, and testing equipment are brought in. We confirm any specific requirements with the homeowner (where the temporary supply for fridge or freezer should connect, what time the family needs to leave for school or work, any pets that need to be kept clear of the work area).
09:30 to 10:00: Pre work checks
Before isolating the supply, we test each circuit to confirm correct identification (which circuit feeds which part of the property), check that no critical equipment is connected (no medical equipment, no important running computers), and prepare the new unit for installation. The supply is left on during this stage.
10:00 to 10:15: Isolation
The main switch is turned off and the supply tails are disconnected at the meter (or at the main switch on a slimline unit). The property is now without power. From this point, work proceeds as quickly as practical to minimise the duration of the outage.
10:15 to 11:00: Removal of the existing unit
The existing consumer unit is removed from the wall. Each circuit cable is identified and labelled at the cable end. The wall behind the existing unit is checked and prepared for the new unit (filling any small holes, cleaning surface dust, confirming a level mounting position).
11:00 to 12:30: New unit fitting
The new consumer unit is mounted on the wall. The main switch and protective devices (MCBs, RCDs, RCBOs) are positioned in the unit according to the design. Each circuit cable is connected to the appropriate protective device. Cables are dressed neatly inside the unit. The unit’s inspection cover is fitted.
12:30 to 13:00: Reconnection of supply
The supply tails are reconnected at the meter end. The main earth conductor is connected. The unit is closed and the main switch is turned on. The supply is now restored, but each individual circuit is still off pending testing.
13:00 to 14:30: Initial commissioning
Each MCB or RCBO is switched on individually, with a brief load test to confirm the circuit responds correctly. The RCDs are tested with the test button to confirm correct trip behaviour. Any issues identified at this stage are investigated and resolved before proceeding to formal testing.
14:30 to 16:00: Full electrical testing
Every circuit is now tested individually to BS 7671 standards. The tests include:
- Insulation resistance: measured between live conductors and earth at each circuit.
- Polarity: verified at each accessory on each circuit.
- Earth fault loop impedance: measured at the furthest point on each circuit.
- Earth continuity: measured between earth bar and accessory earths.
- RCD trip times: measured for each RCD or RCBO at multiple test currents.
Test results are recorded for the Electrical Installation Certificate. Any test result outside the expected range triggers further investigation. For most properties, all tests pass and certification proceeds.
16:00 to 16:30: Documentation and handover
The Electrical Installation Certificate is completed and printed (or emailed). The homeowner is shown the new unit, the location of each protective device, the location of the main switch, and how to reset a tripped breaker. Any questions are answered. The work is notified to Building Standards through the NICEIC competent person scheme.
16:30: Handover complete
The work is finished. The property has its new consumer unit, full supply restored, and the certification documents in hand. Faithful Spark is on call for any post installation questions.
What affects the duration?
Number of circuits
Each circuit takes time to identify, disconnect, reconnect, and test. A 6 way unit is faster than a 14 way unit. A flat with 4 circuits may be completed by lunchtime; a large detached home with 16 circuits may run to early evening.
Property size and layout
Testing each circuit requires measurements at the furthest accessory point. A larger property means more walking back and forth between the consumer unit and the accessories. Smaller flats are quicker to test than large multi storey houses.
Existing wiring condition
Where existing circuits show issues during testing (cables that have lost insulation, accessories that need replacement, junctions that need investigation), the time required to address these expands. Most issues identified are resolved on the day; significant remedial work may need to be scheduled for a follow up visit.
Type of consumer unit
A full RCBO board takes slightly longer to install and test than a split load unit because each circuit has its own RCBO that needs to be fitted, connected, and tested individually. The difference is typically 30 to 60 minutes.
Associated work
If the project includes additional work (an EV charger circuit, additional sockets, smoke detector wiring, earthing upgrades), the day extends to accommodate this. Typically a consumer unit replacement plus an EV charger circuit can still be completed in a single working day by 17:00 to 18:00.
What can the homeowner do during the supply outage?
The 4 to 6 hour supply outage covers most of the working day. Practical guidance for the homeowner:
- Plan to be out for the working day or to work elsewhere. The property will not have power for most of the productive hours.
- Keep fridge and freezer closed. A fridge maintains safe temperatures for 4 hours unopened; a freezer maintains for 24 hours. We can connect a temporary supply to the fridge or freezer where required.
- Charge phones, laptops, and other devices the night before. No charging is possible during the outage.
- Postpone household tasks that need power. Washing, cooking, and significant computer work all need power. Plan around the outage.
- Heating is generally fine during a single day outage. Gas central heating works without electricity (though the boiler controls and pump need power on most modern systems).
- Make sure pets have water and food before the work starts. Some pet equipment such as automatic feeders or aquarium pumps will not work during the outage.
Pre installation timeline: from booking to installation day
Before the installation day itself, several steps occur:
- Initial enquiry to survey: 1 to 7 working days from your enquiry to the survey appointment.
- Survey: 30 to 60 minutes at the property. Faithful Spark inspects the existing unit, counts circuits, identifies any associated work needed.
- Quote: 1 to 3 working days from survey to written quote.
- Quote acceptance: the homeowner reviews and accepts the quote.
- Installation booking: 5 to 10 working days from quote acceptance to installation day for standard residential bookings. Urgent bookings can usually be accommodated within 2 to 5 working days.
Total elapsed time from initial enquiry to completed installation: typically 2 to 4 weeks for a standard residential project, less for urgent bookings.
Frequently asked questions
Can the work be split across two days?
It is technically possible but rarely practical. The supply needs to be isolated to fit the new unit, then restored before the homeowner leaves the property unattended. Splitting the work across two days means two outages and two visits, which costs more in total than a single day completion.
What if I need to leave before the work is finished?
The homeowner does not need to be present for the entire day, but someone should be available at the start (to provide access and confirm the working area) and at the end (for the handover and certificate). Many homeowners attend the start, leave for work, and return mid afternoon. We coordinate this with the family schedule.
Can the supply outage be reduced for medical reasons?
Where a household member depends on mains powered medical equipment (oxygen concentrator, dialysis machine, sleep apnoea CPAP), please tell us at the survey stage. We can arrange a temporary supply for the affected equipment so it remains operational throughout the work.
What happens if testing reveals a problem mid afternoon?
Most issues identified during testing are resolved the same day. Common issues include a single accessory needing replacement (£30 to £60 added cost), or a junction needing repair (£80 to £150). Faithful Spark explains the issue, provides a quote, and addresses the work before completing the certificate where the homeowner agrees. Significant remedial work that cannot be done the same day is scheduled for a follow up visit.
Can the consumer unit replacement be done while I am away on holiday?
Yes, with appropriate access arrangements. Faithful Spark can carry out the work with a key holder or property manager providing access. We confirm the work is complete and send the Electrical Installation Certificate by email. This is a common arrangement for landlord properties between tenancies.
Book your consumer unit replacement
Faithful Spark provides NICEIC certified consumer unit replacements across Aberdeen, Aberdeenshire, Peterhead, Ellon, and Fraserburgh. Single day completion for most residential installations, fixed price quotes, and full certification at handover. See our pillar guides on consumer unit upgrades in Aberdeen and fuse box replacement costs in Scotland.
Book My Consumer Unit Replacement
Faithful Spark Electricians. NICEIC approved. Local Aberdeen team. Consumer unit upgrades, fuse box replacements, and Electrical Installation Certificates for Aberdeen, Peterhead, Ellon, Fraserburgh and across Aberdeenshire.
