Electrical installation in a two-bedroom flat: first fix and second fix

The job happens in two stages, with several weeks of other trades in between. The first fix is the rough-in. The electricians cut chases and holes for back boxes, lay the cables and set the boxes and the consumer unit. They also connect the supply cable from the meter cupboard in the corridor. After that come the plasterers, tilers and decorators. The second fix is the finishing stage. The electricians fit sockets, switches and lighting points, install the breakers and RCDs in the consumer unit, then power up the circuits and test them.

A typical two-bedroom flat has a living room, often open to the kitchen, plus a bedroom, a bathroom, a separate or combined toilet, a hallway and sometimes a balcony. The two bedrooms are often one main bedroom and a smaller room that serves as a study or a child's room. Altogether that usually means several dozen points: sockets, switches, ceiling and wall lighting outlets, and dedicated supplies for appliances. The consumer unit usually ends up with roughly 12 to 18 circuits. The exact number depends mostly on how the kitchen is equipped and whether hot water comes from an electric water heater.

Before you sign anything, check what exactly the package includes. Three things cause the most confusion. Is the initial inspection and testing, with a written certificate or report, included? Who buys the sockets and switches? A basic range and a designer series are very different things. And does the price cover removing the old wiring and filling the chases afterwards? Some electricians fill the chases with plaster themselves, others leave it to the plasterer.

Site visit and layout

A good electrician first walks through the flat with you and marks the walls with chalk or a marker. Where will the bed go, the sofa, the TV, the desk, the kitchen units? They also check the incoming supply from the corridor: the rating of the main breaker, whether it is single-phase or three-phase, and what conductors run in the riser. From this they draw up a simple circuit plan and a consumer unit layout. A two-bedroom flat rarely needs a full design project, but a clear drawing of every point saves a lot of arguments later.

Removing the old installation

In older panel blocks the original aluminium wiring often runs through hollow cores in the ceiling slabs or in chases that are hard to trace. Usually the old cables are disconnected and left dead in the wall, and the new wiring takes a different route. What matters is that nothing forgotten stays live after the strip-out. That is why everything is disconnected at the consumer unit first and clearly labelled.

Chasing walls and setting boxes

Chases are cut with a wall chaser connected to a dust extractor, and box holes are drilled with a core bit. In hard panel concrete this is slow and loud work, in brick it is much quicker. Chases should follow the standard installation zones. Horizontal runs usually sit roughly 30 cm below the ceiling or above the floor, vertical runs roughly 10 to 20 cm from corners, door frames and window reveals. Ten years later, anyone hanging a shelf can then guess where not to drill. Deep or long horizontal chases must not be cut into load-bearing panels, because that weakens the structure.

Pulling cables and fitting the consumer unit

Cables go into the chases, sometimes inside flexible conduit, and are fixed with plaster dabs or clips. A loop of spare cable is left at every box so the connections can be made comfortably. A new consumer unit goes in the hallway, usually recessed into the wall. The supply cable from the meter cupboard is often replaced as well, because the original is typically aluminium and too small for modern loads.

Second fix, commissioning and testing

Once the walls are plastered, tiled and painted, the electricians come back. They fit the accessories, wire up the consumer unit, label every circuit and power them up one by one. Then comes the initial inspection and testing. A qualified tester measures insulation resistance, earth fault loop impedance and continuity of the protective conductors, and checks that each RCD trips as it should. You receive a written certificate or test report. Keep it safe. Insurers often ask for it after a claim, buyers want to see it when you sell, and the network operator may ask for it when you change the main breaker.

How long it takes

For a two-person crew, the first fix in a two-bedroom flat usually takes about 4 to 7 working days, at the longer end in panel concrete. Second fix and testing typically take 1 to 2 days. Between the two stages you wait for the chases to be filled, the plastering, tiling and painting. Plaster in the chases dries in roughly a day to a few days depending on depth, while new plaster on whole walls takes considerably longer.

Decisions that are hard to change later

• Kitchen design. Without a drawing of the units, the electrician cannot know where the oven, hob, dishwasher, fridge and cooker hood will go. A hob usually needs its own supply, often three-phase. Worktop sockets have to land between wall cabinets, not behind them.
• Furniture layout in both bedrooms. If the second bedroom will be a home office or a child's room, it needs more sockets and different switch positions than a guest room.
• Bathroom. Where the washing machine, water heater, illuminated mirror and any electric underfloor heating or towel rail will go.
• Data and TV. If you want wired internet in the bedroom or behind the TV, conduits for data are laid at the same time as the power cables.
• Lighting. Downlights in a plasterboard ceiling, LED strips, two-way switching in the hallway. All of this has to be decided before the cables go in.

Building management, the building authority and neighbours

Tell the building management or owners' association before you start. The meter cupboard in the corridor and the riser belong to the common parts of the building or to the network operator, so any work on them has to be agreed in advance. If you want a higher main breaker rating or a switch to three-phase supply, you need the approval of the local network operator and often the consent of the management as well.

Replacing the wiring inside a flat without touching load-bearing structures is usually treated as minor work, but local building regulations differ. Check with your local building authority whether anything needs to be notified, especially if you are also removing partition walls or changing the layout. If you have any doubt about chases in load-bearing walls, ask a structural engineer. Respect the house rules on when noisy work is allowed, and give your neighbours a few days' notice before the chasing starts.

Gas in the flat

If the flat has a gas cooker or boiler, the electricians must know exactly where the gas pipe runs. If you smell gas during the work, do not switch anything on or off. Open the windows, leave the flat and call the gas emergency number or 112.

Cables

New installations use copper conductors only. Lighting circuits typically use 1.5 mm² cable, socket circuits 2.5 mm², and a hob usually a five-core 2.5 mm² cable, or heavier depending on its rating and the manufacturer's instructions. Joining new copper and old aluminium in the same terminal is a bad idea. The joint loosens over time, heats up and can start a fire. If any part of the old installation stays, it is connected only with special terminals rated for both aluminium and copper.

Protection in the consumer unit

• RCD with a 30 mA trip rating protects people against electric shock. Under the wiring rules, socket circuits and bathrooms should always have one.
• RCBOs, which combine an RCD and a breaker for each circuit. If the washing machine develops a fault, only its circuit switches off, not the whole flat. They take more space and cost more, but in a two-bedroom flat they are worth it at least for the kitchen and bathroom.
• Surge protection guards electronics against voltage spikes from the network. How much sense it makes depends on the protection already installed in the building, so ask your electrician.

Boxes and accessories

Standard flush back boxes go into concrete and brick, and special cavity boxes with clamps go into plasterboard. If you want double or triple sockets next to or above each other, the boxes must be drilled at exact spacing, otherwise the multi-frame will not fit. Switches and sockets differ mainly in looks and in how long the mechanism lasts. A cheap switch starts to feel stiff after a few years, a good one lasts decades.

Smart home

If you are thinking about smart control of lighting or blinds, decide before the first fix. Some systems need deeper boxes or a neutral conductor at the switch. Adding a neutral later means chasing the walls again.

The NUMIQ price list has separate rewiring packages by number of rooms. The difference is not just floor area. The number of circuits, the size of the consumer unit and the time on site all change.

• One-room flat: a single living space, often with the kitchen in it, and fewer circuits. The consumer unit is smaller and the work is quicker. This package also suits studios.
• Two-bedroom flat, the subject of this page, adds a separate bedroom and almost always a separate or larger kitchen. The main tasks here are splitting circuits sensibly between the living and kitchen area and the bedroom, two-way switching in the hallway, and enough sockets for a home office.
• Three-bedroom flat has another room, a longer hallway and often a separate toilet and bathroom. There are noticeably more circuits, the consumer unit needs an extra row, and the work takes longer.
• Four and five-room flats are more common in new builds or large city apartments. They often involve several bathrooms, three-phase supply, underfloor heating and a more detailed design.

What makes a two-bedroom flat interesting is that almost everything a large flat has meets in a small space: a full kitchen, a bathroom with a washing machine, a work spot and a bedroom. Meanwhile the consumer unit has to fit into a narrow hallway, often between the front door and a built-in wardrobe. It needs to stay reachable even when the wardrobe is full. If your flat has a large living room split into two zones, or you plan to divide off another room with a partition, talk to your electrician. In scope you may be closer to the three-bedroom package.

Easier

• An empty flat with no furniture, old tiles knocked off and floors removed
• Brick or plasterboard partitions where chases are quick to cut
• A finished kitchen design and a clear furniture layout
• Access to the meter cupboard and agreement with the building management in advance

Harder

• Hard concrete panel walls where the chaser moves slowly and blades wear quickly
• Rewiring a lived-in flat, where furniture has to be moved and everything covered against dust
• Layout changes during the job, which mean new chases in walls already made good
• An outdated supply in the riser that has to be sorted out with the building and the network operator
• Suspended ceilings, downlights and LED strips, which add points and time

Coordinating with other trades

The electrician comes after the strip-out and usually works alongside the plumber running water and waste pipes. The two need to agree on routes so cables do not cross pipes and the washing machine socket does not end up right next to the waste outlet. Then come filling the chases, plastering, plasterboard, tiling and painting. Second fix happens only after painting, otherwise the accessories get spattered. When tiling, make sure the tiler cuts neat openings around the boxes and that the boxes do not end up sunk too deep behind the tiles.

• Too few sockets. In practice it often happens that a year later the living room is full of extension leads. Plan more sockets by the TV and the desk than you think you need today.
• Everything on one circuit. A kettle, microwave and oven on the same breaker mean trips while you cook.
• Chases outside the zones. Diagonal or random cable runs show up years later as a drilled-through cable when someone hangs a shelf.
• Missing supplementary bonding in the bathroom. You cannot see it, but if an appliance fails it is a safety risk. The tester has to check it where the rules require it.
• An unlabelled consumer unit. When something trips, nobody knows which breaker does what. Every circuit needs a clear label.
• Loose connections in boxes. Poorly tightened terminals heat up. You notice flickering lights, a burning smell or a discoloured socket.
• Second fix before painting. Paint on switches and frames does not come off properly, so they have to be replaced.

A flat installation may only be installed and connected by a qualified electrician, and tested by someone qualified to do so. For that reason this article has no DIY instructions. You can help by carrying out rubble, protecting floors and cleaning up, but leave all work on the wiring to professionals.

Take your time at handover and go through the flat room by room with the electrician. Switch on every light, plug a simple appliance or socket tester into every socket and press the test button on each RCD.

• The test certificate or report has been handed over, signed and without serious defects
• Every breaker and RCD in the consumer unit is clearly labelled
• A circuit chart is kept in the flat, ideally with a sketch of the cable routes
• All sockets are live and sit straight, with no gaps under the frames
• Switches control the right lights and two-way switching works in the hallway
• RCDs trip when the test button is pressed
• Supplies for the oven, hob, dishwasher and washing machine are where the kitchen design shows them
• The bathroom has bonding where required and sockets are outside the zones around the bath and shower
• No loose conductor has been left anywhere without a cover or terminal
• The flat has been cleaned and rubble removed as agreed