Electrical installation in a 4-room flat: first fix and second fix

Electricians split the job into two stages. The first is the first fix, the rough installation. It covers marking out cable routes, cutting chases into the walls, setting back boxes, pulling in cables and fixing the enclosure for the distribution board. Then the plasterers, drywall fitters, tilers and decorators take over. The second stage is the second fix. The electrician fits sockets and switches into the boxes, wires up the distribution board, connects fixed appliances and tests every circuit. Inspection and testing follow, and the result is a test certificate or inspection report.

A 4-room flat usually has a living room, three rooms (main bedroom, child's room, study or guest room), a kitchen, an entrance hall, a corridor and a bathroom, often with a separate WC or a second bathroom. Each of these rooms has different needs, so make clear at the start exactly what the quote covers. The package normally includes:

• Power and lighting circuits in all rooms
• Dedicated supplies for the hob, oven, dishwasher, washing machine and water heater
• A new distribution board (consumer unit) with circuit breakers, residual current devices (RCDs) and usually surge protection
• Supplementary bonding in the bathroom (metal water and waste pipes, and the bath if it is metal)
• Fitting switches and sockets and connecting light fittings to the ceiling and wall points
• Testing the installation and issuing the certificate

Several items are often unclear. These include supplying the light fittings themselves and low-voltage work (data points, TV cabling, doorbell or video entry). Two more are the supply cable from the meter in the stairwell to the flat and making good the chases afterwards. Ask about each one directly, because this is where most misunderstandings between customer and contractor start.

The price list has separate items for 1-room, 2-room, 3-room, 4-room and 5-room flats. The difference is not just metres of cable. With every extra room you get more circuits, a larger distribution board, more planning and more time for each stage. In simple terms:

• 1-room flat: one small board, a handful of circuits, often a single-phase supply, kitchen and living space in one room. The work takes a few days
• 2-room flat: a bedroom is added, socket circuits start being split by room, and the kitchen is usually separate
• 3-room flat: the most common family flat, where a three-phase supply and separate RCDs for groups of circuits start to make sense
• 4-room flat: three rooms plus a living room, often two wet rooms, a larger kitchen and a longer corridor. The board usually needs three or four rows of modules, there are noticeably more circuits, and with an induction hob and several large appliances a three-phase supply is almost always worthwhile where the network offers it
• 5-room flat: typically a maisonette or a large flat in an older brick building, with cable runs between floors, more two-way staircase lighting and sometimes two sub-distribution boards

What is specific to a 4-room flat

The first issue is load sharing. A family of four or five may run the washing machine, tumble dryer, dishwasher, hob, oven, several computers and, in summer, air conditioning all at once. In a smaller flat a sensible split of circuits is enough. Here the appliances have to be spread across the phases so the main breaker does not trip. When planning, the electrician should be able to tell you which appliance goes on which phase.

The second issue is how the RCDs are split. If the whole flat sits behind one RCD, a single damp socket on the balcony cuts power to everything, including the fridge and freezer. In a 4-room flat the circuits are usually divided into several groups, each with its own RCD. Sensitive circuits can also get combined breakers with built-in RCD protection (RCBOs).

The third issue is cable length. A bedroom at the end of the corridor can be quite far from a board in the entrance hall. On long runs with higher loads the electrician checks voltage drop and chooses the cable size to suit. In a small flat this rarely matters. Here it is a normal part of the design.

Changes during the job cost the most money and the most stress. Once a chase is cut and a cable pulled, moving a socket by a metre means more cutting and more making good. Before the crew starts, you should have the following settled.

Furniture and appliance layout

Draw every room with the beds, table, TV, wardrobes and kitchen units. For the kitchen, the ideal is the kitchen supplier's drawing with exact positions of appliances, the cooker hood and under-cabinet lighting. In the rooms, think about sockets on both sides of the bed, at the desk, behind the TV and where the router will go. People often ask how many sockets are enough. In practice people regret having too few far more often than too many, especially in the child's room and the study.

Building management, the building authority and the network operator

In a block of flats, always contact the building management or owners' association. Their main concerns are work on common parts, such as the supply cable from the meter in the stairwell and openings through floors and load-bearing walls. They also set the hours when noisy work is allowed under the house rules. Whether your renovation needs a notification, a permit or nothing depends on local building regulations and on the scope of work. It matters most whether you change the layout or touch load-bearing structures. Do not assume that nothing is needed. Check with your local building authority in advance. In many countries electrical work in a home must also be carried out or certified by a qualified electrician.

If you plan to increase the main fuse rating or move from a single-phase to a three-phase supply, you apply to the local network operator. This can take several weeks, so it is wise to start before the renovation itself.

Site readiness

• Old plaster, tiles and ceilings removed wherever they are being replaced
• A clear decision on plasterboard ceilings or wall linings, because cables run differently in them than in masonry
• The finished floor level marked, since box heights are measured from it
• A temporary power supply for tools if the old installation is disconnected all at once

Survey, design and marking out

The electrician inspects the flat and checks the incoming supply, the condition of the meter cupboard in the stairwell and what the walls are made of. Then you walk through the flat room by room together, and the electrician marks boxes and routes directly on the walls. This is the most important hour of the whole job. If you can, be there in person and bring your furniture measurements.

Removing the old installation

In a renovated flat, old aluminium conductors are usually pulled out or disconnected and abandoned. Aluminium becomes brittle over time, and its connections loosen and run hot. Joining old aluminium to new copper wiring is not recommended, and in a full rewire there is no reason to do it.

Chasing and setting back boxes

Chases are cut with a wall chaser connected to a dust extractor. It makes two parallel cuts and the material between them is chiselled out. There is still a lot of dust, so cover windows, door frames and radiators beforehand. Routes run horizontally and vertically, never diagonally, so their position can be predicted later when drilling. In panel blocks, take care with load-bearing panels. Deep horizontal chases in load-bearing walls are a problem, and the extent of the work must be agreed with the building management, or with a structural engineer if in doubt. For this reason cables are often run in the floor, in a suspended ceiling or in partition walls.

Back boxes are set in plaster or a fast-setting mortar. Heights depend on local practice and your own preferences. A common arrangement is roughly 30 cm above the finished floor for room sockets and roughly 105 to 120 cm for switches. Above a kitchen worktop it is usually around 110 cm. In the bathroom, distances from the bath and shower define the zones where sockets and switches may or may not go.

Cabling and the distribution board

Cables run from the board to the boxes, each circuit separately. Enough spare length is left at each end, and every cable is labelled so nobody has to guess during the second fix. The board enclosure is recessed into a wall in the entrance hall or corridor. It should have spare modules for later additions such as air conditioning or charging an e-bike.

Break for plastering and decorating

After the first fix, the plasterers and drywall fitters move in. Before the chases are covered, the electrician should give you a chance to photograph everything. Photos taken with a tape measure held against the wall will help every time you drill.

Second fix and testing

After decorating and tiling, the sockets and switches go in and the board is wired up. The hob, oven and water heater are connected, and the light fittings are connected to the points. Then comes testing: insulation resistance, earth fault loop impedance, RCD operation and correct connection of the protective conductor. The electrician or inspector then issues a certificate or report on the inspection and testing. You should not use the installation without it, and a missing certificate can cause trouble with an insurance claim.

How long it takes

For a crew of two, the first fix in a 4-room flat usually takes roughly one to two weeks, depending on the wall material and the number of circuits. The second fix tends to take two to four days, and testing usually one day. Between the two stages you need time for plastering, plasterboard, tiling and decorating. Overall, the electrical work is spread over several weeks of the renovation.

Fixed wiring in flats normally uses solid copper installation cable. Lighting circuits are typically 1.5 mm² and socket circuits 2.5 mm². A hob on a three-phase connection needs a five-core cable sized according to the hob manufacturer. In plasterboard, cables run in flexible conduit, and special dry-lining boxes with clamps are used.

For wiring accessories, decide between screwless (push-in) terminals and traditional screw terminals. Screwless terminals are quick and reliable, provided the conductors are stripped correctly. Choose one range of switches and sockets for the whole flat, so the frames match and you can buy more later.

A 30 mA RCD on socket circuits and surge protection are now standard in a new board. For a smart home, with blinds, lighting or heating controlled from an app, decide early. Some systems need a neutral conductor in the switch box or a separate cable back to the board, and adding these later is difficult. Even if you are not planning smart controls now, a neutral in the switch boxes and slightly deeper boxes keep the option open.

The work goes faster and more smoothly when:

• The flat is empty, with no furniture and nobody living there during the work
• Partitions are aerated concrete block or brick and ceilings are plasterboard, so cables are easy to run
• A precise kitchen design and furniture layout are ready
• The renovation is done in one go and the electrician does not have to wait for decisions

It becomes more demanding when:

• Chases are cut into hard concrete panels, where progress is slower and limited by structural constraints
• The layout changes, and with it the position of the board or the kitchen
• The supply from the meter in the stairwell also has to be replaced, which needs agreement with the building management and sometimes the network operator
• People live in the flat during the renovation and the installation has to be replaced in sections
• You want many lighting scenes, LED strips, wall lights and smart controls

The electrician turns up twice in a renovation, and in between their work meets almost every other trade. Before the first fix, demolition should be finished and new partitions decided. The plumber and the electrician need to agree routes so cables and pipes do not cross in the wrong places. They also need to know where the water heater, the washing machine and any electric underfloor heating in the bathroom will go. For heating, check whether the boiler or smart radiator valves need a power supply.

The drywall fitter needs to know where the downlights will be, so a ceiling profile does not end up exactly there. The tiler should have the boxes already set, so the tiles can be cut neatly around them. The kitchen supplier must provide the socket drawing before any chasing starts. Finally the decorator: accessories are fitted only after painting, otherwise they end up covered in paint.

Most mistakes are made during planning, not wiring. Typical situations from practice:

• Too few sockets by the bed and desk, so extension leads multiply around the flat
• Sockets behind kitchen units in places you cannot reach, or no socket for the cooker hood or under-cabinet lighting
• All circuits behind one RCD, so a minor fault cuts power to the whole flat
• Large appliances all on one phase, so the main breaker trips when you cook and wash at the same time
• Diagonal or undocumented routes that end with a drilled cable when someone puts up a shelf
• An unlabelled board where, years later, nobody knows which breaker serves which room
• Loose connections in the board that later show up as heat or a burning smell
• Missing bathroom bonding, which the inspector will flag

Electrical installation work may only be done by a qualified electrician, and this package does not include any wiring steps for you. You can still save the crew time and avoid mistakes by preparing the flat well. These steps involve no work on live parts:

1. Clear the flat of furniture and belongings, or move everything into one room that will be done last.
2. Draw each room to scale with furniture, appliances and the kitchen layout, and mark where you want sockets, switches and lights.
3. Make a list of all large appliances with their rated power, so the electrician can plan the phases and circuits.
4. Cover windows, door frames, radiators and floors with sheeting and tape before chasing starts.
5. Mark the finished floor level on the walls in every room, as agreed with the floor layer.
6. Photograph every wall with the chases open and a tape measure in the picture before plastering, and store the photos with the flat's documents.
7. Keep the stairwell and lift clean and respect the quiet hours agreed with the building management.

At handover, walk through the flat with the electrician and try everything that can be tried. Do not rush, because a 4-room flat has dozens of accessories. Allow at least an hour and check:

• The test certificate or inspection report, dated and signed, with no outstanding defects
• The board schedule, with every breaker and RCD labelled by room
• Each RCD, using its test button
• Every socket, with a socket tester or a phone charger
• Every switch, including two-way switching in the corridor and living room
• The hob, oven, water heater and dishwasher in real use
• Frames fitted straight, with no gaps between the accessory and the tiles
• Photos of cable routes taken before the chases were covered
• Spare modules in the board for later additions
• Warranty terms and a contact for complaints