Electrical rewiring in a one-room flat: first and second fix

Electricians split the job into two stages, and other trades work in between.

First fix happens before plastering and tiling. The electrician marks the cable routes, cuts chases into the walls, sets back boxes for switches and sockets, pulls in the cables and prepares the position for the consumer unit. At the end of this stage only cable ends stick out of the walls.

Second fix comes after decorating, once the walls are finished. The electrician fits switch and socket fronts, connects the circuit breakers in the consumer unit, connects outlets for lights, cooker and water heater, and tests the whole installation.

A one-room flat usually means a hallway, one living room, a kitchen or kitchenette, and a bathroom and WC, which are often combined. It may be a true studio with the kitchen in the living space, or one room with a separate kitchen. Contractors differ on whether the package includes materials, making good the chases, fitting light fittings and the final certificate. Go through the quote line by line.

NUMIQ lists each flat size as a separate item. The difference is not only metres of cable. As the number of rooms grows, the consumer unit, the number of circuits, the time on site and the way the work is organised all change.

• One-room flat (this item): small floor area, short cable runs, one living room. Most of the work is in the kitchen and bathroom, not in the room itself. The consumer unit is compact, usually with around ten circuits. Two electricians can usually finish first fix in a few days.
• Two-room flat: one more room, which usually means another lighting and socket circuit. The consumer unit needs more modules, and runs from the hallway get longer.
• Three-room flat: circuits are split by room and zone. A larger consumer unit is the norm, and with higher demand the size of the main supply fuse becomes a real question.
• Four-room and five-room flats: many circuits, often two bathrooms, a bigger kitchen, data cabling to several rooms. The job takes longer, and without a detailed plan it is hard to keep it under control.

A small flat has one particular feature: the kitchen takes a large share of both the power demand and the sockets. Hob, oven, dishwasher, fridge, microwave, kettle and often the washing machine all sit within a few metres. So do not cut back on dedicated kitchen circuits just because the flat is small. In a studio with a kitchenette, think carefully about where the kitchen units go and where the bed or sofa goes, because the same wall often serves both.

If you are unsure whether this item or the two-room package fits your flat, count the real living rooms. A flat with one room and a separate kitchen is still a one-room flat. The kitchen does not count as a room, even if it gets a few extra sockets.

A plan for sockets, switches and lights

Often the electrician arrives at an empty flat and the owner decides socket positions on the spot by pointing at walls. It works, but a simple sketch of each room helps a lot:

• Where the kitchen units go, how high the worktop is and where the appliances stand
• Where the bed, sofa, TV and desk will be
• Whether the washing machine goes in the bathroom or the kitchen
• Where the ceiling light goes, and whether you want lights under the wall units, by the mirror, or two-way switching in the hallway
• Whether you want a data cable to the TV and router, and a doorbell or door entry phone

Ideally the kitchen is designed by the kitchen supplier before first fix. A socket hidden behind a cabinet or an oven outlet on the wrong side is hard to move later and means cutting into fresh plaster.

The building and the managing agent

In a block of flats, not everything belongs to you. The meter cupboard in the corridor, the riser cables and the main fuse before the meter belong to the building or the network operator and are usually sealed. Before work starts, contact the building management or the owners' association. They can tell you who may switch off the supply to the flat, which rules apply to noisy work, and where rubble can go. If you need a larger supply, for example for an induction hob and an electric water heater at the same time, you arrange it through your electricity supplier and the network operator, never by yourself.

Building regulations

Replacing the wiring is a normal part of a renovation. If you are also removing partition walls, making new openings or changing the layout, ask your local building authority which procedure applies. Some countries also require notifiable electrical work to be certified or registered. Your electrician should know the local rules, but confirm it before work starts.

Getting the flat ready

The flat should be cleared, with access arranged and a temporary power supply for tools. The electrician usually sets that up as a site socket next to the consumer unit. It helps to know where water pipes and any gas pipes run, so nobody drills into them while chasing. Gas pipework is a job for a qualified, registered gas engineer only. If you smell gas, leave the flat, do not switch any appliances or lights on or off, and call the local emergency number or 112.

Stripping out the old wiring

The electrician first isolates the flat and checks that nothing is live. The old consumer unit, switches, sockets and light fittings come out. Old cables are either pulled out or disconnected and left in the wall. In concrete panel blocks the old aluminium wiring is often left dead in its chases, because pulling it would destroy a lot of plaster. What matters is that no old cable stays connected, so nobody can use it by mistake later.

Marking routes, chases and back boxes

Cables run vertically and horizontally, never diagonally. This is for safety: anyone drilling a hole for a shelf later can guess where a cable might be. Horizontal runs usually sit just below the ceiling or just above the floor, vertical runs directly above and below the boxes. Chases are cut with a wall chaser connected to a dust extractor, holes for back boxes are drilled with a core bit, and the boxes are set in plaster or adhesive. Agree socket and switch heights in advance and keep them the same throughout the flat.

Cables and the consumer unit

Lighting circuits usually use copper cable with a 1.5 mm² cross-section, socket circuits 2.5 mm². The cooker or hob normally gets its own supply, depending on the hob and the supply sometimes three-phase. The washing machine, dishwasher, oven and an electric water heater, if you have one, each get a dedicated circuit. In the bathroom, the zones around the bath and shower decide where sockets and switches are not allowed. These rules come from the wiring standards based on IEC 60364, adopted in Europe as HD 60364, and from your national wiring regulations. A qualified electrician works to them every day.

The consumer unit usually stays in the hallway where the old one was, because that is where the supply from the corridor comes in. A new enclosure goes in with enough modules and some spare space. It holds circuit breakers for each circuit and residual current protection, on socket circuits typically with a 30 mA rating. Depending on the situation, surge protection is added. Before the chases are covered, photograph the whole flat so you know later where the cables run.

Cable routes in concrete and brick buildings

In a brick building chases can be cut fairly freely, as long as load-bearing walls and lintels are respected. In a concrete panel block it is different. Load-bearing panels should not be chased deeply, especially horizontally, because this weakens the structure and the concrete contains reinforcement. The electrician therefore looks for other routes:

• Existing chases: the new cable goes into the route of the old wiring, if its condition allows
• Floor: if a new floor is going in, cables in conduit run underneath and only rise a short way into the walls
• Partition walls: non-load-bearing block or plasterboard partitions are easier to chase
• Boxed-in walls and suspended ceilings: in the bathroom and above the kitchen, cables can be hidden behind plasterboard
• Surface trunking: where there is no other way, trunking works, even if it is not pretty

Older blocks sometimes have a prefabricated bathroom pod. If it is being replaced with a built bathroom, plan the wiring together with the new partitions and the plumbing.

Second fix

After plastering, tiling and painting, the electrician comes back. Switch and socket fronts go on, outlets for lights, cooker and water heater are connected, and the consumer unit is wired and labelled. Whether light fittings are included depends on the agreement. Sometimes they are part of the package, sometimes only a connector is left and you hang the lights later.

Testing and certification

At the end the installation is tested: insulation resistance, earth loop impedance, RCD operation and correct connection of the protective conductor. You then receive an electrical installation certificate with the test results. Without it you should not put the installation into use. The certificate is also useful when you sell the flat or deal with an insurance claim.

Even for the same size of flat, the work can take very different amounts of time. It is easier when:

• The flat is empty and ready for rough work
• There is a kitchen plan and a furniture layout
• A new floor and new plaster are coming anyway, so chases do no harm
• The walls are made of material that is easy to chase
• The supply from the corridor is in good order and does not need replacing

The work gets longer and more complicated with:

• A flat that is lived in or still full of belongings
• Load-bearing concrete walls, where alternative routes have to be found
• Existing tiles or plaster that must stay undamaged
• Last-minute changes, when boxes get moved after chasing
• A damaged or undersized supply cable to the flat, which has to be sorted out with the building
• Many special requests: several lighting circuits, LED strips, data points on every wall

The electrician comes at the start of a renovation. A typical order in a one-room flat is: demolition, electrical first fix, water and waste pipes, new partitions and ceilings, plastering or skimming, floors and tiling, decorating, electrical second fix, kitchen fitting and finally certification.

Points to coordinate:

• Plumber: boxes for the washing machine and water heater must line up with the water connections
• Tiler: boxes in tiled walls are best set out so they fall on a joint line or in the middle of a tile
• Kitchen supplier: worktop height and appliance positions decide where sockets go
• Drylining installer: cables for ceilings and boxed-in walls must be in place before the boards go up

First fix in a one-room flat usually takes two to four working days for two electricians, depending on the walls and the scope. Between first and second fix there is time for plastering, tiling and decorating, often several weeks. Second fix with testing usually takes one day, and certification another short visit. Chases are made good only after the routes have been checked. Plaster filling needs a few hours to a day before work can continue, depending on the manufacturer.

• Too few sockets at the worktop: a year later you cook with an extension lead across the counter. In a small kitchen, plan sockets above the worktop in several places.
• Everything on one circuit: with oven, kettle and washing machine running together, the breaker trips. Dedicated circuits for large appliances prevent this.
• Joining aluminium and copper: if new copper cable is joined to old aluminium in an unsuitable way, the joint heats up and can start a fire. In a full rewire the old wiring is disconnected completely.
• No residual current protection: everything works, but protection against electric shock is missing. Testing will reveal it.
• Sockets behind cabinets: a box that ends up behind a cabinet side or the fridge is useless. Without a kitchen plan this happens easily.
• Switch behind the door: if the door opens towards the switch, you have to reach behind it. Check which way each door opens beforehand.
• Unlabelled consumer unit: a year later nobody knows which breaker serves the bathroom. Circuit labels belong to the handover.
• No photos: someone drills through a cable while hanging a shelf. Photos of the routes before plastering take almost no effort.

Why do some faults only show up later? A new installation lights up and works on day one. Weak points only appear under everyday load, for example in winter when a heater, the oven and the washing machine all run at once.

All wiring, connections and anything live are strictly for a qualified electrician. What you can do yourself is the preparation, which saves time on site and avoids most of the mistakes above.

1. Clear the flat completely, including old shelves and fittings that the electrician is not removing.
2. Get the kitchen plan from your supplier, with worktop height and appliance positions.
3. Draw a simple floor plan of every room and mark the bed, sofa, TV, desk and wardrobe.
4. Mark on the plan each socket, switch and light, and note which way every door opens.
5. Decide where the washing machine and water heater go and tell the plumber the same.
6. List extra wishes such as two-way switching, LED strips, data points or a door entry phone.
7. Ask the building management who switches off the supply and when noisy work is allowed.
8. Walk through the flat with the electrician before chasing, and photograph all routes before plastering.

At handover, ask to be shown the consumer unit and go through the flat room by room. Press the test button on the RCD, which should switch off immediately. Turn on every light and try every switch. You can plug a normal appliance or a simple plug-in socket tester into each socket. Do not open anything inside the installation, as that is work for the electrician.

• Electrical installation certificate handed over and signed
• All circuits labelled in the consumer unit and matching reality
• RCD trips when the test button is pressed
• All sockets and switches firmly fixed, level and at the agreed height
• Every light switches on from all agreed positions
• Separate outlets ready for cooker, oven, dishwasher, washing machine and water heater
• No sockets or switches in prohibited bathroom zones
• Unused old wiring disconnected and insulated
• Photos of cable routes before plastering in your hands
• Data and aerial cables terminated and labelled
• Area around boxes and the consumer unit made good and clean