Common first fix electrics tasks

Getting the electrics right at the first fix stage is key to making sure your clients are happy in the long-term with their bathroom fixtures and fittings.

Experience has taught you just how many crucial tasks there are for you to carry out during the first fix stage. As well as taking care of the bathroom plumbing, this is the time to lay down the cables and other electrical components that will keep the bathroom running smoothly for years to come.

When the work done at this stage has been done well, the client won’t notice it at all. If it’s been done badly, however, addressing the issues can involve major upheaval. That’s why it’s important to remind yourself exactly what is expected well in advance.

  • 1. Assessing the scale of the work

    Some bathroom designs require minimal electrical work at the first fix stage, but for others, this will be a major part of the job.

    During initial planning, you will probably have already come up with an estimate for the amount of time this stage will take. However, it’s worth revisiting this estimate once you’ve already finished demolishing the existing bathroom and have a better understanding of the space.

    Ask these key questions to establish a realistic idea of the work required with your client:

    How accessible are the areas you need to reach?

    If you’re installing new cabling, can you simply put it beneath the floor covering, or will you need to lift the floorboards and the skirting boards?

    Are you installing electrics in the ceiling? If so, make sure you survey possible access points from both above and below. We’ve all experienced awkward moments where a bad approach to the fittings increases the difficulty of the task.

    Are new spaces for cabling needed?

    If no channels for cables already exist where they are needed, you’ll need to create them yourself. Naturally, this adds a lot of extra time if you’re doing this for the walls, ceiling and floor.

    How many items need to be powered?

    At the very least, you’re likely to be rewiring the lights. But you may also have to fit underfloor heating, reposition shaver sockets and other outlets, install an extractor fan, put in a shower pump or fit more complex lighting solutions such as spotlights or illuminated mirror cabinets. All of these items will need to be powered, which can mean laying cables all over the room.

    Do you have the right people for the job?

    It bears repeating that electrical work can only be carried out by a certified electrician, delegating to someone else if necessary. If it seems that the electrical work required will be very extensive, hire an electrician and factor it into your initial quote.

  • 2. Common first fix electrical tasks

    All kinds of different jobs might need to be undertaken at the first fix stage, but here are a few of the most common tasks you probably attend to most frequently.

    Rewiring lighting

    Rewiring lighting and installing light fittings are amongst the most fundamental electrical requirements for most bathroom renovations. Some bathroom designs only call for a single light in the wall or ceiling. You’ve probably noticed, however, that most require more extensive work.

    Many modern bathroom ideas involve recessed spotlights. These call for some extra work. You’ll need to carefully measure and cut holes for the lights in the ceiling, as well as laying the necessary cables. Make sure the area you’ve chosen for each light is not obstructed by any joists or supports concealed in the ceiling.

    The ceiling work required at the first fix stage can be quite time-consuming, especially if spotlights are involved. Consider using a workstand.

    Ask your client if they would like additional lights, for example around the bathroom mirror, inside the cabinets or over the shower. It doesn’t always occur to clients that these lights are useful until after the job is completed, and at that point installing new cables is a lot more disruptive.

    Installing underfloor heating

    Underfloor heating was once considered a luxury, but it’s increasingly seen by many as a bathroom must-have.

    Installing underfloor heating involves a few different processes at the first fix stage. These include fitting a switched fuse spur and laying the wires for the thermostat, as well as placing the heating wire and temperature sensor.

    Find more detailed tips on installing underfloor heating in our underfloor heating section.

    You can also learn more by watching Flexel’s video on how to install underfloor heating.

    Adding or moving shaver sockets

    Shaver sockets are usually located next to the bathroom mirror. If you plan to move the shaver socket or install a new one, you’ll need to run new cables through the wall and fit a back box in preparation. The socket itself will be added at the second fix stage.

    Fitting an extractor fan

    Most bathrooms need an extractor fan to prevent problems with damp and to keep the air in the room feeling and smelling fresh. At this stage, you’ll need to have calculated what size of extractor fan is needed for the bathroom, and where best to place it.

    Find detailed advice on extractor fan installation in our extractor fan section.

    Manrose wall fan

    Shower pump

    A shower pump can be connected to the electrical supply from a 230v switched spur off a ring main. It should never be connected to the supply of the cylinder immersion heater or any other high-load installation.

    You should always be able to isolate the water supply both to and from the pump. Fit a 22mm full bore isolating valve to the cold water pipe that supplies the pump. Generally, the pipework should be 22mm to reduce flow resistance to and from the pump. Best practice dictates that the pump should be supplied through 22mm pipework whether it has 22mm or 15mm connections.

    You can use flexible hoses supplied with your shower pump to link to both the incoming supply and the outgoing delivery pipes. These are less prone to vibration from the pump, reduce noise and prevent damage.

    The pipework should be thoroughly flushed prior to connecting the pump to prevent debris impairing its operation.

    Selco shower pump

    Putting in additional circuits and outlets

    Certain items need a 15-amp or 20-amp circuit of their own. If you’re fitting floor heating, a whirlpool tub or a towel warmer, you should consider whether you’ll have to install separate circuits.

    Ask your client how many outlets they think they will need in the bathroom, and what kind of appliances they use. Straightening irons, hair dryers and curling irons are all commonly used. A variety of outlets, of course, could mean several circuits.

    An instantaneous electric shower requires a dedicated radial circuit running from the consumer unit. An electrician should use a heavy-duty 10mm² cable for the circuit and install a separate RCD fuse unit for the shower.

    A shower circuit must have a double pole isolator switch (disconnects both live and neutral). For small bathrooms, the switch may need installing outside of the room. If you’re working on a large bathroom and wish to install the switch in the room it must be of a pull cord type, generally located on the ceiling.

  • 3. Some notes on cable

    During the first fix stage, you’ll be working with different kinds of cable. Choose the right type for each task and expose the wire of the cable ready for installation.


    The most common type of cable is two-core-and-earth cable. As you probably know, inside, the live core has brown insulation, the neutral core has blue insulation, and the earth core is uninsulated.

    Three-core-and-earth cable should be used for lights requiring two-way switching. The cores inside this kind of cable will be brown, black and grey, with an additional uninsulated earth core.

    Always protect the bare earth cores using green and yellow electrical sleeving before connecting the cable.

    Cable most commonly comes in diameters of 1, 1.5, 2.5, 4, 6 and 10mm2. Decide which size you need based on the current demand of the circuit and the bathroom fixtures it connects to. As ever, higher current demands need bigger cables.


  • What is the best method for wiring an extractor fan?

    Since extractor fans usually connect to light circuits, wiring them at the second fix stage is usually just a matter of connecting up the cable you’ve already laid.

    Further information on extractor fan wiring >>>

  • How do I add light fittings in the bathroom?

    This very much depends on the kind of lights you’re fitting, but by the second fix stage, you’ll already have laid down all the cables you need. At this point, you might need to connect up a pendant light, or slot ceiling spotlights into position.

  • What are the benefits of a timer fan?

    Timer fans are more efficient than basic or humidistat fans. This is because they come on every time the bathroom light is switched on, and stay working for a set amount of time after the light has been switched off.

  • Where is the best place to fit an extractor fan?

    This will depend on the layout of the bathroom and whether you think the fan will be best placed on a wall leading to the exterior or built into the ceiling. To prevent mould inside, the fan vents should process the damp air outside the building.

    It is also important to consider the placement of the cables, ensuring that wiring can easily connects to the lighting circuit.

    Learn more about where to place an extractor fan >>>

  • How do I fit an extractor fan?

    First, calculate what size of extractor fan is needed for the bathroom, and where best to place it. Then you’ll want to follow these key steps to install the extractor fan:

    • Position the fan
    • Install the duct pipe
    • Finish the wiring

    Find more advice on extractor fan installation >>>

  • How do I install underfloor heating?

    Start by fitting a switched fuse spur and laying the wires for the thermostat, as well as placing the heating wire and temperature sensor.

    To see the full guide, find more detailed tips on installing underfloor heating >>>