The short answer
Most wall-mounted systems need their own circuit from the consumer unit, often with an isolator switch near the outdoor unit. In England and Wales a new circuit is notifiable building work, so it's done by a registered electrician or notified to building control.
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The electrical side of an installation is simpler than the refrigerant work, but it has its own rules and its own paperwork. A single wall-mounted split uses much less power than an electric shower, yet it still needs the right circuit, the right protection and a certificate to show the work was done properly.
A dedicated circuit
Most systems need their own circuit running from the consumer unit, rather than a plug in a socket or a connection to an existing circuit. The manufacturer's instructions say what's required, including the size of the circuit breaker and the cable.
A circuit of its own means the system isn't sharing capacity with other appliances, and it can be switched off by itself when an engineer needs to work on it.
On many models the power supply goes to the outdoor unit, and a connecting cable carries power and control signals on to the indoor unit. On others it's the other way round. Either way, that connecting cable runs through the wall in the same bundle as the refrigerant pipes.
What gets fitted
| Part | Where it goes | What it's for |
|---|---|---|
| Circuit breaker | Consumer unit | Protects the new circuit |
| Supply cable | Consumer unit to the system | Carries the power |
| Isolator switch | Often beside the outdoor unit | Cuts the power for safe working |
| Connecting cable | Between the two units | Power and control signals |
The circuit is protected by a breaker at the consumer unit, and usually by an RCD too, often combined with the breaker in one device called an RCBO. An RCD switches the power off quickly if current leaks to earth.
Outside, cables need to be suitable for outdoor use and protected from damage. They often run inside the pipe covers, or in armoured cable where they need extra protection.
Your consumer unit
Adding a circuit needs a spare space in the consumer unit, or room to add one. An older consumer unit may need work before a new circuit can be connected, which can add time and sometimes a separate visit.
When adding a circuit, the electrician checks that your home's existing earthing and bonding are adequate. With several indoor units, or other large loads such as an electric vehicle charger, they also consider whether your electricity supply can take the combined demand.
Your power is switched off while the new circuit is connected to the consumer unit, so expect to be without electricity for part of the day. How much a system uses once it's running is covered in does air conditioning use a lot of electricity?
Building regulations and paperwork
In England and Wales, a new circuit is notifiable under Part P of the Building Regulations. It must either be done by an electrician registered with a competent person scheme, or be notified to building control. Scotland and Northern Ireland have their own building rules, so check what applies if you live there. The wider picture is in building regulations.
For a new circuit you should receive an Electrical Installation Certificate, which records how the circuit was designed, installed and tested. If the electrician is registered with a competent person scheme, you should also receive confirmation that the work complies with the Building Regulations.
Keep these with the rest of the installation documents, described in commissioning and handover. They're useful if something goes wrong, and buyers' solicitors often ask for them when you sell.
Who does the work
Some air conditioning engineers are also qualified electricians and do both jobs. Others bring in an electrician for the circuit, sometimes on the same day as the installation and sometimes on another. Either arrangement is normal.
What matters is that the person doing the electrical work is competent and the work is certified. When you get a quote, ask:
- Who will do the electrical work, and are they registered with a competent person scheme?
- Where will the cable run from the consumer unit to the system?
- Does your consumer unit need any work first?
- Which certificates will you receive afterwards?
The step-by-step order of the day, including when the power goes off, is in what happens on installation day.
Related guides
- Building regulationsThe part of the building regulations that most often affects an air conditioning installation is the electrical work. In England and Wales a new circuit is notifiable, so it's done by a registered electrician or notified to building control.
- What happens on installation dayInstallers fix the indoor and outdoor units, link them with insulated pipes through a hole in the wall, test the pipework for leaks and clear it of air, then connect the power, run the system and show you how to use it.
- Commissioning and handoverCommissioning is the set of tests that prove a new system is sealed, safe and working as designed. Handover is when the engineer shows you how to use and look after it and gives you the records and certificates to keep.
- Does air conditioning use a lot of electricity?Less than its size suggests: a wall-mounted unit's kW rating is the heat it moves, and it usually draws a fraction of that in electricity. The total depends mainly on how many hours it runs and how hard it has to work.