An isolator is the local switch that lets an engineer cut power to the air conditioner without hunting for the consumer unit. On UK installs it is usually a weatherproof rotary isolator within sight of the outdoor unit. It is an electrical item, specified and fitted by a competent electrician, on a circuit that serves that system. This page explains what you are paying for. It is not a wiring guide.
Making the outdoor unit dead beside the outdoor unit
Service, repair and safe shutdown need a way to make the equipment dead beside the equipment. The isolator does that for the outdoor unit. Some designs also isolate the indoor unit from the same supply, depending on how the manufacturer wires the pair. The electrician follows that diagram, the current wiring rules and the manufacturer's maximum current.
A service switch, not a daily habit
The isolator is not the remote control and it is not a daily on-off switch for the household. Leaving it off for months can be right in a lock-up, and wrong if the system is meant to protect a comms cupboard. Ask the installer which habit suits your unit.
Hidden handles and locked roofs
An isolator hidden behind the condenser, or up a ladder over a stairwell, fails the point of the object. The engineer needs room to open the rotary handle and to see that it is off.
- Local means beside the outdoor unit, not three rooms away.
- Weatherproof housings are the normal outdoor choice.
- A driveway, a side passage and a balcony all change the mounting height.
- If the managing agent locks the roof, the survey should say how an engineer reaches both the unit and the switch.
The circuit ends here, it does not start here
The isolator is the end of a circuit, not a substitute for a dedicated way in the consumer unit or a landlord distribution board. The electrician decides the protective device, the cable route and whether the existing board can take the load. Old boards and full boards are a separate line on the quote. The board protects the circuit. The isolator is the local switch by the equipment so the system can be made safe for service. You want both, specified by the electrician. A local means of isolation for the equipment is standard practice on UK installs. How that is arranged when several outdoors share a plant area is an electrician's design.
A certificate, not only a neat rotary
Ask for electrical certification for the circuit as well as the F-gas paperwork for the refrigerant side. GOV.UK publishes certification for companies working on equipment containing F-gas. A neat rotary switch with no certificate is an unfinished job. You do not need to understand the terminals to insist on that paperwork. Look for supply, isolator, and who employs the electrician. As a 2026 illustration, a straightforward outdoor isolator beside an existing dedicated circuit is often absorbed in the electrical allowance, while a long cable run from a distant board is priced on its own. The survey length is the cost driver. F-gas work and electrical work are different tickets.
When the isolator is treated as the whole electrical design
That approach is wrong when someone treats the rotary switch as a licence to skip the board, or when a householder offers to fit it. It is part of the fixed electrical installation. Use a competent electrician and keep the certificate with the F-gas records. It is also the wrong first spend to match a new condenser to a cracked or undersized old isolator and call that a saving. If a previous unit was disconnected and the old isolator is tired, budget to replace it. The electrician, not the householder, makes that call. Flats sometimes have the supply in a landlord riser and the condenser on a roof. The isolator still needs to be a clear local device for the person working on that machine. Energy Saving Trust's air-to-air pages describe the equipment. They do not describe the terminals.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.