Electrical connections

Cabling and electrical connections.

Wiring configuration

Example outdoor unit wiring The majority of mini-split units rely on a well-earthed, RCD protected, mains supply to the outdoor unit. A four-core cable then passes power and control signals to the indoor unit. This cable is often run alongside the insulated refrigerant lines (i.e. not directly against the copper pipework).

A small minority of systems require power supplied to the indoor unit, with a control cable to the outdoor unit. This configuration is more unusual because the outdoor unit uses more power and therefore a heavier duty cable is required between the units. However, it has the advantage of simpler outdoor wiring, using just one cable.

Types of cable

The considerations for the cable are:

  • Rating - the size of the copper cores
    Most mini-splits require 2.5mm2 cable for the main feed and 1.5mm2 interconnect cable. The manufacturer specifications and installation instructions should have the details. Remember, bigger cable is OK, smaller isn’t!

  • Outdoor rated cable
    Example outdoor unit wiring Outdoor cabling should be outdoor rated! For the main power connection use outdoor rated 3 core cable which is easy to source.

    For the control cable, many air-con suppliers offer four core SY cable which has a strong outer steel braid. However, most SY cable is not UV resistant, meaning it must be protected from sunlight - a black plastic flexible conduit is a good option. Alternatively, a more specialist and expensive UV rated cable can be used.

    - RS components website Opens in a new window has an interesting article on SY cable.
    - Byson cables Opens in a new window are one company who offer a range of tough and UV resistant cables.

  • Connection terminations
    Some manufacturers recommend terminating the cable cores with ring terminals. This helps make a stable and reliable connection in the stressed environment of the outdoor unit.

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