Split Air Con Wiring Question

[Jonny66]

Hi,
Need some advice regarding running cable for - split air conditioning unit (Mitsubishi Heavy Industries Air Conditioning SRK40HG-S Wall Mounted, 3.6kW / 13200 Btu Heat pump Fixed speed Split Type)


The pipe work has been installed but the client cant get hold of the installers and no manuals as units being re-used. I have been asked to run out a supply to the AC unit but have not wired ac units before. The cable needs to run under the floor, which is due to have laminate flooring laid over it on Monday.


I’m a little unsure how to run out cable to a split AC unit.

Do I run 3 core cable from the DB to the inside cassette, and then to the outside unit via and isolator?

Or do I go from DB to outside isolator/unit and then another cable back to inside cassette?


I know probably basic questions, but need to get correct cable in before laminate goes down.

Appreciate any help

 

[Marvo]

Nearly always with a high wall split you would run power to the outdoor unit using standard T+E cable and mount a DP isolator next to it if it's single phase. Usually they would run a cable between the outdoor and indoor unit along with the pipework. This cable is often a 4 core plus earth depending on the model, it can often be a smaller CSA size (1.5mm) as well due to the relatively low power requirements of the indoor unit.

If you're unsure about the supply and interconnection wiring please get a qualified electrician to install, it will be cheaper than damaging the unit. Also this work would require signing off and certification to be a legal and safe installation.

 

[Jonny66]

Thanks Marvo,
The outside unit is mounted on a flat roof so will run out 2.5mm 3 core SY cable to outside isolator, and 5 core SY back to indoor unit.

 

[Marvo]

Thanks Marvo,
The outside unit is mounted on a flat roof so will run out 2.5mm 3 core SY cable to outside isolator, and 5 core SY back to indoor unit.

I would use twin and earth for the supply and 4 core + e surfix for the interconnecting cable.

It's always worth checking the installation manual but I'm sure that will be fine. There's been a few discussions on here about using flex as installation cable and from what I can gather it's not illegal in the UK but it's considered bad practice by many. Also you must use crimped lugs for all terminations with SY cable due to the conductors being fine stranded.

 

[Jonny66]

Fair point regarding crimped lugs. But as outside unit and isolator are mounted on flat roof and around a meter from the external wall, would T&E be suitable for external conditions and it may also be difficult to keep IP rating of isolator using T&E.

 

[Marvo]

Black surfix is UV stable so the interconnect cable wouldn't be a problem, you could use SY if it's strapped in under the pipes. I wouldn't clip T+E direct if it's external, conduit and male adapter into the isolator would be required. I'm not sure about SY cable, I've never used it for outdoor installation work but I don't think that's UV stable either.

IP rating shouldn't be a problem which ever way you go if the right glands are used. I don't know about the UK but SY costs a lot more here than T+E does so that might also be a consideration.