Ok. I just had an 18btu aircon moved from one rental house to another. The installers were a pair of cowboys.. I didn't realise until half way through.. Anyway I tried keeping an eye on them and noticed that they had prepared two wires from the internal unit ready for twist and go. I told them NO, Do it properly.. Ok, ok they say.. After they left it seemed to be working OK.. Next day not so well. So out with steps and bugger me I could see a bit of taped wire sticking out the top.. So I called a different (professional) outfit to clean the three other aircon and install plastic ducting covers over the outside pipework.. Also their job was to sort out the wiring ie: do it correctly and not twisted and taped.. Finally they understand what I mean (the air was working, so they couldn't see a problem) they took the outer cover off and looked at the wiring and said "no problem".

So my questions:

Is it a problem to have the main feed to the internal unit just twisted and taped?

How do proper aircon installers connect the main electrical feed?

Ideally, the feed should go through an isolator, so no tape and joints. Unfortunately this is thailand, so twist and taped is commonplace.

And is that OK for an aircon. They have fairly high start up loads (I think) I certainly don't want a problem with the wiring overheating and catching fire or something silly!

Yes, just fine, if the twist and tape is done correctly, arguably better than an isolator ( which is just regulation in most western countries)

Unfortunately the twist-n-tape is not necessarily done properly. The cheapo PVC tape available here has a nasty habit of going gooey and then dropping off, if they have used proper jointer's amalgamating tape, no issue whatever. This stuff http://solutions.3m.co.uk/wps/portal/3M/en_GB/ElectricalMkts/ElectricalSupplies/products/electrical-tapes/self-amalgamating-tape/ yes, it's available here (even Tesco have it).

Replace with proper wire-nuts, some like a twist of tape on the nut too, it's not really needed if they are the right size.

Thanks. I'm just a bit pissed off that two separate aircon guys couldn't be bothered doing it properly.. As in connecting a new piece of wiring directly to the aircon and switch box.. It seems they wanted to save me money by using the old cabling!

If you can make a Western Union splice https://en.wikipedia.org/wiki/Western_Union_splice it's going nowhere (diagrams E and F are variants), wire nuts are rather faster,

Thanks

Wire nuts. Simple. secure. Size depends on wire gauge, probably yellow ones for your job.