Airconditioner Cabling Point

[regedit]

Should the cable from the distribution board run to the unit that is fitted inside the room or to the box that sits outside ? I know the aircon fitters connect two, but just wondering which unit should recieve the power from the main board. Thanks.

[Khun Jean]

The inside unit, it contains the logic to switch on the external unit.

[bankruatsteve]

The inside unit, it contains the logic to switch on the external unit.

Hmmm. When under construction, I ran cable to both inside and outside b/c I wasn't sure how they would want it. The A/C guys preferred the outside one with "normal" installation has the wires from that to the inside unit. I have Mitsubichi A/C.

[Tywais]

To the outside unit as it requires the most operating current. The inside unit gets its power from the outside unit distribution block and only requires smaller gauge wire as the current demands are much smaller.

[Khun Jean]

Well that is great.

So all 3 of my aircons in the condo and the one just installed a few weeks ago in the shop are wired wrong, or at least not the most optimum way.

Does that mean that in the outside unit there is a relay to switch on the outside unit from the inside units control circuits requiring only a thin switching wire (1mm should be enough for that)?

I will have a look at the manual of those if i can find it.

Edited December 28, 2012 by Khun Jean

[Tywais]

Working with dozens of AC units over the years, the way I mentioned is what I have seen. It is possible to do it the other way but I would consider it more hazardous carrying the high startup currents through the inside unit to the outside. No relays needed. The outside unit has the mains power coming into it and that is fed off via a distribution block via a feed line to the inside unit along with control signals going back to the outside unit from the control unit. Note below, Hard Wired is referring coming from the mains distribution panel. Note the direction of the arrow for electricity, that is the AC feed from the outdoor unit to the inside unit.

[Khun Jean]

I looked at a few manuals on internet from mitsubishi and they use a powersupply on both ends and connecting the in and outside units with a 2x1mm wire.

If this is the case with the one that is installed in our small shop i can bet they saved on wire and pulled a 2x1mm wire to the outside unit for powering the outside unit leaving out the all important earthing wire not tomention the much to thin wire. Before i go crazy i will have a check one of these days by removing the tape around the pipes and wires and see what is really there. I am already almost certain they not followed the instructions because i only saw him using the 2-core 1mm wire. I was not there all the time as i should.

I guess i have to take out another profession of the list that 'proffesionals' are capable doing here in Thailand. That unit was bought in Home Pro Bang Na and they used a small contractor to install it.

[Khun Jean]

Thanks for the pic Tywais.

Makes it very clear.

The way ours are wired is not like that.

As no new wires where installed to the CU they must have extended the wires that went from the indoor unit to the outside unit.

Pretty silly as the distance from the outdoor unit to the CU is about 3 meters and the distance to the indoor unit is 8 meter.

As is suspect now is that the power supply extensions made from 2-core 1mm wire as that was all they used.

A fire hazard as it is way to thin and probably detrimental to the correct working of the outside unit because of voltage drop and higher resistance when those wires get warm. And as they are wrapped with tape with the control wires and copper tubes it just adds another danger as when one of those cables would melt it could short with the copper pipes. It would probably also mean that the outside units are not earthed and as such pose a hazard too because they can be touched easily.

I just switched of the breakers to the airconditioners until i have this resolved.

[GavinK]

Outside unit it is then ! This also helps me.

Edited December 28, 2012 by GavinK

[Khun Jean]

Outside unit it is then ! This also helps me.

If you know make and model i guess you can look it up on internet.

The ones from Mitsubishi seem to connect bot units to their own direct power and use only a thin 2-core wire for control between the in and outside unit.

I guess it all depends on the distance between CU and the units.

[Tywais]

Wonder where Naam is? He can sniff these AC topics out from a mile away.

[electau]

A complete wiring diagram is supplied with the airconditioner, use that, it will give the correct size of cable and protective device for the circuit from the switchboard.

[Langsuan Man]

Unless you take off the large conduit that is between the outside unit (compressor) and the inside unit you will not know how it was wired. I have two (outside) units on my balconey and I know that they pulled the "hot wire" from the attic to power the A/C and that power cable goes into the conduit. Unless I remove the conduit I don't know where the wires went

I am going to install two additional units in the downstairs and have had two sets of three wires run from the main power switch box to the locations via the "drop down" ceiling per the instructions of the technician who installed the first two units. At no time was I told to provide seperate power to the compressor units and am going to assume that the people that I pay to install my A/C know what they are talking about

[Khun Jean]

As i understand from this part of the manual each unit has their own connection to a power supply.

[Crossy]

As can be seen from Jean's diagram, it matters not a jot which unit gets mains power as there will always be a power cable between the two (unless you feed individually from your distribution board).

1mm² cable is good for 13A (3kW) or so, that would power a 30,000 BTU outdoor unit without being any form of hazard (of course, a ground is required). Not the correct interconnect cable for such a big unit mind due to volt drop on startup surge.

All our current A/Cs have power to the indoor units, all the units we had in India had power to the outdoor units, both arrangements function just fine.

[regedit]

Many thanks for clearing this up Crossy.

[electau]

Generally the circuit is run from the switchboard to a switch adjacent to the compressor unit and a multi core cable is run from the compressor ( terminal block) to the fan coil unit.

The switch should be IP56 rated ( weatherproof). For a 3.0kW input power unit, cable size 2.5sq mm, 20A MCB or RCBO.

Edited January 2, 2013 by electau