Dedicated Aircon Power Point: Plan It Before Renovation

Dedicated describes ownership of a cable, and nothing else. One run leaves the consumer unit, arrives at the aircon, and feeds no other thing along the way. No socket, no light point, no water heater shares it.

The alternative is a spur taken off a circuit already busy with another job. A general socket circuit serves outlets across several rooms, and an aircon joined to it becomes one more draw among many. Whatever the compressor does is felt at all of them.

None of this is visible at the outlet. A point serving the aircon looks like any other point on any wall, because what makes it dedicated happens back at the board. The labelling on the consumer unit answers it, or the schedule drawn up when the circuit went in.

Treat the word on a quotation as a claim rather than a fact, and ask for the detail behind it. Which way on the board does it land, what protects it, and what size of cable feeds it? A contractor who has planned the circuit has those three answers ready; one who has assumed an existing socket will cope replies in generalities.

Everything described here belongs to fixed electrical installation work. In Singapore only a Licensed Electrical Worker may carry it out, so the homeowner's part is deciding what to ask for and confirming it was done.

Three properties of the load make sharing a bad bargain: its size, how long it stays on, and what it does at the moment of starting. Together they describe a machine that behaves nothing like the appliances a socket circuit was drawn for.

Household loads are mostly brief, and the aircon is not. A kettle draws hard and stops. A compressor settles in and keeps drawing for as long as the room is occupied, which in Singapore means through most of a night for most of the calendar. A cable sized for occasional socket use then spends whole nights loaded.

Starting is the sharper half of the problem. A compressor pulls a surge at the instant it starts, well above what it settles to once running. A fixed-speed compressor does this every time the room calls for cooling, so the surge repeats through the night. An inverter compressor ramps instead of slamming, which softens the step without removing it.

Two symptoms follow, and both get blamed on the wrong component. The first is the trip that only appears when several things run at once, so the aircon is condemned when the circuit is what gave way. The second is voltage sag, where lights on the same run dip as the compressor kicks in.

If a contractor proposes feeding the aircon from an existing socket because the socket happens to be near, ask what else is already on it. Proximity is a routing convenience and says nothing about what the run is carrying. A short cable to a busy circuit is worse than a long cable to an empty one.

In a Singapore flat the provision shows up as two separate things, in two different places. There is a supply point where the system takes power, and there is a means of killing the outdoor unit on its own.

The supply point sits wherever the installer takes power into the system, usually near the indoor unit or out at the ledge. HDB's conditions cap the running current with a 20 amp double-pole isolator or a 15 amp power point. The rating is a specification, not a preference.

The isolator at the outdoor unit exists for whoever has to work on the machine. It makes the outdoor unit dead at the machine itself, without switching the circuit off at the board and without anyone walking back indoors to find out which way did what. It also puts a switch in sight of the person standing at the ledge.

The isolator's exposure is the part nobody plans for. It lives outdoors, takes sun and rain, and its contacts corrode in that air. A failing isolator produces symptoms that read exactly like an outdoor unit fault: nothing at all on a call for cooling, or a system that starts on some attempts and not others.

Earthing runs alongside all of this as a separate requirement with its own rules, and a dedicated circuit does not make it optional. The two get discussed together because they arrive on the same cable.

A new flat arrives with electrical provision already made, and owners read that as the aircon question being answered. What it settles is that a supply exists. Where that supply sits relative to the system going in is a different question.

Which flats need paperwork is settled elsewhere. A flat completed on or after 1 January 1994 carries a 40 amp main switch, and HDB states owners in that group need no permit to install an aircon. Older flats on 30 amp loading turn on whether the job uses an existing approved point or calls for a new one.

The geometry is where the trouble lives. Provision made during construction assumes a system laid out the way the flat was drawn. The owner then decides bedrooms first and living room later, or moves the indoor unit to clear a wardrobe, or picks a system whose outdoor unit wants feeding from a different side.

That gap tends to surface on installation day, the worst possible moment. A crew arrives with a system and a schedule, finds the supply is not where the layout needs it, and the choices collapse to two. Bend the route to reach the supply, or bolt electrical work onto a schedule with no slack.

The circuit is decided at the cheapest moment of a renovation and revisited at the dearest one. Cable routes get set while walls are open and ceilings are not yet closed; everything afterwards is finishes going on top of a decision already taken.

A circuit added after the finishes has two possible routes, and neither is the one anyone wanted. The first is chasing: cutting a channel into a finished wall, then making good the plaster and repainting. The second is surface trunking, which leaves the cable in a visible box crossing a wall the owner just paid to finish.

This gets missed without anyone being careless. Electrical work happens early, when the aircon is still a brand and a rough room count. The layout firms up later, once quotes have come back and a system has been chosen. Two trades, two moments, and the information joining them arrives after the first has packed up.

Pull the aircon layout forward to the electrical stage instead of the installation stage. The room count, the outdoor location and the intended supply position are enough to work with, and none of that needs a signed aircon contract.

Framing these as questions matters, because a homeowner is not meant to specify a circuit. Deciding what to ask for and confirming it happened is the whole of the owner's job here.

Ask them while the walls are open, at the point the electrical scope is being agreed. The same questions asked after the plastering is done are a different conversation with a different bill.

• •Is the aircon on a run of its own from the board, or is it joining an existing circuit?
• •If it is joining one, what else is already on that circuit?
• •Where exactly is the supply point going, and which side of which wall does it land on?
• •Does that position match where the indoor units and the outdoor unit are actually planned?
• •Is there an isolator at the outdoor unit, and can it be reached from where someone would stand to work?
• •What cable size and what device rating has the circuit been designed around?
• •How many free ways will the consumer unit have left once this job is finished?
• •If another system gets added for a room not being done now, what would that need?
• •Who is the Licensed Electrical Worker responsible, and what record of the work will be handed over?