Aircon Surge Protection: Where It Sits Decides Its Reach

A surge is a brief, violent rise in voltage on an otherwise normally working circuit. It arrives and leaves faster than anything mechanical can answer. Nothing switches off, no protective device moves, and the supply is still there afterwards. What changed is what the electronics were exposed to while it passed.

Lightning reaches equipment by four routes, and only two need the building to be struck. IEC 62305-1, the standard behind Singapore's SS 555 series, names them: a flash to the structure, a flash near it, a flash to a connected line, and a flash near such a line. The last two matter most to a household, and neither needs anything on the roof.

The damage that follows is attributed to the lines as often as to the strike point. Overvoltages induced on connected lines get transmitted into the structure and travel the same conductors as everything else. A flash at or beside the building also couples into equipment through the field it throws. Both mechanisms finish in the same place: whatever electronics happened to be energised.

Singapore hands those routes an unusual number of chances. The Meteorological Service Singapore puts the average at about 176 lightning days a year, one of the highest rates in the world. A parliamentary reply from the Ministry of Sustainability and the Environment states the same figure as lightning on one day in every two. Activity peaks in November, then April and May.

Not every surge on a circuit came from the sky. The IEC guidance on protecting electronic systems treats lightning and switching transients together, because a large motor dropping off a shared circuit produces its own. A board that failed on a clear evening has not ruled out a supply event.

The board holds the lowest tolerance of anything in an aircon, which puts it first in line. A compressor winding and a fan winding are lengths of insulated wire built for continuous duty. The board runs low-voltage electronics, and what it survives in the way of a brief overvoltage is a fraction of what the motors shrug off.

Protection standards treat that tolerance as the number every other choice is set against. IEC 62305-4 requires the let-through voltage of an installed device to be matched to the immunity withstand voltage of the equipment behind it. The board's own limit is the target: a device earns its place only if it holds the residue below that limit.

The board is also live for far longer than the machine runs. Anything with a receiver listening for the remote draws standby power the whole time the circuit is on, so the board sits energised through storms that pass while the unit is switched off. Exposure follows the circuit, not the running hours.

A damaged board is the most expensive failure short of the compressor. Sourcing for older models is the usual constraint, taken apart in pcb repair vs replacement. How a failing board announces itself is sorted under faulty pcb signs.

Protection is positioned at boundaries, wherever a service crosses from a more exposed zone into a less exposed one. IEC 62305-4 puts it as fitting appropriate devices at every such crossing. The crossings are where the supply enters the building, the distribution board, and the equipment itself.

No single position covers the job, and the standard is blunt about it. A heavy device at the service entrance takes the bulk of the energy, but on its own gives no effective protection against failure of sensitive electronic systems. Downstream devices hold what is left down to something the equipment can survive; the set is described as coordinated, meaning the positions are chosen together.

In a flat, only the last position belongs to the household. The incoming service and the main switchboard of an HDB block or condominium belong to the building, and nothing an owner arranges reaches them. What an owner controls starts at the consumer unit, the db box on the wall.

That leaves a trap worth naming before anybody spends money on it. A plug-in protector guards whatever is plugged into it, and a wall aircon is wired to a dedicated circuit with no plug anywhere in the path. Buying one for a television and assuming the aircon came along is a common and understandable error. The aircon has its own circuit precisely so that it shares nothing.

Anything fitted inside a consumer unit is licensed work, covered under licensed electrical worker. An owner's part of the job is deciding whether to ask the question, never choosing the part.

Every standard in this area speaks of reducing risk; none offers to remove it. SS 555 Part 4 covers protection of electrical and electronic systems, and describes its measures as reducing the risk of permanent failures caused by a lightning electromagnetic impulse. Part 2 sets out a risk assessment procedure, which would have no purpose if no residual risk were assumed.

A device limits, and limiting leaves something behind. What gets through is the let-through voltage, and the design question is whether that remainder falls below what the equipment can take. Where it does not, the device worked correctly and the board failed anyway.

Badly chosen positions can make matters worse. Poor coordination leaves downstream devices absorbing more energy than they were selected for, which risks both the device and the equipment. A protective part never sized for what reached it becomes a hazard inside a switchboard.

A fitted device also has a service life, and is not a permanent alteration to the building. SS 555 Part 4 covers inspection, maintenance and testing alongside design and installation, so the thing has to be looked at again. Installed and forgotten, it is an assumption that stays untested until the next event.

The useful record gets made on the night, and almost none of it survives the week: what was running, what stopped, what carried on, and roughly when. Those four facts tell a supply event apart from a fault that had been building quietly.

Whether other equipment was affected is the most valuable line in that record. Something arriving on the supply reaches the whole circuit, not one appliance. Where the aircon board, a router and a set-top box all went in the same hour, the supply is implicated; where the aircon alone stopped, the case weakens sharply.

There is a public record of lightning, though it is built to look forward. NEA runs a detection system covering cloud-to-ground lightning and lightning inside storm clouds. The myENV app alerts subscribers when detection or a thundery-shower forecast falls within six kilometres of a saved location. An alert is worth keeping, but the service warns rather than archives.

A storm and a dead board on the same evening make a sequence. Turning a sequence into a cause is somebody's job, and nobody can do it from memory alone. Boards give way on quiet nights too, and one already marginal will often pick the night the supply moves.

• •The date, and the nearest hour anyone can name
• •Whether the weather did anything unusual then, and whether an alert came through
• •Which unit stopped, and whether the other units in the flat kept running
• •What else on the same circuit or in the same flat behaved oddly afterwards
• •Whether anything at the db box had moved, and whether anyone reset it
• •Whether the unit was running, switched off at the remote, or off at the wall
• •What the display or indicator lights did immediately after, if anyone saw them