Single phase or three phase? It decides how big your solar system can legally be.

Open your meter box and count the thick incoming cables at the main breaker. Single phase has one live and one neutral. Three phase has three lives plus a neutral. The main breaker itself is usually stamped 1P or SP for single phase, and 3P or TP for three phase. Most Malaysian terrace and link houses are single phase. Bungalows, larger semi-detached homes and anything with a lift, a pool pump or several air-conditioners are more often three phase. If you are unsure, photograph the meter box and send it to us — it takes about ten seconds to read.

Under Solar ATAP section 8.1 a domestic single phase supply is capped at a 5 kWac inverter. In practical terms that is around 6.82 kWp of panels. Three phase domestic is capped at 15 kWac. The limit is on the inverter rating in kWac, not on the panel capacity in kWp, which is why a 6.82 kWp system fits inside a 5 kWac cap.

Yes, but not automatically. Going above 5 kWac on a domestic single phase supply requires a Connection Confirmation Check from TNB, which costs RM1,000 and adds waiting time to your application. For most homes it is cheaper and faster to size the system to 6.82 kWp, or to upgrade the supply to three phase if the bill genuinely justifies it.

kWp measures the panels; kWac measures what the inverter can push into your wiring. The grid connection cares about the second number, because that is what actually flows through your supply. A 6.82 kWp array paired with a 5 kWac inverter is compliant even though the panel figure is higher, because the panels rarely produce their full rated output at the same moment.

Only if your electricity use justifies it independently. A three phase upgrade is a TNB application with its own cost and lead time, and on a bill under roughly RM500 a month a 6.82 kWp single phase system will already generate more than most households can self-consume. Under Solar ATAP any surplus you export is credited at a lower rate than the power you avoid buying, and unused credit is forfeited at the end of each billing period — so a larger system on a modest bill can cost more without saving more.

Indirectly. The phase caps the system size, and the system size caps the generation. But what decides your actual saving is how much of that generation you use during the day rather than export. A three phase house that is empty from 8am to 6pm can easily save less per ringgit spent than a single phase house where someone is home.