Your DB has three live busbars — Red, Yellow, Blue — 400V between any two of them, 230V between each and neutral. Here's what that actually buys you, why it's split across your circuits, and what happens when it isn't shared evenly.
Instantaneous power in an AC circuit is p(t) = v(t)×i(t). For a single sine wave, that product touches zero twice every cycle — 100 times a second on our 50Hz supply. A single-phase motor genuinely gets zero torque, twice per cycle; it only keeps spinning because of mechanical flywheel effect. Add two more sine waves, each shifted 120°, and sum them — the pulses fill each other's gaps and the total becomes a flat, constant line.
Single phase: power (white) oscillates from zero to peak and back, twice per cycle. Anything driven by it — a motor, a compressor — pulses with it.
That's the core reason the grid runs three phases rather than one: it's the smallest number of shifted sine waves whose sum is perfectly constant. Two phases 180° apart still cancel to a pulsing sum with dead spots; three phases 120° apart is the minimum for a flat total. It also turns out to be a sweet spot for copper: three phases sharing one neutral deliver roughly three times the power of a single circuit using only about 1.5× the conductor, because a fourth phase would need proportionally more conductor for diminishing returns. Six-phase and higher schemes exist (used on some long transmission lines), but for generation and distribution, three has won out worldwide for over a century.
The supply arrives at your meter as four (or five) wires: R, Y, B, Neutral, and Earth — 230V from any phase to neutral, 400V phase-to-phase. Inside the main distribution board (DB), each MCB-protected circuit is wired to one phase and shares the common neutral. A large 3-phase load — a borewell pump, a lift motor, sometimes the main AC compressor — is the exception: it's wired across all three phases at once, because 3-phase motors are simpler, smaller, and don't need a starting-torque trick the way single-phase motors do.
R / Y / B / Black-Neutral / Green-Earth is the classic Indian colour code under IS 732:2019 (older IS 694 wiring still uses it almost everywhere in practice). Newer IEC-harmonised jobs use Brown / Black / Grey for the phases instead — same idea, different colours, so always test before assuming.
This split is exactly why "which phase is my AC on?" is a real, answerable question in an Indian home, and why a good electrician labels the DB by phase rather than just by room.
Because R, Y and B are 120° apart, the current flowing back through the shared neutral isn't the sum of the three phase currents — it's their vector sum. If all three phases draw exactly equal current, the three vectors cancel perfectly and neutral current is zero. The neutral, in a perfectly balanced 3-phase home, is carrying nothing at all. The moment one phase draws more than the others, that cancellation breaks and the leftover current has to flow somewhere — through the neutral conductor.
Drag any one phase up and leave the other two low — a big AC or a heater sitting alone on Yellow, say — and watch the neutral phasor (grey, centre) grow instead of collapsing to a point. That grey arrow is real current your neutral wire now has to carry, even though nothing was "supposed" to flow there.
You're right to push on this: the simulator above balances instantaneous current, but a home isn't instantaneous — lighting peaks in the evening, a geyser peaks for twenty minutes in the morning, bedroom ACs run overnight. Spreading total connected watts evenly across R/Y/B is the wrong target, because those totals are never all live at once. The real target is coincident current — what's actually drawn on each phase during the same clock-hour — and that depends on when things run, not just how big they are.
The practical method is just four steps:
| Circuit | ~Current | Typically runs | Phase |
|---|---|---|---|
| Geyser / water heater | 7 A | Morning, 6–8am (brief) | R |
| Living room AC | 6 A | Day & evening, 12pm–11pm | Y |
| Bedroom AC | 5 A | Night, 10pm–6am | B |
| Kitchen sockets / mixer | 3 A | Morning + evening bursts | B |
| Whole-home lighting | 2 A | Evening–night, 6–11pm | R |
| Fridge (cycling) | ~1.5 A avg | Continuous | Y |
| Router / CCTV / standby | 1 A | Continuous | R |
| Borewell pump | 8 A | Brief, ~20 min/day | R+Y+B |
| Morning | Day | Evening | Night | |
|---|---|---|---|---|
| R | 8.0 A | 1.0 A | 3.0 A | 1.0 A |
| Y | 1.5 A | 7.5 A | 7.5 A | 1.5 A |
| B | 3.0 A | 0 A | 3.0 A | 5.0 A |
Read this by column, not by row: no single phase dominates every time-of-day the way it would if all the heavy loads had been dumped onto one phase. R takes the morning spike, Y takes the day and evening AC load, B takes the night. The neutral only ever has to carry the difference between phases within a given hour — never the full sum of everything in the house.
Notice Day mode: Y carries most of it and B carries almost nothing, because the living-room AC is genuinely the only big daytime load in this home — there's nothing to balance it against. That's normal, and it's fine. Perfect three-way balance in every single hour isn't the goal or even achievable in a real home; the goal is making sure your biggest recurring loads — the ones that run for hours, not minutes — don't all land on the same phase. A 20-minute pump cycle or a morning geyser spike matters far less than which phase carries the AC that runs for six hours straight.
The neutral conductor is often sized like a single phase, on the assumption it will rarely carry much. A chronically unbalanced home pushes real current through it continuously — extra I²R heating, in a wire nobody's watching because it isn't behind its own MCB.
An unbalanced load pulls the "star point" off-centre: the heavily loaded phase sags a little, the lightly loaded one creeps up above 230V. Bulbs on the light phase run hot and die early; appliances on the heavy phase brown out under peak draw.
If the shared neutral connection loosens or fails entirely (a known failure mode at old junctions and meter boxes), the three phases lose their common reference. The lightly-loaded phase can then float up toward the 400V line‑to‑line value instead of 230 — enough to destroy electronics and appliances on that phase almost instantly. This is the single most common cause of "half the house's gadgets died at once" incidents.
Even short of failure, an unbalanced system simply wastes capacity: the transformer and service cable are sized for a given total current, and unbalance forces derating — you get less usable power from the same sanctioned load, plus higher I²R losses across the whole run.
Motors, pumps, fans, and AC compressors are inductive loads — their current lags the voltage by some angle φ, because energy is briefly being stored in a magnetic field and handed back, cycle after cycle. That lag means the current you draw is larger than what's strictly needed to deliver the real, working power (kW). The ratio between them is the power factor, cosφ — 1.0 for a purely resistive load like a heater or incandescent bulb, typically 0.6–0.85 for an uncorrected motor or pump.
Notice the important part: real power (the chip on the left) barely moves as you drag φ up — the appliance is still doing roughly the same useful work. But the current your wiring has to carry keeps climbing. That extra current doesn't run the fan any faster; it just sits in the conductors as heat and voltage drop. A borewell pump or old-style tube-light choke with poor power factor draws meaningfully more current — and heats its own wiring more — than its kW rating alone would suggest.
Domestic LT tariffs in India don't usually bill power factor directly the way commercial/industrial connections do, so this rarely shows up on your bill line-item. It still matters locally: it's extra heat in your DB and cabling, extra voltage drop on long pump-motor runs, and it's exactly why 3-phase motor starters and larger pump installations are commonly fitted with a capacitor bank to pull cosφ back up toward 0.95–1.0.
The same logic scales up directly: sizing a load sanction for something like a multi-court facility (lighting banks, a borewell motor, refrigeration) is the same balancing exercise with bigger numbers — spread the fixed loads across R/Y/B from the design stage, and the motor loads are where power factor correction actually starts to matter.