Electrical Load Calculation for House Wiring, Worked for a 2BHK

Electrical load calculation for house: the short answer

An electrical load calculation for a house adds up the rated watts of every appliance and light you will connect, which gives the connected load, then estimates which of them run at the same time, which gives the peak or maximum demand. The connected load tells you how much is wired in. The peak decides the main MCB, the sanctioned load you apply for, and whether single phase is enough.

We work both numbers through for a typical 2BHK below. With three 1.5 ton ACs, two storage geysers and a normal kitchen, the connected load comes to about 15.5 kW, while the realistic peak on a summer evening is about 6.8 kW. The gap between those two figures is why nobody sizes a main switch by adding up everything on the list.

Every wattage here is a typical figure from our appliance power consumption chart, not a measurement of any model; your appliances’ rating plates give the real ones. We make the MCBs, isolators and distribution boxes the result feeds into, at our works in Marol, Andheri East, Mumbai. The final design is a licensed electrician’s job.

What is connected load and how is it calculated?

Connected load is the total of the rated power of every appliance, light and fixed equipment wired into a home, calculated by listing each item with the watts printed on its rating plate, multiplying by how many there are, adding them all, and dividing by 1,000 to express the result in kilowatts.

It counts everything connected, whether or not it runs together: the AC in the guest room that is on ten nights a year counts the same as the fridge that never stops. That is why connected load is always the larger figure.

Where to find the watts: the rating plate, the carton, the BEE star label or the manual. If a plate gives amps instead, multiply by 230 for a single phase appliance. For an AC, use the input watts on the outdoor unit’s plate, not the tonnage.

Typical ranges for every common appliance, from a 9 W LED lamp to a 3,000 W geyser, are in our appliance power consumption chart; we use those figures throughout this page.

How to calculate electrical load step by step

To calculate the electrical load of a house step by step, list every appliance by room, write the watts from each rating plate, multiply by quantity, add them for the connected load, mark which loads run together at your busiest hour, add those for the peak, and divide the peak by 230 to get the current your main MCB must carry.

Step 1 List by room, using your layout plan. Step 2 Watts from each plate. Step 3 Watts × quantity. Step 4 Add all: connected load. Step 5 Pick the busiest hour, often a summer evening or a winter morning. Step 6 Add only what runs then: peak. Step 7 Peak ÷ 230 = amps at single phase.

A spreadsheet with four columns, appliance, watts, quantity and “on at peak?”, does all of it. Our house electrical layout plan gives a worked 2BHK point list to start from.

Keep the list. It is the same list the supply company asks for when you apply for more load, and the one your electrician needs to plan circuits.

Electrical load calculation for a 2BHK: worked example

In our worked 2BHK, with three 1.5 ton ACs, two storage geysers, a full kitchen, a washing machine, a water pump, three ceiling fans and 17 LED light points, the connected load adds up to about 15,468 W, or roughly 15.5 kW, with the ACs and geysers making up more than half of it.

The list, at typical watts: 3 ACs × 1,500 W = 4,500; 2 geysers × 2,000 W = 4,000; induction 2,000, microwave 1,200 and mixer 750 = 3,950; iron 1,000, washing machine 500 and pump 750 = 2,250; fridge 250; 3 fans × 75 W, 17 LED lamps × 9 W, plus TV, laptop and router = 518.

Lights, fans and electronics, the things that run longest, are about 3% of the connected load. Heating and cooling are most of the rest.

How much kW load is needed for a 2BHK?

In our worked 2BHK the peak load is about 6.8 kW, on a summer evening with all three ACs, the fridge, fans, lights and the induction cooktop on together, against a connected load of about 15.5 kW, so the house needs a supply and main switch sized for roughly 7 kW, not 15.

The two busy hours, at typical watts: Evening 3 ACs 4,500 + induction 1,500 + fridge 250 + fans 225 + lights 153 + TV, laptop and router 140 = 6,768 W. Morning 2 geysers 4,000 + induction 1,500 + mixer 750 + fridge 250 + fans and lights about 200 = 6,700 W.

Take the ACs out and the evening drops to about 2.3 kW; the morning, driven by the geysers, barely moves. A 2BHK with fewer ACs or a single geyser lands lower. Your own list, not ours, gives your figure.

Connected load vs maximum demand: why the peak is lower

Maximum demand is lower than connected load because appliances do not all run at once and many cycle on and off: the geyser heats for half an hour, the iron for fifteen minutes, the AC compressor slows once the room is cool, so the highest load actually drawn is a fraction of everything wired in.

In our worked 2BHK, the peak is about 44% of the connected load. That is our example, not a factor to apply to every house. A family that runs two geysers and the washing machine heater together, or three ACs and an induction cooktop at dinner, pushes the peak higher.

Three habits keep the peak down without giving anything up: stagger the geysers, run the washing machine outside the AC hours, and switch the geyser off once the tank is hot. Each of these also helps the bill; our guide to how to calculate an electricity bill turns units into rupees.

Some meters record maximum demand. If your bill shows it, compare that figure with your own estimate: the meter is the better witness.

Sanctioned load vs connected load: which figure do you need?

You need both: connected load is the total you calculate from your appliance list, while sanctioned load is the figure in kW or kVA your supply company has agreed to supply, printed on your bill, and the calculation tells you whether the sanctioned figure still covers how your home actually uses power.

Supply companies differ on how they assess it. Some look at the connected load declared on the application, others at the maximum demand the meter records. Fixed charges in many tariffs depend on the sanctioned figure, so it is worth getting right in both directions.

If your peak estimate sits well above the sanctioned load, for example after adding two ACs, the supply company will usually expect an application to raise it, often with a load list and a test report from a licensed electrical contractor.

What sanctioned load means, where it sits on the bill and kW vs kVA are explained in our single phase vs three phase guide; we have not repeated them here.

From kW to amps: sizing the main MCB

To turn a load in kW into the current the main switch must carry, divide the watts by 230 for a single phase home, so our worked 2BHK’s 6.8 kW peak is about 29 A, which is why a 40A double pole main gives sensible headroom while a 32A one would run close to its limit.

The arithmetic: 6,768 W ÷ 230 V ≈ 29.4 A. Everything on at once would be about 67 A, which no one sizes for. A small flat with lights, fans and a couple of ACs commonly runs on a 32A or 40A incomer; a larger home moves to 63A, as our which MCB for home guide sets out.

VIYONA 412 is a 40 A double pole 10 kA MCB at ₹435 MRP. An isolator can be the main only where every circuit below has its own MCB.

Load per circuit: checking each MCB

Load per circuit is the sum of what each circuit carries at its busiest, and it decides that circuit’s MCB and wire: each AC and each geyser gets its own circuit, so one appliance’s current sits on one MCB, while lights, fans and general sockets are split over a few circuits so none runs near its limit.

In the worked 2BHK, that means about ten outgoing circuits: two for lights and fans, two for general sockets, one for the kitchen’s heavy points, three for the ACs and two for the geysers, plus two spare ways on a 12 way board. Our layout guide draws the same split.

Check each circuit the same way as the house: add its loads, divide by 230, and compare with the MCB. A kitchen circuit carrying the induction (2,000 W), microwave (1,200 W) and mixer (750 W) together reaches about 17 A, more than a 16A circuit should carry; electricians commonly split such loads.

Matching the wire to each MCB is in which wire for AC and geyser; the box size for the circuit count is in our MCB box size list.

Single phase or three phase: when the load decides

The load calculation decides single vs three phase when the peak current on one phase gets uncomfortably large, as it does in homes with several ACs, an instant geyser or a three phase motor, or when the supply company’s rules ask for three phase above a load limit in its supply code.

Our worked 2BHK, at about 29 A peak, is a comfortable single phase home. Add a fourth AC and an instant geyser and the peak can pass 45 A, which is where an electrician starts discussing a three phase connection or a higher single phase incomer.

In a three phase home the same list is split across the R, Y and B phases, ideally one AC per phase, so each phase carries about a third. The three phase board needs a four pole main: our VIYONA 461 four pole isolator is ₹480 MRP and the 432 four pole MCB ₹855.

When it is worth switching, and how loads are balanced, is covered in single phase vs three phase.

Adding an AC, geyser or EV charger: recalculate first

Before adding an AC, a geyser, an induction cooktop or an EV charger, rerun the load calculation, because each one adds kilowatts to the peak, needs its own circuit, MCB and wire, may need a spare way in the board, and can push the total past your sanctioned load or your main MCB’s rating.

One more 1.5 ton AC adds about 1.5 kW to a summer evening, roughly 6.5 A. In the worked 2BHK that takes the evening from about 29 A to about 36 A, past a 32A main and still inside a 40A one.

An EV charger is a long, heavy load that may run for hours overnight; its maker specifies the circuit, and the electrician checks it against the sanctioned load. Backup circuits for an inverter change the picture too; see inverter for home.

If the board has no spare way, a new appliance means a bigger box. Our VIYONA SPN white line box runs from ₹380 for 2–4 way to ₹950 for 16–18 way.

Common load calculation mistakes

The commonest load calculation mistakes are adding up MCB ratings instead of appliance watts, using AC tonnage as if it were kilowatts, forgetting the geysers and the washing machine heater, sizing the main for the connected load instead of the peak, and never redoing the sum when a heavy appliance is added.

Adding MCB ratings Ten MCBs of 16A do not mean 160 A of load. Tonnage as kW A 1.5 ton AC is not 1.5 kW by definition; read its plate. Forgotten heaters Geysers and washing machine heaters set the morning peak. Connected = peak Oversizes the main and the application. One-time sum A house’s load grows; the calculation should too.

A careful list also shows where the cheap savings are. Our worked example’s lights and fans are a sliver of the load; the geysers and ACs are where timing and settings matter.

For the cost of wiring a home sized this way, see our guide to house wiring cost.