Electrical Load Calculation for Buildings in Pune: Connected Load, Maximum Demand, Transformer and DG Sizing

Why the load calculation comes first

The electrical load calculation is usually the first MEP document a building needs. It decides the size of the transformer and where its room goes, the size of the DG set and the weight the structure must carry for it, the number of meters and the size of the meter rooms, and the load applied for from the electricity supply company. All of those have to be on the architect's plans long before the electrical layouts are drawn.

It is also the document that changes most often. Every added floor, every change of use and every new EV charging requirement moves the load, so we keep the calculation as a working sheet and reissue it with each revision of the plans.

Step 1: the connected load

The connected load is the sum of everything that can draw power in the building. On residential projects in Pune we build it up from:

• Every flat at 75 W per sq m of carpet area, and shops and offices at a higher rate - 150 W per sq m on our Punawale towers
• Lifts, by motor rating: on the Ravet tower, five 15 HP lifts
• Pumps: domestic, drinking water, flushing, booster, sewage, sump and dewatering pumps, and the fire pumps
• Basement ventilation and staircase and lift-well pressurisation fans
• Common, street and landscape lighting
• The sewage plant, the water treatment plant and the organic waste converter
• EV charging, usually for 20 to 30% of the parking, at 7.2 kW for a car and 3.5 kW for a two-wheeler
• Amenities: the clubhouse, a recreation floor or a gym

Step 2: from connected load to transformer

Not everything runs at once, so the connected load is reduced by a diversity factor to the maximum demand - the most the building is expected to draw at one time. The maximum demand in kW is converted to kVA at a power factor of 0.9, and a 20% margin is added before the transformer is chosen. On the Ravet tower, the steps look like this:

Figures from our projects

On housing, the maximum demand comes out at roughly half the connected load: 941 of 1,898 kW at Ravet, 332 of 673 kW at Balewadi. The same steps on buildings of different sizes:

EV charging is now one of the largest loads

Charging for a share of the parking is now asked for on almost every housing project we design, and it changes the load more than any other single item. On the Kiwale towers, 158 charging points add 755 kW, almost a third of the connected load. On the Bhukum township, 144 car chargers of 7.2 kW add 1,035 kW - the second-largest load after the homes. On the Mantra towers at Balewadi, charging for 30% of the bays - 303 car points, 10 fast DC chargers and 87 two-wheeler points - comes to 1,795 kW connected.

If charging is added after the transformer is sized, the transformer room is usually too small for the change, so we put it in the first calculation.

Sizing the DG set

On housing, the DG set does not carry the whole building. It carries the services that must keep running in a power cut - the lifts, the pumps, the ventilation and pressurisation fans and the common lighting - with its own diversity factor, and it is checked against the starting current of the largest motors, because a lift starting draws far more than it runs at.

The DG set and the structure

A DG set is heavy, and it is often placed on a podium or above another room. On the Khindwadi project at Satara, the 160 kVA set sits above the transformer room, so its 3-tonne dead weight went to the structural engineer with the layout.

Meters and supply to each flat

The load calculation also sets the number of meter connections, which decides the size of the meter rooms and panels. The Punawale tower has 78 connections - 71 single-phase flats, 4 three-phase shops and 3 common supplies. On the Balewadi building, every flat has a three-phase supply, and the 68 connections are grouped floor by floor on four meter panels. In the Chinchwad office building, 9 of the 38 meters are CT meters for the larger offices and the restaurant.

Hospitals and factories

Outside housing, the diversity is lower, because more of the load runs at the same time. On the Chakan industrial shed, 623 high-bay lights, 700 fans, the offices and the production machinery come to 466 kW connected and 405 kW of maximum demand, which sets a 630 kVA transformer and a 625 kVA DG set.

On the Super Nova hospital at Kalyan, the clinical equipment alone - a cath lab of 80 kW, two operating theatres, X-ray, 17 ventilators, sterilisation and laser - is 171 kW of the 427.8 kW connected. The load statement was reissued seven times as the equipment list grew, ending at 259.3 kW of maximum demand, 288 kVA on a 500 kVA transformer, with the emergency boards kept on their own circuits for the standby supply.

What to send

To prepare the electrical load calculation for your building, we need:

• The area statement with the carpet area of every flat, shop and office
• The architectural plans and sections, with the number of floors and basements
• The number of lifts and parking bays, and the share of bays that need EV charging
• The amenities and any special loads: a clubhouse, a pool, a kitchen, or production or medical equipment
• Any requirement from the supply company or the environmental consultant, if you already have it

Our electrical design work

We prepare load calculations as part of the full MEPF design for housing, offices, hospitals, schools and factories across Pune and Pimpri-Chinchwad, and the same figures feed the environmental clearance data and the fire pump power supply. See MEP consultants in Pune, or send your drawings for a free project review.