Commercial load calculation — what the feeder actually carries

PILONE CABLES TECHNICAL TEAM

Add up every rated watt on the panel for the connected load, apply a diversity allowance group by group for the maximum demand, then divide by the power factor for kVA. The worked commercial unit below runs 35.7 kW connected to 26.8 kW of demand, 31.5 kVA, and 45.5 A per phase on a 400 V three-phase supply.

Nothing on a commercial panel runs flat out in the same second, so a feeder sized to the connected load buys copper that never carries current. This page stops at the amps, which is where the load calculation ends; the conductor that carries them is picked off the chart on 3-phase cable size.

Connected load and maximum demand are two different numbers

Connected load is the arithmetic sum of every rated watt installed on the panel. Maximum demand is the largest load that panel will actually carry at one moment, and on any commercial installation it is the smaller of the two. The gap between them is the diversity allowance, applied group by group rather than as one blanket percentage, because shop lighting behaves nothing like a geyser. Size a commercial feeder to the maximum demand with a stated spare margin on top — sizing to an average leaves nothing for the summer peak.

The inputs come off rating plates, not off a chart. Walk the unit with the equipment list and write down what each plate says. Where a plate is missing or the equipment has not arrived, a typical figure is a placeholder to be replaced — and the one number worth chasing hardest is the air conditioning, because on a Pakistani shop or office it is usually close to half the total on its own.

One thing a maximum demand calculation is not. It is not the sanctioned load on your meter — that is the figure the utility sets when the connection is applied for, and it governs what you may draw, not what your cable must carry.

A worked load schedule for a commercial unit

Take a real shape of building: 2,000 sq ft of retail floor on the ground with a 1,000 sq ft office above it, on a three-phase connection. Count the items, multiply by the plate rating, and total the column.

Connected load for a 3,000 sq ft retail-and-office unit. Ratings are typical figures for planning — read your own plates and replace them. The socket and signage rows are per-outlet allowances, not nameplate readings, and are marked as such. Verify the finished schedule with a licensed electrician before it is used to size anything.
Load group	Qty	Typical rating each	Connected
LED tube and panel lighting	60	40 W	2,400 W
Ceiling fans	12	80 W	960 W
Split AC, 1.5 ton	6	1,800 W	10,800 W
Split AC, 2 ton	2	2,400 W	4,800 W
Display chillers and refrigeration	3	1,500 W	4,500 W
Computers, POS terminals, printers	12	300 W	3,600 W
General socket outlets (allowance)	20	200 W	4,000 W
Electric geyser	1	2,000 W	2,000 W
Signage and display lighting (allowance)	—	1,500 W	1,500 W
Water pump, about 1.5 HP	1	1,100 W	1,100 W
Connected load	—	—	35,660 W = 35.7 kW

One cross-check before going further: 35,660 W spread over 3,000 sq ft is 11.9 W per sq ft. Run the same division on your own schedule. A retail-and-office figure far below that usually means a load group was missed; far above it usually means a plate rating was read as a running figure when it was a maximum.

The diversity factor, applied group by group

A diversity factor is the fraction of a group's connected load that is drawing current at the same moment. Shop lighting sits at 1.0 because it is all on from opening to closing. Air conditioning sits below it because compressors cycle. A geyser and a pump sit well below, because each runs for minutes in an hour. One blanket percentage across the whole panel hides all of that, which is why the allowance is applied per group and then totalled.

Maximum demand from the schedule above. The allowance column holds this page's worked assumptions, published so the arithmetic can be audited — they are not values quoted from a standard. Use your own metered data, or the figures your consultant works to. Verify with a licensed electrician for your installation.
Load group	Connected	Allowance	Demand
Lighting	2.40 kW	1.00	2.40 kW
Ceiling fans	0.96 kW	1.00	0.96 kW
Air conditioning	15.60 kW	0.80	12.48 kW
Refrigeration	4.50 kW	0.80	3.60 kW
Computers and POS	3.60 kW	0.75	2.70 kW
General sockets	4.00 kW	0.40	1.60 kW
Geyser	2.00 kW	0.50	1.00 kW
Signage	1.50 kW	1.00	1.50 kW
Water pump	1.10 kW	0.50	0.55 kW
Maximum demand	35.66 kW	0.75 overall	26.79 kW

The overall figure falls out of the working rather than being chosen: 26.79 ÷ 35.66 = 0.75. That is the number worth writing on the drawing, because it is the one a reviewer will challenge. An allowance quoted with no schedule behind it cannot be checked by anybody, including the person who wrote it.

From kW to kVA to the amps on the feeder

Cable carries current, not kilowatts, so the demand has to be converted. Three steps, all short.

1. kW to kVA

Divide the demand by the power factor. 26.79 ÷ 0.85 = 31.5 kVA. That is the figure a transformer or a generator is rated in.

2. kVA to amps

Amps = kVA × 1000 ÷ (√3 × 400). The denominator is 1.732 × 400 = 692.8, so 31,500 ÷ 692.8 = 45.5 A per phase.

3. Add the spare margin

Take 25% on top before sizing anything: 45.5 × 1.25 = 56.9 A. Design current 57 A, not 45.5 A.

Worth seeing what three phases buy. The same 26.79 kW on a 220 V single-phase supply would be 26,790 ÷ (220 × 0.85) = 143 A, which is not a shop connection — it is the reason a unit of this size is given three phases in the first place. Plant and building drawings in Pakistan often write the supply as 415 V rather than 400 V; the arithmetic here uses 400 V, which returns the higher current for the same kW and therefore the safer answer.

57 A of design current is where this calculation hands over. Take that figure, the one-way run length and the ambient the cable will sit in to the 3-phase cable size chart, which converts kW and amps into mm²; the feeder sizes we draw most often for loads of this order are listed under all standard cable sizes.

What moves the answer

Power factor, more than most people expect. 0.85 is the assumption used above. At 0.80 the same 26.79 kW draws 26,790 ÷ (692.8 × 0.80) = 48.3 A instead of 45.5 A — about 6% more current for no extra work done. A floor full of motors and old fluorescent gear sits lower; correction gear pulls it back up.
Phase balance. The single-phase circuits are split across the three phases, but never evenly. The feeder is sized on the worst-loaded phase, not on the average of the three, so total each phase separately before converting to amps.
The run. Past roughly 100 m it is voltage drop, not current, that picks the conductor, and a load calculation cannot see that. Check the length in the voltage drop calculator once you have a candidate size.

Every allowance on this page is a stated worked assumption, not a value taken from a standard, and every current figure depends on the power factor and phase balance of your own installation. A commercial feeder is not a job to size from a rule of thumb: have a licensed electrician confirm the load schedule, the diversity across circuits and the final cable size before the panel is wired. For a single circuit — one AC, one motor, one appliance — the cable size calculator gives a faster answer.

Frequently asked

How do you calculate the maximum demand for a commercial building?

List every load with its rated watts and total them — that is the connected load. Apply a diversity allowance to each group, because shop lighting runs all day while a geyser runs for minutes, and total again. That second figure is the maximum demand. Divide it by the power factor for kVA, then convert to amps. The worked unit here runs 35.7 kW connected to 26.8 kW of demand.

What is a diversity factor, and what value should I use?

It is the fraction of a group's installed watts drawing current at the same moment. Air conditioning cycles, so it sits below 1.0; shop lighting is on from opening to closing, so it sits at 1.0. Take your values from your own metered data or from the figures your consultant works to. The allowances on this page are worked assumptions, published so the arithmetic can be audited.

Commercial connection ke liye load kaise nikalte hain?

Pehle har cheez ki plate par likhi watt jama karein — yeh connected load hai. Phir har group par diversity lagayein, kyunke AC, geyser aur socket ek hi waqt mein poore nahin chalte. Jo figure bachta hai woh maximum demand hai. Usse power factor par taqseem karein to kVA milta hai, aur 400 volt three-phase par amps nikal aate hain.

Is connected load the same as the sanctioned load on the meter?

No. That is your own arithmetic, the sum of the rated watts you install. The sanctioned load is what the utility sets on the connection when it is applied for, and it governs what you may draw rather than what your cable must carry. Size the feeder to your calculated demand with spare capacity, and raise the sanctioned load separately if that demand outgrows it.

How do I turn kW into amps on a 400V three-phase supply?

Amps = kW × 1000 ÷ (1.732 × 400 × power factor), where 1.732 is the root of three. At a power factor of 0.85 the denominator comes to 588.9, so a 26.8 kW demand is 45.5 A per phase. Pakistani drawings often write the supply as 415 V, which returns a slightly lower current for the same kW. The mm² that carries those amps is chosen on the 3-phase cable size page.

How much spare capacity should a commercial feeder have?

Add 20 to 25 percent to the demand figure and size to that. On the worked unit here, 45.5 A becomes about 57 A of design current. Tenants add loads — a second chiller, another AC, a bigger sign — and the feeder is the one run nobody wants to pull twice. Spare capacity is far cheaper bought as copper than as a second cable.

Send the load schedule, get the feeder priced

We draw the copper in Lahore and sell it at the day's rate — no dealer margin. Send the equipment list or the bill of quantities with the run length and your city: Punjab in 1–2 days, rest of Pakistan in 2–4.

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