Connected Load and Demand Load Calculator
How the formula works
Not all connected loads run at full power at the same time. The calculator reduces the connected load with demand factors and a diversity factor to find the real maximum demand.
Formulas
Demand of a load = Connected load × Demand factor
Sum of demands = Total of all load demands
Maximum demand = Sum of demands / Diversity factor
Design demand = Maximum demand × (1 + Growth %)
kVA = kW / Power factor
Current (three phase) = kVA × 1000 / (√3 × V)
Current (single phase) = kVA × 1000 / V
Overall demand factor = Maximum demand / Connected load
Where:
- Demand factor = maximum demand of one load divided by its connected load (0 to 1)
- Diversity factor = sum of individual maximum demands divided by the maximum demand of the whole group (1 or more)
- Connected load = total rating of all equipment that can be connected
Typical values
Demand factor: lighting 0.8, fans 0.9, sockets and small power 0.5, air conditioning 0.8, motors and pumps 0.75, other loads 0.6. Diversity factor: 1.0 for a single load, 1.1 to 1.3 for a mixed building and up to 1.5 for large groups. Standard transformer sizes used: 25, 40, 63, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000 and 2500 kVA. These are typical planning values. Demand factors depend on the building type and the local code (for example NEC or IS rules). Use your own values where the code gives them.
How to use the calculator: enter the connected load of each group in kW, change the demand factor if you have your own, select the diversity factor, power factor and supply, then click Calculate.
Important notes: do not apply the diversity factor twice. If your demand factors already include diversity, select a diversity factor of 1.0.
Worked example
Example 1: Commercial building
Lighting 20 kW, fans 5 kW, sockets 30 kW, air conditioning 100 kW, motors 40 kW. Typical demand factors, diversity 1.2, power factor 0.9, growth 20 %, three phase 415 V.
Connected load = 195 kW. Demands = 16 + 4.5 + 15 + 80 + 30 = 145.5 kW. Maximum demand = 145.5 / 1.2 = 121.25 kW. With growth = 145.5 kW. kVA = 161.67. Current = 224.9 A. Standard size: 200 kVA (81 % loaded).
Example 2: Residential block
Lighting 10 kW, fans 6 kW, sockets 40 kW, air conditioning 60 kW, motors 7.5 kW, other 5 kW with demand factor 0.5. Diversity 1.5, power factor 0.95, no growth.
Connected load = 128.5 kW. Sum of demands = 89.53 kW. Maximum demand = 59.68 kW. kVA = 62.82. Current = 87.4 A. Standard size: 63 kVA (100 % loaded, so check for growth).
Example 3: Small office, single phase
Lighting 3 kW, sockets 6 kW, air conditioning 9 kW with demand factor 1.0. Diversity 1.0, power factor 0.85, growth 10 %, 230 V.
Sum of demands = 2.4 + 3 + 9 = 14.4 kW. With growth = 15.84 kW. kVA = 18.64. Current = 81.0 A. Standard size: 25 kVA.
Example 4: Small factory
Lighting 15 kW, air conditioning 30 kW, motors 250 kW with demand factor 0.7, other 40 kW. Diversity 1.3, power factor 0.85, growth 25 %, three phase 415 V.
Connected load = 335 kW. Sum of demands = 235 kW. Maximum demand = 180.77 kW. With growth = 225.96 kW. kVA = 265.84. Current = 369.8 A. Standard size: 315 kVA.
Common mistakes
- Using the connected load as the demand load, which gives an oversized transformer or generator.
- Applying the diversity factor twice, once inside the demand factors and again here.
- Writing the diversity factor as a number below 1. It is 1 or more.
- Using the same demand factor for all loads.
- Forgetting standby loads such as a spare pump, which should not be counted in the demand.
- Leaving out the largest motor starting current when sizing a generator.
- Using the power factor of one load for the whole building.
- Not allowing for future growth.
- Counting fire pumps and other emergency loads in the normal maximum demand.
Frequently asked questions
What is connected load?
It is the total rating of all electrical equipment that can be connected to the supply.
What is demand load?
It is the actual maximum load drawn from the supply, usually lower than the connected load.
What is the demand factor?
It is the maximum demand divided by the connected load. It is 1 or less.
What is the diversity factor?
It is the sum of the individual maximum demands divided by the maximum demand of the whole group. It is 1 or more.
What is the difference between demand factor and diversity factor?
Demand factor applies to one load. Diversity factor applies to a group of loads that do not peak at the same time.
How do I calculate maximum demand?
Multiply each connected load by its demand factor, add them, and divide by the diversity factor.
What demand factor should I use for lighting?
About 0.8 is typical, but some codes give a different value for each building type.
How do I find the transformer size?
Divide the maximum demand in kW by the power factor to get kVA, add growth, then choose the next standard transformer size.
What load factor should I keep on a transformer?
Many designs keep the maximum loading at 70 to 80 % to allow for growth and heat.
Can I use this for generator sizing?
It gives the running demand. A generator must also be checked for the largest motor starting current.
How do I size the cable for this current?
Use the Cable Size Calculator with the design current from this page.
Is this a final design value?
No. It is an estimate. Final design should follow the local code and a full load schedule.