Connected load, MD, demand factor, load factor

These four terms describe how the electrical capacity of an installation is used. A single example plant is used to show each.

Example plant: 6 motors of 15 kW, furnace 30 kW, lighting 10 kW.

Connected load

The sum of the rated (nameplate) powers of all equipment connected to the supply. It is the maximum the plant could draw if everything ran at full load together.

Connected load = 6×15 + 30 + 10 = 130 kW

Maximum demand

The greatest load drawn during a period, measured as the highest average over a short interval (15 or 30 minutes) by an MD meter. Since machines run below rating and not all together, MD is less than the connected load. It decides the size of transformer, cables and switchgear, and the demand charge on the bill.

Maximum demand recorded = 78 kW

Demand factor

The ratio of maximum demand to connected load. It is always ≤ 1 and is used to estimate MD at the design stage.

Demand factor = 78 / 130 = 0.6

Typical values: motors 0.6–0.8, lighting about 1.

Load factor

The ratio of average load to maximum demand over a period (day, month, year). It shows how steadily the plant uses power.

Energy used in a day = 936 kWh
Average load = 936 / 24 = 39 kW
Load factor  = 39 / 78 = 0.5

A high load factor means equipment is used well and the cost per unit of energy is low. Running some loads (pumps, furnaces) in off-peak hours raises the load factor.