Demand factor: the share of load that is actually used
Every installation is described by two very different numbers: the load that could be connected, and the load that is actually drawn at the busiest moment. The demand factor links them. It is the ratio of maximum demand to connected load, and because no building switches everything on at once, the ratio is normally well below one.
Connected load is the sum of every load's rated input — heaters, motors, lighting, socket outlets and so on. Maximum demand is the highest power the installation is expected to take over a defined period. A building with 100 kW connected and a demand factor of 0.6 only needs a supply sized for 60 kW.
Demand factors are not fixed. They depend on the mix of loads and how the building is used: a block of flats behaves differently from a workshop, and a workshop differently from an office. Standards and national wiring rules publish typical values, but the engineer still has to judge whether a particular project really fits the tabulated case.
Diversity factor: how peaks spread across a system
Diversity factor asks a different question. Instead of comparing demand with connected load, it compares the sum of the individual maximum demands of the separate parts with the maximum demand of the whole. Because the parts do not peak at the same instant, the whole is smaller than the sum of its parts, and the ratio is greater than one.
Consider four sub-distribution boards whose individual maximum demands are 50 A, 40 A, 30 A and 20 A. The arithmetic sum is 140 A, yet the main incomer may never see more than 100 A. The diversity factor is 140 / 100 = 1.4, and that single number tells you how much the peaks overlap in practice.
Diversity is what lets a designer size a main switchboard, a rising main or a transformer smaller than the arithmetic total of every downstream board. Ignore it and the supply is oversized and wasteful; over-apply it and the supply may trip at the worst possible moment.
The difference between the two factors
The names are often used loosely, so it is worth keeping them apart. The table below sets out the working difference.
| Aspect | Demand factor | Diversity factor |
|---|---|---|
| Compared | Maximum demand to connected load | Sum of part demands to whole demand |
| Typical range | Below 1 | Above 1 |
| Applied to | A single load group or board | A system of several boards |
| Answers | How much of the load is used | How much the peaks overlap |
| Mainly affects | Feeder and board sizing | Upstream mains and transformers |
In practice both are used in sequence. Demand factors turn connected load into realistic demands at each board; diversity factors then combine those demands into one figure for the supply.
Where the numbers come from
Most values come from three sources, and a sound calculation uses all of them.
- Published tables in standards and wiring rules, which give typical factors for dwellings, offices, shops and light industry.
- Manufacturer data for large single loads, where the duty cycle of a motor, lift or chiller sets the real demand.
- Project experience and metered records, which show how the building is likely to be operated rather than how it was designed.
A common error is to treat a tabulated value as exact. The factor is a planning assumption, and on an unusual project a short conversation with the client about operating patterns is worth more than a table row.
A worked example
Take a small building with three final distribution boards, each with its own connected load and demand factor.
- Board A: 40 kW connected, demand factor 0.7, giving 28 kW.
- Board B: 30 kW connected, demand factor 0.6, giving 18 kW.
- Board C: 20 kW connected, demand factor 0.8, giving 16 kW.
The sum of the three demands is 28 + 18 + 16 = 62 kW. Applying a diversity factor of 1.24 across the group, the maximum demand at the incomer is 62 / 1.24, which is about 50 kW.
The supply is therefore sized for roughly 50 kW rather than the 90 kW of connected load. The figures are illustrative, but the sequence — demand first, diversity second — is the one used on real projects.
Common mistakes and practical limits
A handful of habits cause most of the errors in applied load calculations.
- Using one demand factor for an entire building instead of assessing it by load group.
- Applying diversity inside a single final circuit, where every load on the circuit is genuinely simultaneous.
- Applying diversity twice along the same chain, and so underestimating the supply.
- Mixing kW and kVA without allowing for power factor, which distorts currents and cable sizes.
- Reusing an old factor set on a project whose load mix has changed beyond recognition.
Keeping the assumptions in writing, next to the calculation, is the simplest protection. A reviewer should be able to see which factors were chosen and why.
Handling the factors in GorkyCAD
GorkyCAD treats demand and diversity as part of the electrical model rather than as a separate spreadsheet. Loads, boards and feeds are drawn once, and the totals follow from that single source. The toolset includes a broad set of load and fault calculations and checks against IEC 60364, so the numbers you review are the ones that also drive the panels and cable schedule.
Because sizing decisions upstream depend on the factors chosen downstream, keeping them in one model makes it far easier to see the effect of a change. Adjust a factor at a board and the load seen by the incomer updates with it, instead of being re-keyed somewhere else.
Next steps
Demand and diversity factors are planning tools, not exact physics. Used carefully, they match a supply to the way a building actually behaves; used carelessly, they either waste money or create a nuisance-tripping installation.
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FAQ
Is the demand factor always below one?
Normally yes, because not every connected load runs at full power at the same time. It is a planning ratio rather than a fixed law, so unusual duty cycles should be assessed individually.
Can demand and diversity factors be used together?
Yes, and they usually are. Demand factors turn connected load into realistic board demands, then diversity factors combine those demands into a single figure for the incoming supply.
Where do I find typical factor values?
In national wiring rules and standards tables, in manufacturer data for large loads, and in metered records from similar buildings. A tabulated value should still be checked against the actual project.
Why not simply add up every load?
Adding everything gives the connected load, which is almost always larger than the real maximum demand. Sizing the supply for it wastes capacity, so factors bring the figure back to a realistic value.