What is diversity in an electrical installation?

Diversity recognises that not every load in an installation runs at full power at the same time. Applying an allowance to each type of circuit gives an assessed maximum demand that is lower than the sum of every connected load, which lets you size the supply and main switch sensibly.

How is diversity applied to a cooker?

For a household cooker the On-Site Guide allows the first 10 amps of the rated current in full, plus 30% of the remainder above 10 amps, plus 5 amps if the cooker control unit includes a socket outlet.

Do EV chargers and immersion heaters get diversity?

Generally no. Thermostatically controlled water heating and electric vehicle charge points are usually taken at 100% of their rating unless load management or dynamic control is in place, because they can run at full load for long periods.

Maximum Demand Calculator with Diversity (UK Domestic)

How diversity is applied

Adding up every connected load gives a figure far higher than an installation ever draws, because the loads do not all peak together. The On-Site Guide gives allowances for each type of circuit in a single dwelling, and this tool applies them like this:

Lighting 66% · Sockets: largest + 40% of the rest · Cooker: 10 A + 30% above 10 A (+5 A socket)
Showers: largest + 25% of the rest · Water heating, heating, EV, other: 100%

Each load is converted to a current at 230 V, the allowance is applied, and the results are added to give the assessed maximum demand. That current then sets the supply, the main switch and the tails.

Where the figures come from

These are the single-household allowances from the IET On-Site Guide. Other premises, blocks of flats and three-phase supplies use different tables, and modern loads such as EV charging and heat pumps are often taken at full load unless a load-management scheme is in place.

Common questions

Is this for a single house?

Yes. The allowances used here are the single-dwelling figures. Flats, commercial premises and three-phase supplies follow different diversity tables.

Why is there no diversity on the EV charger?

A charge point can draw its full rating for hours, so it is normally taken at 100%. Where a load-management or dynamic-control system limits it, a lower figure can be justified.

Does it size the cable and main switch?

It gives the assessed demand in amps and suggests the next standard main-switch rating. The final cable and device selection still needs the full design checks.

Maximum Demand Calculator

How diversity is applied

Where the figures come from

Common questions

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