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Maximum Demand & Diversity Calculator

BS 7671:2018+A4:2026

After-diversity board demand current — Tables 3.1 and 3.2, IET Electrical Installation Design Guide Ch.3.

Installation Setup

Table 3.2 — Simple diversityTable 3.3/3.4 in Section 03

Applying Table 3.2 diversity — Household / Individual Dwelling (Column 1)

Load Builder

#1
Ib per unit: 32.00 A  ·  Row total (×1): 32.00 A
1 load rowPi_board (installed): 32.00 A

Level 2 Cascade to Main Intake

Diversity Method at Intake Level

Distribution Boards — Ib_board inputs

Pi_board — Installed load

32.00

A

No diversity applied

Diversity method

Table 3.2 · Col 1

Household / Individual Dwelling

Ib_board — Board demand

32.00

A — after diversity

Eq 50
32.00 A→32.00 A

Diversity Groups (1 group)

Row 9 · 1 load32.00 A → 32.00 A
13A socket-outlet circuit×132.00 A

Step 1 — Job 1: Design Current per Load (Table 3.1)

13A socket-outlet circuitIrated32.00 A/unit × 1 = 32.00 A

Step 2 — Job 2: Diversity per Group (Table 3.2)

Row 9 — Design Guide 100% largest + 40% others
32.00 A → 32.00 A

Step 3 — Board Demand (Eq 50)

Pi_board32.00 A (installed, no diversity)
Ib_board= 32.00 = 32.00 A

BS 7671:2018+A4:2026 | IET Electrical Installation Design Guide Ch.3

Table 3.1 (demand rules) | Table 3.2 (diversity allowances) | Equations 46–50

Questions

›Does BS 7671 allow diversity in maximum demand?

Yes. Regulation 311.1 requires the maximum demand of an installation to be determined, and allows diversity to be taken into account in doing so. BS 7671 does not give the allowances itself. This calculator uses Tables 3.1 and 3.2 of the IET Electrical Installation Design Guide.

›Which premises types does the calculator cover?

The three columns of the diversity table: household or individual dwelling, small shop, office or business, and small hotel or boarding house. The premises type you choose sets which column every load group is diversified against.

›Which loads get no diversity?

Thermostatically controlled water heaters, floor warming installations and thermal storage space heating are taken at 100% of their load. The calculator places each of these in its own group, so they are never reduced.

›How are standard household socket-outlet circuits diversified?

In a household, 100% of the largest socket-outlet circuit is taken, plus 40% of every other socket-outlet circuit. The diversity groups panel shows each group before and after its allowance, so you can see where the reduction comes from.