Small-power rules playbook, BS 7671 (draft)

Status: draft v0.1 for engineer review, not an approved NFE standard · Standard: BS 7671 (NFE's default) · Scope: apartment type A · Rule file: rules/bs7671/apartment_type_a_small_power.yaml · Owner: to be named · Last reviewed: 21 Oct 2026

This page holds the reasoning behind NFE's rules for where small-power sockets go on jobs under BS 7671. The YAML rule file holds the numbers that the electrical toolkit applies. BS 7671 sets no socket counts or positions, so these are NFE's own design rules, applied under it. They decide where sockets go; they don't replace the engineer's BS 7671 design checks.

The first draft was read off the engineer's own layout for the repeated apartment type on LSHA F6 (apartment type A: the two mirrored apartments, W and E) and was tried in the phase 1 pilot. So it records what we drew, not yet what we have agreed is right. Engineers: fill in the "To decide" items, correct anything that's wrong, and name who signs it off.

How to change a rule

1. Agree the change and write the reason on this page.
2. Change the YAML to match, and raise its version (v0.1-draft, then v0.2-draft and so on).
3. Add a line to the history table at the bottom.

A rule set is written for one standard, and the toolkit refuses to apply it to a job under another. When a job is governed by IEC 60364 or US EAS 811-1:2014, it gets its own playbook page and rule folder.

Defaults for every room

For reference, the research noted that England's Approved Document M puts switches and sockets in dwellings 450–1,200 mm above the floor (Electrical Drawing Tools Evaluation (Oct 2026)).

Rules by room: apartment type A (v0.1)

Overall, 27 of the 44 generated sockets landed within 1 m of the engineer's (median 0.58 m). Because the counts were read off the same drawing, matching counts prove nothing about design quality; the positions are the test.

Device types

The rules name device types. The toolkit's catalogue (src/nfe_electrical/data/catalogue.yaml), which the engineers also own, maps each type to an NFE symbol. A mounting height is set only where a pilot legend states one.

The catalogue also has a 20 A double-pole switch (dp_switch_20a) and a cooker control unit (cooker_control_unit), for when the kitchen rules cover them.

How a rule reads in the YAML

bedroom:
  - {type: socket_twin_usb, count: 2, place: pair, wall: bed_head, spacing: 2.4,
     why: "bedside pair either side of the bed head"}

• place: perimeter (spread along all usable wall), wall (spread along one wall), pair (two either side of a wall's midpoint), corners, beside_door, centre or at.
• wall: longest, shortest, long_sides (the two longest facing walls), bed_head (the wall the architect's bed is drawn against), media_wall (the wall a TV or media unit stands against), facing_<room type> (the wall backing onto that room, such as facing_pantry), opposite_door, or north, south, east or west. A list is tried in order.
• count: a number, or a count by area. For example, {per_m2: 8, min: 2, max: 6} means one per 8 m² of floor, at least 2 and at most 6.
• why: the reason, in one sentence. Keep it in step with this page.

Decisions needed

• Counts, walls and spacing for each room type above.
• A mounting height for every socket type (only the 1,200 mm high-level socket is on the drawings).
• Dining zones: sockets or not.
• Balconies: weatherproof sockets or plain twins, and on which wall.
• Kitchen islands: a floor-socket rule, and a symbol of its own instead of HIGHLEVEL.
• Rules for pantries, the far end of cinemas, bathroom shaver sockets and corridors.
• The door, corner and spacing clearances.
• Who owns this playbook, and who signs off each version.

History