Approved Documents A, B, C, E, F, L, MHow deep can you chase a wall?

Worth doing: writing your own summary of every Approved Document. It's good exam prep.

A: Structure (notches, holes and chases)

Electrician's Guide to the Building Regs · 10.1.1 Notches and holes in joists (table and figure) · p.166 Electrician's Guide to the Building Regs · 10.1.2 Chases in walls · p.167 On-Site Guide · 7.3.1 cables through joists at least 50 mm from the top or bottom (or protected, 522.6.204) · p.102 On-Site Guide · Figure 7.3.1 Cables through joists · p.103 On-Site Guide · 7.3.2 and Table 7.3.2 cables in walls · p.104

B: Fire safety

Fire barriers where cables pass through walls and floors, and smoke and heat alarm positions (including loft conversions). Smoke and heat alarm questions do come up in the Building Regs exam.

Electrician's Guide to the Building Regs · Part B, fire safety and smoke/heat alarms · from p.168

C · E · F · L

• C: site preparation and resistance to contaminants and moisture. Stop gas and water getting in where cables enter.
• E: resistance to the passage of sound. Cables running through sound insulation have a reduced current-carrying capacity. Take care with recessed downlights in ceilings that contain sound insulation.
• F: ventilation.
• L1: conservation of fuel and power in dwellings. Energy-efficient lighting and automatic control of outside lights.

M: Access to and use of buildings

• When rewiring or altering an existing circuit, you don't have to meet Part M. The finished installation just has to be no less accessible than it was before.
• When refurbishing or rewiring, it's fine to mount switches and sockets in keeping with the existing property.

Electrician's Guide to the Building Regs · Approved Document M: switch and socket heights figure · p.186 Highlight or tab this image

P: Permitted cable routes

Cables hidden in walls must run in the permitted zones: horizontally or vertically in line with an accessory, or near the wall's edges and corners. If a cable runs outside the zones, e.g. diagonally between two outlets, and is less than 50 mm deep, it needs an earthed metal covering, earthed conduit or trunking, or mechanical protection against nails and screws. RCD protection is not a substitute for the zones. Capping over cables in a chase is common, but it's extra mechanical protection rather than a requirement.

Electrician's Guide to the Building Regs · Permitted cable routes / zones figure (blue = OK, orange = needs extra protection) · p.43 On-Site Guide · Similar permitted-zones figure