What are electrical safety zones and where are they?
Where are electrical wiring safety zones?
Before you drill into a wall, it helps to know where electrical cables are likely to run. This illustrated guide explains the prescribed cable zones used in UK installations — and why a 'safe zone' is not a safe place to drill.
Technical guidance reviewed: 26 October 2026Putting up shelves, hanging pictures or fitting a television bracket? Concealed cables can be damaged by screws and drill bits. UK wiring rules define prescribed zones where certain concealed cables may be routed. These are predictable routes, not confirmation that a wall is free from cables elsewhere.
The three main prescribed zones
1. Above or beside an accessory
A cable may run directly vertically or horizontally to a visible socket, switch or other electrical point. Its zone extends across the relevant width or height of that point.
2. Near the ceiling and corners
A zone runs within 150 mm from the top of a wall, and within 150 mm of an angle between adjoining walls or partitions.
Do cables always go straight up or down?
No. A cable may run horizontally or vertically to an accessory or be routed within the 150 mm perimeter zones. It is not correct to assume every cable goes straight up from a socket, or that a space between sockets is cable-free.
What about the opposite side of a wall?
For walls or partitions 100 mm thick or less, the location of a point or accessory on the other side may establish a prescribed zone on this side too. A seemingly blank wall can therefore contain wiring serving a room next door.
Do concealed cables need RCD protection?
For many ordinary low-voltage cables concealed less than 50 mm below a wall surface, BS 7671 requires additional protection by a 30 mA RCD, unless an applicable protective wiring method or other permitted exception is used. In walls or partitions containing internal metallic parts, specific requirements apply irrespective of depth. Consult Regulations 522.6.202 and 522.6.203 and the applicable provisions of 522.6.204.
Recognised alternatives can include suitably earthed metallic cable coverings, earthed conduit/trunking or mechanical protection adequate against penetration — subject to all relevant requirements. Plastic capping alone is not reliable mechanical protection against a drill or screw.
Before drilling
- Check both sides of the wall for sockets, switches and fixed electrical equipment.
- Identify likely cable routes and look for signs of alteration.
- Use a suitable cable and pipe detector in accordance with its instructions; understand that detectors can miss cables.
- If the route is uncertain, arrange an inspection or select a different fixing position.
When not to proceed
- The detector indicates a cable or metalwork.
- The wall is thin, contains metal framing or has wiring on the reverse face.
- Previous work suggests unusual cable routing.
- There is any doubt about the route or depth of the cable.
Common questions
Is it safe to drill 150 mm below a ceiling?
No location is automatically safe. The prescribed top-of-wall zone is itself a place where cables may be installed, and cables can be elsewhere too.
Can cables run diagonally through walls?
Conventional concealed low-voltage wiring without an alternative permitted protective method should follow prescribed zones. Alternative protective methods and legacy or non-compliant work mean you must not rely on this as proof that no diagonal cable exists.
Is a cable detector enough?
No. It is a useful aid, not proof of absence. Detection is affected by depth, wall construction, metallic objects and whether cables are energised.
Does RCD protection make it safe to drill into a cable?
No. An RCD is an electrical protective measure, not permission to damage a cable. Mechanical damage can cause shock, arcing, burns, fire or loss of supply.
Is plastic capping adequate protection?
Ordinary plastic capping can assist with cable positioning and plastering but is not equivalent to protection able to withstand a nail or screw.
Are the rules different in a kitchen or bathroom?
The concealed cable rules remain relevant, but special locations such as bathrooms have additional requirements under Section 701. Other electrical equipment and services may also affect the choice of fixing location.
Further reading and electrical services
Technical references
Basis: BS 7671 Section 522.6, particularly Regulations 522.6.202–522.6.204 (check the edition and amendment applicable to the installation). This is a practical overview, not a substitute for the complete regulation wording or a site assessment.
Electrical Safety First — Wiring Regulations help · IET Wiring Matters — Concealed cables and RCD protection
Article checked: 26 October 2026. Older guidance documents are linked for background; refer to the current BS 7671 text for a specific installation.
Unsure what is behind your wall?
NOD Electrical Services provides electrical fault finding, rewiring and inspection services throughout Streatham and South London. If a concealed cable route is uncertain, we can assess it before you make an expensive mistake.
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