Can I chase a cable into a wall myself?
The safe zone rules that govern where a cable may run, the depth and protection requirements, what chasing does to a wall structurally, and where an electrician has to be involved.
- Difficulty
- intermediate
- Time
- 1 hr
- Read
- 5 min
- Safety
- restricted
Short answer
Cutting the chase and making good is builder's work you can legitimately do, but where the cable may run is governed by safe zone rules and the electrical connection and testing is not owner work unless you are competent. Cables run vertically or horizontally from an accessory, or within 150mm of a corner or ceiling. Anything less than 50mm deep needs 30mA RCD protection or earthed mechanical protection.
The safe zones exist so that the next person to put a picture up can predict where the cables are. They are not a formality: a cable run diagonally across a wall is invisible to reasoning and often to detectors, and it will eventually be drilled. Understanding the zones is worth doing whether or not you ever cut a chase.
Safety
Step by step
- Learn the permitted zones.A cable may run vertically or horizontally directly from an accessory such as a socket or switch; within 150mm of the top of a wall; or within 150mm of an internal corner where two walls meet. Anything outside those zones must be at least 50mm deep, or have earthed mechanical protection, or be protected by a 30mA RCD.
- Understand the 50mm rule.A cable buried more than 50mm from either surface of a wall is deep enough that ordinary fixings will not reach it. Less than that, and it needs either metal capping that is earthed, cable with an earthed metallic covering, or 30mA RCD protection on the circuit — which is another practical reason modern consumer units matter.
- Scan the wall before cutting anything.A detector in both metal and live modes, along the whole route, at more than one sensitivity. Detectors miss things — plastic pipes, cables behind foil-backed board, cables in metal conduit — so also reason about where existing cables must run from the accessories you can see.
- Understand the structural limits.In a masonry wall, a vertical chase should not exceed a third of the wall thickness and a horizontal chase a sixth, and chases should not be cut back to back on opposite faces of the same wall. Over-chasing a single-skin partition genuinely weakens it.
- Never chase a diagonal.It is quicker, it looks tidy behind the plaster, and it is the single most dangerous thing you can do to a wall. Nobody drilling that wall in twenty years has any reason to expect a cable there.
- Cut the chase properly.Score both edges with a multi-tool or a wall chaser on the correct depth, then remove between them with a bolster and hammer or a chisel. A dust-extracted chaser saves an enormous amount of cleaning. Wear eye and respiratory protection — silica dust from masonry is a genuine health hazard.
- Protect the cable in the chase.Metal capping is common but only counts as mechanical protection if it is earthed. Plastic capping protects the cable from the plaster and from a plasterer's trowel, not from a drill. The protective arrangement is part of the electrical design, so agree it with whoever is doing the connection.
- Leave the electrical work to someone competent.Running the cable, terminating it and testing the result is the part that decides whether the installation is safe. Unless you can test what you have done, do the chasing and the making good and let an electrician do the rest — and get a Minor Works certificate.
- Photograph before you fill.A photograph of the open chase, with a tape measure in it, is the most useful thing you will ever leave for a future owner or for yourself. Store it with the house papers.
Tips
- Fill in two passes with bonding coat, letting the first go off, then skim. Filling a deep chase in one go is why chases crack along their line months later.
- If the wall is being replastered anyway, that is the moment to run every cable you might ever want. The chase is the cheap part.
- In a stud wall, drill through the centre of studs and use grommets or protective plates where the cable passes, and remember safe zone rules still apply to the finished surface.
Common mistakes
- Chasing diagonally between two points — It puts a cable where no rule and no reasoning predicts it. Every guide about finding cables before drilling assumes safe zones are respected; a diagonal breaks that assumption permanently.
- Relying on a detector alone — Detectors miss cables in metal conduit, cables behind foil-backed plasterboard and anything not carrying current at the time. They reduce risk; they do not eliminate it.
- Cutting chases back to back on a partition — Two chases opposite each other in a single-skin wall remove far more of its section than either does alone, and can compromise it structurally.
If it doesn't work
Detector reads inconsistently along the route
Cause: Metal in the wall, foil-backed board, or a cable in metal conduit — Fix: Do not proceed on an ambiguous reading. Reason from where accessories are, and open up cautiously by hand if you must.
Hit a cable while chasing
Cause: Cable outside a safe zone, or a missed detection — Fix: Stop. Isolate the circuit. Do not attempt a repair with tape or a connector buried in the wall — a damaged cable must be repaired in an accessible enclosure or replaced.
Chase cracks through the plaster months later
Cause: Filled in one pass, or filled with the wrong material — Fix: Rake it out, fill in layers with bonding, allow to dry and skim. Scrim tape over the chase helps on wide ones.
Wall is only a single skin of block
Cause: Limited depth available for chasing — Fix: Consider surface trunking, a dado run, or routing the cable in the void of an adjacent stud wall instead. Structural limits are not negotiable.
Questions people ask
Is chasing notifiable work?
Cutting a chase is builder's work and is not itself notifiable. What matters is the electrical work that goes in it — an addition or alteration to an existing circuit in an ordinary room is not notifiable in England and Wales, but a new circuit or anything in a bathroom or outdoors is.
Can I use surface trunking instead?
Yes, and it is a perfectly legitimate answer, especially in garages, workshops and where the wall is solid or listed. It is visible, and it is far easier to alter later.
What about a listed building or a conservation area?
Chasing historic fabric may need consent, and lath and plaster and historic brickwork behave very differently from modern block. Take advice before cutting anything in a listed building — unauthorised alteration is a criminal offence.