What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Same thingchase
also chasing, safe zone, prescribed zone, wall chaser
SAFE ZONE is the term that matters — the bands of a wall where a buried cable may run, so that anyone drilling later knows which strips to avoid.
Australia
Close, not identicalchase
also chasing, notching, conduit chase
Chasing masonry is limited in the same way, with the practical difference that domestic cable is more often run in conduit within framed or furred walls than buried in solid masonry.
United Statesyours
Same word, different thingchase
also notch, bore, pipe chase, raceway
A CHASE is more often a vertical shaft carrying services between floors than a groove in a wall. Cutting a stud is a NOTCH or a BORE, and those have their own separate depth limits.
Canada
Same word, different thingchase
also notch, bore, service chase
As the United States, with notching and boring limits set as fractions of the member's depth and protective plates required where a fastener could reach the cable.
The governing standard, by market
United Kingdom
BS 7671 Section 522 / Approved Document A
Protection of cables concealed in walls including the permitted zones, and limits on chasing to masonry walls.
United States
NEC 300.4 / IRC R602.6
Protection of cables against physical damage including nail plates, and limits on drilling and notching of studs and plates.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- What is a safe zone and why does it exist?
- It is a band of wall where a buried cable is permitted to run, and it exists so that someone drilling into a wall years later can predict where not to drill. British wiring rules define the zones geometrically: a horizontal band within a set distance of the top of the wall, vertical bands running up and down from an accessory such as a socket or switch, and bands along the corners where two walls meet. A cable outside those zones has to be protected — armoured, in earthed conduit, at sufficient depth, or on a circuit with residual current protection. The zones are not a guarantee, which is why a detector is still the right first move, but they are the reason a cable runs straight up from a socket rather than diagonally to save a metre of cable.
- How deep can a chase be cut into a wall?
- Shallow enough that the wall is still a wall, and the limits are expressed as fractions of its thickness. British guidance allows a vertical chase to about a sixth of the leaf's thickness and a horizontal chase to about a twelfth, and horizontal is more restrictive because it cuts across the direction the load travels — it reduces the section resisting a vertical load along the whole length of the cut, where a vertical chase weakens a narrower strip. Chases must not be cut back to back on opposite faces of the same leaf, must not be cut in a hollow block whose shell is thinner than the chase, and must never be cut into a cavity wall's leaf so deeply that the cavity is broken into. Cutting a chase across a lintel or a padstone is the case that causes real structural damage, because the material removed was doing concentrated work.
- Why do American walls need nail plates when British walls need zones?
- Because the hazard has a different shape in each construction. In a framed wall the cable runs through a bored hole in a stud, so the danger is a fastener driven into that stud face at the height of the hole — the answer is a steel plate over the stud edge, protecting a specific known point. In a solid masonry wall the cable is buried in plaster over a chase and could be anywhere, so the answer is a rule about WHERE it may be, enforced by convention so that drilling elsewhere is reasonably safe. Neither approach transfers: a nail plate is meaningless in masonry because there is no member edge to protect, and a safe zone is weaker in a framed wall because a cable can be pulled through anywhere between the studs. A house using both constructions needs both disciplines, applied to the right walls.