Safety Zones to Know About When Running Electrical Cable in Walls and Under Floor Boards

Summary: Where the safety zones for electrical cable are in your walls. This project explains why we have designated electrical safety zones for the walls in a given property and where they are so that you do not accidentally screw or hammer into a cable that has been concealed or chased into the wall. Whether you laying the cable, or just trying to avoid hitting own with your picture nail, knowing where the safety zones for hidden cables are, is pretty important.

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To reduce the risk that you could accidentally cut or screw into an electrical cable there are cable safe zones for electrical wiring on areas of your walls and these are the areas where concealed cables should be run.

Electrical cables should not be found outside these zones, although in many older (and some newer) properties they often are, so if you are chasing out areas of a wall or chopping sections out, this is someting to be aware of.

It is important to know where these safety zones are for two reasons; firstly if you are doing some of the first fix yourself, you must ensure that you keep to these zones, and if not you know what you need to do.

Secondly it is useful to know where these safety zones are if you are going to be drilling into a wall. By avoiding these zones you will reduce your chances of injury or accident greatly. You can focus your cable searching activities to a limited area.

So, where are these safety zones where all concealed cables should run?

Safety Zones for Electrical Cables in Walls

Thankfully they are fairly simple to understand. There are a number of electrical wiring safe zones in which the cables should run:

  1. Top of the wall – where the wall meets the ceiling there is a 150mm zone where cables should be run. It is at the top of the wall and runs horizontally around the whole wall
  2. The join between two walls – where one wall meets another, there is a safety zone on each wall for 150mm from the corner. This is the case if the angle where the walls meet is acute, as in the corner of a room, or obtuse as you would find on the edge of a chimney breast. These zones will always run vertically down the corner
  3. Horizontally from any switch or socket – The zone runs horizontally from both sides of the  socket or switch until it reaches a corner or an obstacle such as a door
  4. Vertically from any switch or socket – the safety zone runs the width of the socket or switch both up to the ceiling and down to the floor
Electrical safe zones for cables in walls

Electrical Cable Safety Zones when concealed inside walls

If a partition wall is less than 100mm thick, then the cable safe zone for a socket or switch will occur on both sides of the wall.

Safety zones for partition walls less than 100mm thick

Electrical Cable safety zones for partition walls less then 100mm can occur on both sides of the wall

Cables That are not in Electrical Cables Safety Zones

Sometimes it is not possible to run cables in these zones. It is allowed so long as the following guidelines are followed:

  1. The cable must be over 50mm below the surface. If the wall is made from metal then it will need RCD protection, or
  2. The cable should be armoured with an earthed armour or metal sheath, or
  3. The cable should be in metal trunking or conduit which is earthed or,
  4. It should have protection from at least 3mm steel

Running Cables Under Wooden Floors

Typically, it is much easier to run the cables under the floor, however this is not really possible when there is a concrete floor, hence the safety zones described above to run the cables down to the switches and sockets.

Where there are wooden floors you can run the cables under them, but there are some restrictions. The cable must be at least 50mm from both the edges of the joist, in effect 50mm from the ceiling below or the floor above.

Cables passing through under floorboards

Cables passing through under floor joists must follow electrical guidelines

There are rules about where you can notch and drill through joist too. This weakens the joist and therefore is controlled to ensure that the joists are safe. We have more information and a handy joist notch and hole calculator to make life easier – click here.

If these guidelines cannot be followed the cable needs to be protected as described above.

Other Electrical Zones

These safety zones for electrical cables should not be confused with the zones that are used in a bathroom to determine which electrical appliance can be used. You can find more about these on the IET website.

Using and sticking to the safety zones for electrical cables is in everyone's interest. It is worth knowing about them for anyone who is doing DIY particularly if it involved fixing anything to a wall that might unwittingly come into contact with an electrical cable.

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