Height of Floor Outlets: Set-Out, Build-Up and Installation Tolerances

The first measurement of the height takes place on a blueprint whereas the second establishes the height on-site after it turns out the thickness of the constructions is 20 mm thicker than indicated in the drawing because it is the second option that matters the most.

As for the practical aspect of the issue, it raises the questions about the reference point, thickness of the floor, flushness of the electrical box, and distance of the socket from the ground.

In conclusion, it is very important to remember that the outlet should be measured from the finished floor instead of the structural slab. In general, the wall outlets are situated between the measurements of 300-450 mm in the middle of the outlet. The floor boxes could be either flush with the floor finish or no more than approximately three millimeters higher than the floor finish. It should be noted that pop-up units need to have around 60-90 mm above the surface before plugging them in. The height where the box finishes will be in the right position in the drawing depends entirely on the floor finishing material used.

The Floor Build-Up Is the Real Variable

The distance between the structural slab and the floor is occupied by three different thicknesses, all of which have to be determined after the trades come in.

• Screed (or self-levelling compound): It usually ranges from 40 to 75 mm and is hardly ever exactly that thickness as shown on the drawings.
• Adhesive (or bedding): Ranges between 5 to 15 mm for tiles, while for engineered timber the thickness is from 3 to 5 mm.
• Finish: It is usually between 10 to 20 mm for stone, from 8 to 15 mm for tiles, and from 15 to 20 mm for solid timber flooring.

So, in summation, the floor that was supposed to be at 60 mm is now made 85 mm in height. As a consequence, all the sockets are lowered by 25 mm in total in relation that they should have been located, and floor boxes built at the level of the slab will end up being located even lower than the floor level, which is exactly the gap that collects water and makes people trip over.

What makes it so that mistakes of this kind are avoided is a painstakingly boring procedure of marking the finished floor level on the walls with a permanent marker and using its level to set everything else after importing it into the room. The reference point should always be taken from the highest existing point, as otherwise a perfectly flat-looking floor will result in a mismatch between levels of sockets.

The Four Heights, Stated Plainly

The residential and commercial figures are convention instead of law in most jurisdictions, which is why they differ between countries and why the standards survey sits better in a dedicated reference: the market-by-market numbers, the spacing rules and the accessibility envelope are set out in this guide to the standard height of floor outlets.

What is important to note here is that the information remains constant throughout all regions. A 300 mm socket located in Germany, even though it has a height of 300 mm from ground level, will be considered wrong when judged from the slab level.

In-Floor Boxes: Flushness, Depth and Fire

Four factors are considered while assessing a floor box.

• Flushness. A flush box is expected to be between 0-3 mm above grade. Any flushness below is regarded as unacceptable as the recessed area fills with water, cleaning agents and other debris hence becoming unusable over time. In addition, if the box is above 3 mm, it becomes more than just a trip hazard.
• Set-out. For the box to set out on a tiled floor it has to be situated exactly on a tile modular, without straddling a grout line or ending up in a cut tile. This means that the box location is determined immediately after creating the tile layout. Also, within a cast slab, this involves creating the floor design ahead of the pouring.
• Content depth. A shallow stature restricts how the cables can bend and how many items can fit in the box hence its depth is very important. On the other hand, a box that contains two power sockets and a couple of data outlets, requires a lot more depth than a box with a power outlet.The selection logic is in this guide to choosing electrical boxes for outlets and switches.
• Fire and water rating. If a box goes through the rated floor, it needs to be covered to meet the standards for any given assembly hence thereby rendering the box useless. Also, if the floor is washed out or gets wet, the gasket becomes a consumable item which shouldn’t be disturbed while making a new room.

Two site plans alter everything. When working on a post-tension floor slab, the installation of a new box becomes a problem without the involvement of an engineer. However, with a raised-access floor, there is no problem with slab thickness, but instead, the only limitation becomes the panel module and the weight limit of the tile.

Pop-Ups: The Plug Is Taller Than the Unit

A pop-up measuring 90 mm might sound very useful until a plug is put on the device. The height of the British Standard 13 A plug is approximately 50 mm tall, the EU Schuko is about 55 mm tall, while the built-in plug of a laptop adapter is likely to measure around 60 mm. This gives us an obstruction of at least 140 mm, not 90 mm.The following numbers determine the operability of a pop-up:

• Cavity depth: it can be between 100 mm and 200 mm, which means that thin screed and countertop having a drawer directly below can be ruled out.
• Lid travel clearance: area behind the unit, chairs, and cabinet doors must be taken into account.
• Plug envelope: height of the unit plus height of a plug indicates if the device fits the required space.
• Cable exit: either side exit or top exit, as both require appropriate space for their operation; side exit is more space-consuming, top exit is less space-consuming.

The same logic works with a countertop as well. It must not obstruct the backsplash nor the zone of activity, and in addition to that, wiring must not intersect with the hot plate.

Where the Socket Goes Relative to What Sits in Front of It

Height is just part of functionality. What’s in front of the appliance makes up the other half.

A socket at a height of 300 mm behind a 900 mm deep worktop complies with official standards and is unreachable. A socket at a height of 450 mm behind a desk 600 mm deep can be reached by someone sitting at the desk only. A floor box placed under the conference table is useless if there’s a solid board along the base of the table without any space left.

The golden rule is to start from the furniture and not the wall. Draw the layout of your furniture and measure the area along the wall. After that, find the spot for the electrical boxes and test if the plug does not touch the drawer, skirting or radiator. The wiring sequence that follows — box fill, conductor capacity, termination — is described in this guide to installing a power outlet.

Commercial Floors: Boxes on a Grid

In workplaces and public area, floor boxes are assembled in a grid that relies on furniture structure, as opposed to the wall framework. The distance between the boxes generally varies between four and six metres and is determined based on modular workstations allowed by the office layout, which guarantees that the distance from any desk to the box is no more than standard lead length.

This leads to three basic requirements.

• Furniture arrangement must be determined before building floor boxes. Otherwise, the arrangement of the grid of boxes will fall under an incorrect desk arrangement.
• It is important to follow the structural grid where possible because a floor box set in between the beams is simpler to assemble than the one placed in front of beams.
• We should consider future changes. Although a box can move data and electricity in ten years, it can be changed twice without great cost since buying a slightly larger box with extra modules costs less than making a secondpour.

It is worth mentioning that any floor box can represent the frames with standard wall plates in it.A media plate such as this wall-mounted HDMI socket is the kind of module that ends up in one, which is why the depth of the box and the depth of the plate have to be considered together.

Retrofit and Renovation

Inserting a floor box into an already set slab entails core drilling along with three additional requirements needed to complete the process.

The core is required to stay clear of reinforcements and post-tensioning cables, which implies using a scanner and hiring an engineer for post-tensioned slabs. In addition to this, the drilling process is required to be conducted efficiently so that fire and water-proofing are ensured, rather than just filling the hole with mortar. It also means that the drilled hole has to stay deep enough to fit in a proper service; however, shallow slabs require shallow holes and therefore reduce the number of devices that can be used.

When it comes to low wall socket installation into the solid wall, similar principles apply: the back box depth keeps the modules of 45 mm deep from fitting and it gives no trouble if it is reasonably easy to drill the brick wall for a 47 mm back box.

What Goes Wrong on Site

• The box is raised from the slab. This issue may not be obvious until the floor is laid.
• The box is raised above the tiles. With a 5mm lip, a broken edge tile means there is a possible trip hazard.
• There is a grout line on the plate. A row of sockets across the joint does not look right, and it is up to the tiler to decide whether this is acceptable.
• There is a pop-up without a cavity. This can only be found during the second fix, with no options other than a shallow unit or cutting into the cabinetry.
• There is a single height for a mixed-use development. Different building uses have different conventions, and a one measurement fits all approach will not work for mixed-use buildings.Where a project mixes device types, matching the plate family to the local convention is the cheapest way to keep it consistent, which is what our wall switch and power outlet manufacturing is arranged around.

FAQ

What is the standard height for a floor outlet?

For the case of a wall box outlet, from 30 cm to 45 cm from the center to the top surface of the floor. In the case of a genuine floor box outlet, there is no height, since the lid needs to be flush with the floor surface without protrusion.

How high should a pop-up floor outlet rise?

Usually, the outlet must be raised by 6-9 cm, but the height must be also calculated while taking into consideration the plug height, since it can measure from 5 cm to 6 cm. So, the space must be planned accordingly.

Is there a code requirement for outlet height?

There exist no definite regulations about the height of an outlet in most areas. However, there exist certain spacing rules and some public accessibility law for public buildings and rooms.

Can a floor box be added to an existing concrete floor?

Yes, core drilling is needed as long as the engineer has issued an approval regarding the post-tensioned slab.

References

• U.S. Department of Justice — 2010 ADA Standards for Accessible Design
• U.S. Access Board — Reach Ranges and Operable Parts
• International Code Council — Building and Electrical Provisions
• Flushmount — Floor Box Installation and Outlet Height Guidance
• UL Solutions — Floor Boxes and Wiring Device Certification

Conclusion

When measuring the box, keep in mind to consider the floor finish level, place the box after tiles are up, and verify the connector and the plate to avoid most of the problems concerning the installation of floor outlets.

In case your project requires a special module for the floor or for a countertop unit, please provide us with the plate, type of the module, and depth of the cavity, so we could inform you about the available options.