Flush-mounting boxes and cover frames: European sizing and depth

60 mm fixing centres: the dimension everything depends on

Almost all flush-mounted wiring accessories on the European continent are fixed into a round box with an internal diameter of around 60 mm and two screw holes set 60 mm apart, centre to centre. That fixing distance is laid down in the German standard DIN 49073 and is the de facto standard in the Netherlands, Belgium and Germany. The mechanism (switch, socket outlet, dimmer or data outlet) sits on a metal mounting ring that is secured in the box with two screws. Most mounting rings also have expanding claws that bite into the box wall as they are tightened.

For you as an installer this means the inserts of Liregus Alfa and Liregus Modern fit any standard flush box with 60 mm fixing centres, whatever the brand of box. On a refurbishment you therefore do not need to replace the boxes, as long as they are undamaged and sit flush. Where the wall cannot be opened, Lichtplein supplies matching surface-mounting boxes in both series.

Depth: 47 mm as standard, 63 mm for dimmers and data

The standard depth of a dry-lining box is around 47 mm with most manufacturers. That is enough for a single-pole switch or a socket outlet with one cable coming in. As soon as more has to go into the box, choose the deep version of around 63 mm (61 to 65 mm depending on the manufacturer). That is essential for:

• rotary dimmers and electronic switches, whose electronics behind the mechanism need an extra 10 to 15 mm
• socket outlets with a USB charger, because the power supply for the USB ports sits in the insert
• RJ45 and coaxial data outlets, whose cable has a minimum bend radius and must be able to turn away behind the insert
• looped-through socket outlets, where two 3 x 2.5 mm² cables and the connectors need space together
• boxes with conduit entries on two sides, where the conductors cross each other

A rule of thumb for work preparation: if in doubt, take the deep box, because a box that is too tight costs a great deal of time at second fix. In a tight box conductors get kinked, connectors press against the mechanism and the insert sits at an angle, so the cover frame no longer lies flat against the wall.

Hollow wall or masonry: different box, same dimensions

In plasterboard, gypsum fibreboard or a timber-framed lining you use a dry-lining box. Cut the hole with a 68 mm hole saw and fix the box with clamping lugs that tighten behind the board; many models suit board thicknesses of roughly 7 to 35 mm. Do not overtighten the clamping screws, or the lugs pull through the plasterboard.

In brick, sand-lime block and concrete you use a flush box for masonry. Set it in a cored or chased hole with plaster or mortar, with the front exactly level with the finished wall. Level the box with a spirit level before the plaster sets. A box plastered in crooked cannot be straightened afterwards: the screw holes then lie on a diagonal and the cover frame follows that angle.

For a wall in the airtight envelope of an energy-efficient building, choose airtight boxes with membrane entries for the conduit. An ordinary box is a leak in the airtight layer there, and that shows up in the blower door test.

Multi-gang cover frames: 71 mm centres

A 2-, 3-, 4- or 5-gang cover frame assumes that the mechanisms sit exactly 71 mm apart, centre to centre. That is the European standard dimension for combination frames and applies both horizontally and vertically. So use linkable boxes that clip together at 71 mm, or a pre-formed 2- or 3-gang box. Placing loose boxes side by side by eye often goes wrong in practice.

The tolerances are small. With a 1 mm error per box, the last insert of a 4-gang frame is already 3 mm out of position and the inserts pull the frame out of true. With slim, flat cover frames such as those of Liregus Modern this shows sooner than with a thicker frame. So work with linking pieces or a drilling jig and check the 71 mm with callipers before fixing the boxes.

Also watch the orientation: all inserts in one frame must face the same way, otherwise the frame will not drop over the mounting rings. Do keep frame, inserts and centre plates within one series and one colour, so that finish and dimensions match.

Common mistakes on site

• Box plastered in too deep: the frame stands off the wall and the claws do not grip. Keep the front level with the finished wall, at most 1 to 2 mm behind it.
• Box chosen too shallow: the dimmer or USB socket does not fit, conductors get kinked and the insert sits at an angle.
• Box set crooked: the frame follows the screw holes. Use the spirit level when plastering in, not only at second fix.
• Multi-gang boxes not at 71 mm: the frame binds, bows or does not fit.
• Claws in a dry-lining box: the thin box wall can crack. Fix the insert with the screws and use the claws only if the box manufacturer allows it.
• Too little cable length: leave at least 10 to 15 cm of conductor out of the box so the insert can be connected without pulling.
• Open conduit entries: plaster and dust run into the box and the entry breaks off. Close unused entries.

Mounting heights and a checklist for work preparation

In Dutch practice it is usual to set switches at 105 cm and socket outlets at 30 cm above the finished floor; above a kitchen worktop the height is usually between 110 and 125 cm. These are customary values, not a regulation: the project specification always takes precedence. Record the agreed heights on the installation drawing so that the openings are in the right place before plastering.

• Decide per position: hollow wall or masonry, standard or deep, single or multi-gang.
• Multi-gang: linkable boxes or a pre-formed combination box at 71 mm.
• Airtight envelope: airtight boxes and entries.
• Order inserts, centre plates and cover frames from the same series and colour: Liregus Alfa in white and sand, Liregus Modern in matt white, matt black, matt sand and champagne.
• Count cover frames per combination, not per mechanism: one 3-gang frame replaces three single frames.

Frequently asked questions