Electrical back box

Abstract

An electrical back box 10 suitable for inserting into a hole in a plasterboard wall. The back box 10 comprises a base 12, with at least one wall 11 extending therefrom, suitable for housing electrical

Description

FIELD OF THE INVENTION The invention relates to electrical boxes designed to be fixed into a wall or ceiling, and more specifically, but not exclusively, dry lining boxes intended for use with plasterboard walls. BACKGROUND When building a house, apartment block, office block, or other building, it is common to use plasterboard (also known as drywall) to create the interior walls. The plasterboard may be installed on to a brick wall, or mounted to a wooden or metal frame to create interior rooms in the building. These buildings require electrical switches and sockets to be installed in the plasterboard wall, and so need a back box (hereinafter called a box) fixed to the wall to contain the electrical cables. A face plate can then be fastened to the front surface of the box and provide a user interface. Boxes are currently fixed to the plasterboard wall using features of the box itself. The front surface of the box comprises a flange to limit the depth to which the box can travel into the plasterboard. To prevent the box falling out of the wall, known boxes also comprise two flaps, known as lugs or wings, which sit behind the plasterboard when the box is installed. The flaps are mounted to the box in such a way that they can be folded inwards to aid installation and are slidable in the depth dimension of the box. The flaps generally comprise a threaded hole so that, once the face plate is tightened into place using screws which engage with the threaded hole, the flaps are pulled against the rear side of the plasterboard, the plasterboard thereby being clamped securely between the flaps and the flange. Some buildings, such as commercial buildings, must comply with fire regulations. This means that a thicker, more fire-resistant plasterboard (sometimes known as fireboard) must be used for the building to comply. Known boxes may not be suitable for these thicker boards because the flap can only slide a set distance in the depth direction to accommodate the board. As a result, deeper boxes are available which help to overcome this problem, however these require more space behind the plasterboard than is often available. This problem, in practice, generally leads to installers using the shallower boxes, and either (i) modifying the box, or more commonly (ii) modifying the plasterboard by cutting a notch to accommodate the flap. These modifications may lead to safety concerns in the fire rating of the plasterboard, and also installers using power tools for extended periods of time. Further, the modifications take time to make, and even a small amount of time is important when fitting large numbers of boxes in a building. The same issue also presents itself when the hole for the box is close to part of the wooden or metal frame that supports the plasterboard. Again, there must be some form of modification to make the box fit into the wall. SUMMARY OF THE INVENTION A solution is therefore required which is more time efficient to fit, and which requires no manual manipulation of the box or plasterboard, regardless of its thickness. To solve the problems identified above, there is provided an electrical back box as set forth in claim 1 of the appended claims. Preferred features of the invention are set forth in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of an electrical back box, Figure 2 is a front view of the box, Figure 3 is a partial view of the box showing a translatable screw hole, Figure 4a is a partial view showing an alternative translatable screw hole, and Figure 4b is a partial view showing the alternative translatable screw hole from a rear view. DETAILED DESCRIPTION OF THE INVENTION Figures 1 and 2 illustrate a box 10 intended to be installed by being pushed into a hole created in a plasterboard wall (not shown). The box 10 comprises four walls 11, a base 12, and a flange 14. After being installed, a face plate (not shown) is fitted to cover the box 10 and provide a user interactable feature, such as a switch, socket, or button. The four walls 11 of the box 10 preferably taper from the flange end 14 to the base end 12, i.e., the distance between the top and bottom walls 11, and / or the two side walls 11 may be reduced at the base 12 compared to the flange 14. The tapering of the walls 11 increases friction between the walls 11 of the box 10 and the cut-out in the plasterboard. Such increased friction makes the box 10 fit more securely the further it is pushed in, and thus reduces the likelihood of it falling out of the plasterboard wall. To prevent the box falling behind the plasterboard, potentially into a cavity where it would be irretrievable, there is provided the flange 14 to abut the plasterboard wall and limit the penetration of the box into said wall. The flange 14 is illustrated as extending the whole way around the opening created by the four walls 11. Although this is preferable, less of the perimeter comprising a flange 14 would also be acceptable as it would still serve its purpose of limiting penetration. On an exterior of the walls 11 of the box 10, i.e., the surface configured to engage the plasterboard, there are provided a plurality of projections 16. The projections 16 increase (or further increase, in embodiments comprising tapered walls 11) the mechanical grip the box 10 has on the plasterboard. Although the invention is functional with projections 16 featuring on only one wall 11, there are preferably projections 16 on two opposing walls 11, and more preferably on all four. Any number of projections 16 may be used, and the exact number will depend on many factors such as the size of the box (an aerial socket box being much smaller than a double socket box, for example), and the width of each projection. For example, a single projection 16 may span substantially the whole width of the wall 11, the width defined as the dimension parallel with the flange 14. Alternatively, several projections 16 may be used, spaced across the width, as shown in Figure 1. The projections 16 may be the same height along their length, or may be taller at the flange 14 end of the box than the base 12 end. The projections 16 preferably extend substantially the whole depth of the box 10, the depth defined as the dimension extending from the flange 14 to the base 12. A projection 16 extending the substantially the whole depth of the box 10 is usable on a greater number of plasterboard thicknesses, and also increases security by increasing the mechanical engagement with the plasterboard. Each projection 16 may be in the form of a plain blade, or may be barbed to help prevent the box 10 falling out of the plasterboard wall. The projections 16 are more preferably in the form of saw-toothed projections 16 as shown clearly in Figure 1. The saw-toothed projection 16 may be orientated such that the side of the tooth substantially perpendicular to the walls 11 face the flange 14 end of the box 10. To increase engagement with the plasterboard, the saw-toothed projection 16 may increase in width towards the flange end 14. In use, the box 10 is simply pushed into a hole in the wall, the hole preferably being dimensioned approximately the same size as the base 12. As the box 10 is pushed into the wall, its walls 11 deform slightly. However, the box 10 is resilient and the spring force of the material produces a force opposite that imparted by the wall, the box 10 attempting to adopt its natural shape and size. This spring force, coupled with the projections 16, increases mechanical grip of the box 10 by forcing the projections 16 into the bore of the hole in the wall as well as anchoring it from behind the wall. The base of the box 10 preferably includes a knockout section (not shown) that can be pushed to create a hole so as to allow electrical cables to be passed through. Knockout sections may also be provided on the walls 11 of the box 10. In some embodiments, the knockout sections may be concentric circles to allow a user to choose the diameter of the hole they wish to create. A larger diameter hole may be required, for example, if the cables are of a greater thickness, or if a higher number of cables are to be passed through the hole. After fitment of the box 10, the cables are wired into a face plate to establish an electrical connection between, for example, a switch and a light bulb. Face plates may connect to the box 10 using screws. The screws pass through the face plate and engage with threaded holes 18a, 18b on or connected to the box 10. The threaded hole 18a may be provided by using a threaded insert, which may be push-fitted into the box 10. The position of the threaded hole 18a is fixed relative to the box 10. It will be appreciated that threaded inserts are not essential but are preferred to simplify manufacturing and to create a longer lasting product compared with forming the threads in the box 10. The threaded hole 18b may be vertically moveable in order to allow the face plate to be mounted level even if the box 10 has been installed at a slight angle, which is frequently the case in practice. A moveable threaded hole 18b can be implemented using the system shown in Figure 3. The interior wall 11 of the box 10 has clips 20 dimensioned to accept arms 22 of a moving nut 24. The clips 20 are spring biased into a position which does not allow the moving nut 24 to fall out and are round ended to ensure security. The moving nut 24 is constrained and can only move in the vertical direction. As the moving nut 24 comprises the threaded hole 18b, the threaded hole 18b is also moveable vertically and allows for face plate adjustment. Another system for allowing the threaded hole 18b to move vertically is illustrated in Figures 4a and 4b. This alternative system comprises a body 26 having arms 28. The arms 28 serve to prevent the body 26 from passing through the hole 30 in the wall 11. The outer side of the wall 11 comprises a slot 32 in which curved legs 34 of the system engage and allow a sliding motion. It will be appreciated that for maximum adjustability, both threaded holes may be moveable. Conversely, to enable a cheaper manufacturing cost both threaded holes may be fixed. All components of the box can be made from any material which offers some resilience, complies with local regulations and is known in the art. Such materials include Polyvinyl Chloride (PVC), Acrylonitrile Butadiene Styrene (ABS), urea formaldehyde, or a polycarbonate. It will be appreciated that some deviations from the above-described structure fall within the scope of the claims. For example, although four walls are typical in the industry, the invention encompasses embodiments having any number of walls. In one embodiment, 5 the box has only one wall, which may be circular in cross section. Further, in the above embodiment, the projections 16 are described as preferably extending substantially the whole depth of the box. It will be appreciated that the invention lies in the inclusion of the projections 16, and not their exact size. It is within the scope of the present invention to provide projections that extend, for example, 50%, 60%, 70%, 80% or more of the i o depth of the box 10. 02 04 24

Claims

1. An electrical back box for inserting into a hole in a plasterboard wall, the back box comprising:a base, with at least one wall extending therefrom, for housing electrical cables, wherein the at least one wall defines an opening opposite the base; anda flange extending at least partially around the opening for abutting the plasterboard wall and limiting penetration of said plasterboard wall, wherein the at least one wall is resilient and configured to elastically deform upon insertion into the hole, and at least one of the resilient walls comprises at least one projection for gripping a bore of the hole in the plasterboard wall.

2. The back box of claim 1, wherein at least one projection features on each of two opposing walls.

3. The back box of claim 1 or 2, wherein the projections extend along the walls between the flange and the base.

4. The back box of any preceding claim, wherein each projection is barbed.

5. The back box of any preceding claim, wherein each projection comprises a line of saw-tooth shaped teeth, the shorter edge of the sawtooth orientated towards the flange.

6. The back box of claim 5, wherein the teeth at a base end of the back box are smaller than those at the flange end.

7. The back box of claim 5 or 6, wherein the teeth at the base end of the back box are narrower than those at the flange end.

8. The back box of any preceding claim, wherein the walls taper from the flange end to the base end in order to provide additional frictional engagement between the back box and the plasterboard.

9. The back box of any preceding claim, wherein the back box comprises two threaded holes.

10. The back box of claim 9, wherein at least one of the threaded holes is vertically moveable, thereby allowing adjustment to the angle of a face plate.

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