The present invention relates to an electrical back box, particularly, but not exclusively, a circular electrical back box.

Domestic and commercial lighting and mains switches are typically mounted to an electrical back box arrangement which provides a relatively standardised junction for connecting wires of the circuit together and to electrical terminals of the switching or other arrangement. For many years, in most countries, standard practice has dictated that such electrical back boxes (and the associated switching or blanking plates which are mounted thereto) are to be of a rectilinear shape such as a rectangular or square shape. However, this requires a corresponding rectilinear aperture to be cut in, typically using a pad saw (in the case of a plasterboard mounting surface) or recess routed out (in the case of a solid mounting surface) in order to receive the back box therein. It is notoriously time consuming and laborious for a user to form such rectilinear apertures or recesses since most cutting tools are ill suited to doing so. Also, if the formed aperture or recess is incorrectly sized or shaped, it can be difficult and time consuming to repair. Furthermore, some older buildings have lath and plaster interior walls. Wooden slats are run horizontally and are fixed at the wall studs and then covered in plaster. A spacing of about 10 mm is provided between adjacent slats so that the plaster can seep into the spacing. The 'curls' of seeping plaster are called keys and are necessary to keep the plaster on the lath. It is well known that creating apertures in such walls is problematic. Creating the aperture removes the support fixing at one end of the relevant slats, and the sawing action using a pad saw disturbs the slats and destroys the integrity of the lath/plaster matrix. At present it is necessary for a joiner to repair the wall in the vicinity of the formed aperture. And the back box must be mounted to the wall frame. Many back boxes for plasterboard include a pair of lugs for maintaining the back box in position within the aperture. Each lug includes a threaded aperture for receiving a screw of the switch plate. As the user screws the switch plate to the back box, this draws the lugs towards the user and into gripping contact with the rear of the plasterboard. Typically, the dimensions of each lug are about 25 mm in length and 10 mm in width, giving a maximum contact surface area of about 250 mm ² for each lug or 500 mm ² in total. The 'width' is defined in the direction extending away from the body of the back box. A circular back box is described in UK Patent Publication No. GB2450881. This allows a user to bore a circular aperture or recess and then mount the circular back box therein. However, these have not been widely adopted for a number of reasons. One reason is that the circular back box does not allow the universal fitting of any square switch plate. For example, three way switches include more components at their rear surface and these components extend too far in the plane of the wall to fit into the circular aperture and circular back box.

According to a first aspect of the present invention there is provided an electrical back box for mounting in a hole of a mounting surface which defines a plane, the back box comprising:

a body having a side wall of substantially circular outer profile; and

a flange member adapted to contact the mounting surface when the back box is inserted into the hole, thereby preventing further insertion,

wherein the back box includes existing or formable cutout portions adapted to increase the internal space of the back box.

The cutout portions may be adapted to increase the internal space in the plane of the mounting surface. The cutout portions may be provided at the body. Alternatively or in addition, the cutout portions may be provided at the flange member. The cutout portions may extend from the flange member and into the body. The flange member may be substantially square. A cutout portion may be provided at one or more corner regions of the flange member. A cutout portion may be provided at each of the four corner regions of the flange member.

The back box may include one or more removable tabs, each tab being removable to provide a cutout portion.

According to a second aspect of the present invention there is provided an electrical back box for mounting within a substantially circular hole provided in a mounting surface, the back box comprising:

a body having a substantially circular outer profile;

a flange member adapted to contact the mounting surface when the back box is inserted into the hole, thereby preventing further insertion; and

contact means which is movable to contact the rear of the mounting surface, wherein the contact surface area of the contact means is greater than 600 mm ² .

The contact surface area of the contact means may be greater than 1,000 mm ² . The contact surface area of the contact means may be greater than 1,500 mm ² .

The contact means may comprise two or more lugs, preferably two lugs. Each lug may be provided at opposing sides of the body.

Each lug may have a length of about 25 mm. Each lug may have a width of between 22 and 35 mm.

The back box may include one or more existing or formable cutout portions adapted to increase the internal space of the back box. The cutout portions may be adapted to increase the internal space in the plane of the mounting surface. The cutout portions may be provided at the body. Alternatively or in addition, the cutout portions may be provided at the flange member. The cutout portions may extend from the flange member and into the body.

The flange member may be substantially square. A cutout portion may be provided at one or more corner regions of the flange member. A cutout portion may be provided at each of the four corner regions of the flange member.

The back box may include one or more removable tabs, each tab being removable to provide a cutout portion.

The body of the back box may have a depth which is adjustable.

The body may comprise a rear collar and a front collar, the front and rear collars being arranged around a longitudinal adjustment axis of the electrical back box. The body may include a depth adjustment mechanism adapted to allow the longitudinal position of said collars to be adjusted relative to one another in order to adjust the effective depth of the electrical back box.

The depth adjustment mechanism may comprise a plurality of depth adjustment positions such that the rear collar may be retained in a selected longitudinal position relative to the front collar in order to retain a selected effective depth of the resulting electrical back box.

The depth adjustment mechanism may comprise a friction fit or spring biased mechanism. Alternatively, the depth adjustment mechanism may comprise at least a pawl member and an associated ratchet member provided between the front and rear collars. The or each pawl member may be provided on the rear collar, and the or each associated ratchet member may be provided on the front collar. The pawl and ratchet members may be provided on diametrically opposed sides of said collars.

According to a third aspect of the present invention there is provided an electrical back box for mounting within a substantially circular hole provided in a mounting surface, the electrical back box comprising:

at least a rear collar having a substantially circular outer profile;

at least a front collar having a substantially circular outer profile, the front and rear collars being arranged around a longitudinal adjustment axis of the electrical back box;

a depth adjustment mechanism adapted to allow the longitudinal position of said collars to be adjusted relative to one another in order to adjust the effective depth of the electrical back box such that the electrical back box may reside within and at least partially take up the depth of said substantially circular hole.

The depth adjustment mechanism may comprise a plurality of depth adjustment positions such that the rear collar may be retained in a selected longitudinal position relative to the front collar in order to retain a selected effective depth of the resulting electrical back box.

The depth adjustment mechanism may comprise a friction fit or spring biased mechanism.

Alternatively, the depth adjustment mechanism may comprise at least a pawl member and an associated ratchet member provided between the front and rear collars. The or each pawl member may be provided on the rear collar, and the or each associated ratchet member may be provided on the front collar. The pawl and ratchet members may be provided on diametrically opposed sides of said collars. The front collar may be provided with a face plate frame adapted to allow mounting of a switch face plate thereto. The face plate frame may be provided with selectively removable corner tabs which allow a circular face plate to be mounted to the electrical back box when said corner tabs are removed and which allow a rectilinear face plate to be mounted to the electrical back box when said corner tabs are in position. The front collar may include contact means which is movable to contact the rear of the mounting surface. The contact means may comprise at least a pair of selectively replaceable adjustable retaining lugs adapted to clamp against the rear of a mounting surface to retain the electrical back box fixed thereto. The adjustable retaining lugs may be removable and replaceable with alternative adjustable retaining lugs having a greater or lesser length and / or overall surface area in order to facilitate clamping of the electrical back box to a variety of different mounting surfaces.

The contact surface area of the contact means may be greater than 1,000 mm ² . The contact surface area of the contact means may be greater than 1,500 mm ² .

The contact means may comprise two or more lugs, preferably two lugs. Each lug may be provided at opposing sides of the body.

Each lug may have a length of about 25 mm. Each lug may have a width of between 22 and 35 mm.

Embodiments of the present invention will now be described by way of example only, with reference to the following diagrams, in which:- Fig. 1 is a front perspective view of an electrical back in a retracted

configuration; Fig. 2 is a front view of the electrical back box of Fig. 1;

Fig. 3 is a side view of the electrical back box of Fig. 1;

Fig.4 is a top view of the electrical back box of Fig. 1;

Fig. 5 is a rear view of the electrical back box of Fig. 1;

Fig. 6 is a rear perspective view of the electrical back box of Fig. 1;

Fig. 7 is a top view of the electrical back box of Fig. 1 illustrated in a lengthened configuration;

Fig. 8 is a side view of the electrical back box of Fig. 7; and

Fig.9 is a rear perspective view of the electrical back box of Fig. 7.

An electrical back box 10 comprises a front circular collar 12 and a rear circular collar 14 arranged along a longitudinal adjustment axis 16. The front collar 12 is provided with a square facing flange or plate frame 18. The front collar is also provided with a pair of adjustment channels 20 which each allow adjustment lugs 22 to be moved therealong. The rear collar 14 is also provided with adjustment channels 24 and lug insertion apertures 26.

An adjustment mechanism comprising pawl members 28 provided on the rear collar 14 and ratchet apertures 30 provided on the front collar 12 are provided at the top and bottom of the electrical box 10. In the embodiment illustrated four pawl members 28 and four corresponding ratchet apertures 30 are provided. Each pawl member 28 is therefore provided with an associated ratchet aperture 30 such that four longitudinal locking positions are provided in the embodiment shown; however, greater or fewer pawl members and associated ratchet apertures may be provided in order to provide greater or fewer longitudinal locking positions.

In use, a user will first create a circular hole or recess in a mounting surface (such as a wall, floor, skirting board etc.); the hole or recess having a diameter large enough to neatly receive the diameter of the front and rear circular collars 12, 14 therein. A hole /aperture would normally be created in a plasterboard surface and a solid recess would normally be created in a solid wall. In a domestic environment this hole or aperture is typically formed using a drill fitted with an appropriate hole-saw;

however, in a more commercial setting a bespoke boring tool may be utilised.

The depth of the hole or recess created may be selected by the user depending upon requirements. For example, certain switch plates (for example dimmer switches etc.) require a greater depth than others to accommodate the components of the switch plate and the associated wiring within the small dimensions of the back box.

Once a suitable aperture or recess has been formed in the mounting surface, the user adjusts the depth of the electrical back box 10 along the longitudinal axis 16 by pulling the rear collar 14 away from the front collar 12 whilst releasing the pawl and ratchets 28, 30. As the user does this, the pawl members 28 will click down the aperture positions 30 locking the rear collar 14 relative to the front collar 12 with each progressive adjustment. At this stage, the lugs 22 are typically either removed from the back box 10 or reside in parking areas 21 at the rear of collar 14 ready for deployment.

Once the depth of the back box 10 has been adjusted to suit the depth of the corresponding mounting hole or recess, the user can then progress the back box 10 into the mounting surface. Prior to this, selected knockout panels 13 may be removed by the user in preparation for receiving any electrical wires which require to be connected within the back box 10.

With the back box 10 in position within the mounting surface the next installation step carried out is typically dependent upon the nature of the surface to which the back box 10 is being mounted to. For example, if a wooden joist or other solid fixing material is present behind the back box 10 then it may be fixed in position by screws driven through screw holes 15. If no such option is available (e.g. when fixing to the rear of a plasterboard partition wall) it will be necessary to push the lugs 22 from their parking position 21 through the lug apertures 26. The user can then pull the inner root of the lugs 22 in order to slide the lugs 22 along the adjustment channels 20 until the lugs are at or adjacent the rear of the plasterboard. When the user then attaches the switch face plate (not shown) to the back box 10, the attachment screws of the face plate (which typically reside in a standardised position) will engage with the screw holes 17 of the lugs 22 in order to pull the lugs 22 hard up against the rear of the plasterboard thereby creating a increasingly secure fixing of the back box 10 to the plasterboard as the switch plate is screwed onto the back box 10.

The lugs of conventional back boxes have a maximum contact surface area of about 250 mm ² for each lug or 500 mm ² in total. The back box of the invention use lugs having a greater surface area. Each lug has a conventional length of 25 mm. However, each lug extends out further from the body, typically for between 25 to 35 mm. This gives a total surface area of between 1,100 and 1,750 mm ² .

It has been found that using a combination of a circular back box and larger lugs allows the back box to be used even within lath and plaster walls. Since the back box is circular, the aperture can be formed using a hole saw or the like rather than a pad saw and this causes less disturbance and damage to the wall. Also, the larger lugs allow better gripping of the uneven, non-planar rear of the wall. The back box effectively forms a bridge between slats which, after being cut, are only supported at one end.

If desired, and depending upon the nature of the surface to which the back box 10 is to be mounted to, the user may remove the lugs 22 entirely and replace them with longer lugs which have a greater surface area for securing against the rear of the

plasterboard.

The back box 10 includes existing or formable cutout portions that are adapted to increase the internal space of the back box. This allows the back box 10 to be used with any face plate, including the likes of three way switches which include more components at their rear surface. In the embodiment of Figs, 1 to 9, the cutout portions are existing in the sense that they are already present. Each cutout portion extends from the flange and into the body. A cutout portion is provided at each of the four corner regions of the flange. As illustrated in the embodiment of Figs. 10 and 11, the electrical back box 10 may also be provided with a number of additional knockout corner tabs 19. In this embodiment, the cutout portions are formable by the user by removing the tabs.

The above described back box is therefore straightforward to install and provides the maximum amount of space for the connection of cables together and to any switching arrangement as well as providing the back box 10 with a universal quality (since it can be adjusted to accommodate a variety of different depths of recess and can

accommodate switching plates whose rear components are large or small in dimension).

Although particular embodiments of the invention have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims.

It is contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the scope of the invention as defined by the claims. Examples of these include the following: - Although adjustment of the collars 12, 14 along the longitudinal axis 16 is provided in the above described embodiments by way of a ratchet and pawl mechanism, such adjustment may instead be achieved in a number of other ways. For example, a friction-fit or spring-biased telescopic connection could be provided between the front and rear collars.