EP2206950A1

EP2206950A1 - Heat resistant casing

Info

Publication number: EP2206950A1
Application number: EP10250019A
Authority: EP
Inventors: Peter Anthony Bridgwater
Original assignee: Scolmore International Ltd
Current assignee: Scolmore International Ltd
Priority date: 2009-01-12
Filing date: 2010-01-07
Publication date: 2010-07-14
Also published as: GB2466875A; GB0900420D0; CN201412785Y; GB2466875B; GB201000221D0

Abstract

A heat-resistant casing 10 for an electrical fitting comprises a housing of a self-supporting substantially rigid construction of heat resistant material having a top 11 supporting one or more side-walls 12, the top 11 is provided with at least one aperture, and a first solid fire-resistant intumescent material 18 is positioned within the housing so that when used with an electrical fitting it will be between the interior surface of the top and the electrical fitting. The first solid fire-resistant intumescent material 18 is smaller in area than the interior surface of the top of the housing and is preferably triangular or rectangular.

Description

This invention relates to a new fire resistant casing for use with electrical fittings, particularly for use with lamp holders.
New building regulations require down-lighters fitted into ceilings to be provided with fire hoods to prevent or at least minimise the spread of fire. Various types of fire hood have been proposed which include a fire resistant intumescent material that upon excessive heating (e.g. in the event of a fire) expand to many times their original volume, thus forming a fire barrier to minimise or prevent fire spread. These hoods have been quite successful, but the aim is still to increase the efficiency of the built-in ventilation and fire/heat protection, whilst providing a cost effective and easy to install option. An object of the present invention is to provide a new heat resistant casing (fire hood) which can be supplied already fitted with a lamp holder or other electrical fitting and which in use is efficient at minimising heat build up and also in preventing or minimising fire spread, should that occur. It is known to use a disc of solid fire resistant intumescent material the same size and shape as the interior of the top of a housing ('can'), but this is expensive as the intumescent material itself is costly and there is a great deal of wastage.
According to one aspect of the present invention there is provided a heat-resistant casing for an electrical fitting in which the casing comprises a housing of a self-supporting substantially rigid construction of heat resistant material having a top supporting one or more side-walls, the top is provided with at least one aperture, and a first solid fire-resistant intumescent material is positioned within the housing so that when used with an electrical fitting it will be between the interior surface of the top and the electrical fitting, characterised in that the first solid fire-resistant intumescent material is smaller in area than the interior surface of the top of the housing.
Although reference is made to a 'first' solid fire-resistant intumescent material, there may or may not be a second solid fire-resistant intumescent material in or on the heat-resistant casing.
The housing is usually provided with attachment means for an electrical fitting so that it can be supplied as a 'lamp ready' product. The housing is preferably of substantially circular cross-section and of metal or plastic. The top preferably has a plurality of apertures for ventilation (heat dissipation), passage of electrical cables and attachment means for the first fire resistant intumescent material. The 'free edge' of the side wall, i.e. the side wall remote from the top, preferably has an outwardly extending lip. This lip may be used for attachment of a cover for the electrical fitting. Preferably the housing is further provided with a collar of a second solid fire-resistant intumescent material which extends substantially completely around the exterior surface of the side wall or walls.
Where the electrical fitting is a lamp holder, a cover in the form of a decorative ring can be attached to the lip. The casing is particularly applicable for recessing into a support structure such as a ceiling or wall, especially when the support structure is being constructed.
The intumescent material may be based on graphite or other intumescent materials which upon exposure to extreme heat expand in volume. The thickness of the intumescent material is usually in the range 0.4mm to 6mm, preferably in the range 0.6mm to 2mm and advantageously in the range 0.8mm to 1.5mm. An example of a graphite based material is that supplied by Technical Fibre Products Limited as 'Intumescent Material' and consists of a high temperature Rockwool fibre mat containing easily dispersed foliating graphite bonded in acrylic. Where a second intumescent material is used e.g. as a collar which extends substantially completely around the exterior surface of the side wall or walls, it may be of the same composition as the first intumescent material, or different.
The first intumescent material is usually a single component provided with at least one and advantageously a plurality of apertures. The apertures are for passage of electrical cables and/or for ventilation to dissipate heat that tends to build up in the casing when the electrical fitting is switched on. Preferably the first solid fire-resistant intumescent material is spaced apart from the interior surface of the top so that there is a gap between it and the interior surface of the top of the housing. Such a gap is preferably is in the range 2 to 8 mm, more preferably 2 to 5mm.
In a preferred embodiment a plate is provided to support the first intumescent material, in which case the plate is usually provided with apertures, at least some of which coincide with those of the first intumescent material. The apertures are conveniently circular holes punched through with a suitable tool. The plate is preferably sized to fit snugly within the casing and may then be attached to the interior surface of the top by means of e.g. nuts and bolts. The nuts also serve to maintain the space (where desired) between the interior surface of the top and the first intumescent material supported on the plate. At least one location means is preferably provided to aid location and retention of the first intumescent material in the assembly. For example the location means could be one or more flanges positioned so that the intumescent material fits into a predetermined position. Where a support plate is provided then that may be adapted to have location means e.g. there could be a plurality of upturned portions struck up from the plate by means of a suitable tool. The shape of the first intumescent material is usually straight edged rather than curved and preferably triangular, advantageously an equilateral triangle as this offers the greatest cost saving and minimal waste.
Alternatively it can be square or rectangular. The area of the first intumescent material is preferably less than 75%, more preferably less than 50% and advantageously less than 25% of the internal surface area of the top of the housing.
Where a plate is provided, this may conveniently be used for attachment of the electrical fitting e.g. by means of nuts and bolts. The electrical fitting is preferably positioned within the housing so that it does not touch the internal surface of the side wall or walls.
It will be appreciated that certain features of the invention which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are for brevity described in the context of a single embodiment, may also be provided separately or in any suitable combination.
Embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a schematic view illustrating examples of shapes of the first intumescent material and the reduced wastage when using a straight-edged component of triangular or square shape according to the present invention in place of the known circular full-sized disc.
Figure 2 is a perspective top view of a casing according to the present invention.
Figure 3 is a schematic view of the casing of Figure 2, partially cut away to show the triangular shaped intumescent material.
Figure 4 is a top perspective schematic view of a second embodiment of the present invention in which the intumescent material is square.

Referring now to Figure 1, the first picture shows how much intumescent material is wasted when a full circle is cut from a square sheet to fit completely over the inner surface of the top of a housing. The second and third pictures show how much less intumescent material is used when an equilateral triangular or a square of intumescent material is cut to fit into a circular housing. In addition, because the triangle and the square have straight edges, there is far less wastage of intumescent material when these shapes are cut from a large sheet of such material.
When cutting a circular disc from a square, 21% of the material is wasted. This is constant regardless of size (assuming the circle reaches the edges of the square as shown).When using an equilateral triangle as shown, where all points touch the outer circle, 58% of material is saved when compared to a large circular disc. A square with all points touching the circle (as shown) saves 36% of material when compared to a large circular disc. It would be possible to use a rectangle, depending on the position of the ventilation holes, but it is not possible to give a percentage figure for the material usage as the size of the rectangle cannot be defined in relation to the diameter of the housing.
Referring now to Figures 2 and 3, a heat resistant casing 10 comprises a cylindrical pressed steel housing consisting of a top 11 supporting a side wall 12. The side wall 12 has a lip 13 onto which may be clipped a cover (not shown) by means of spring clips 14a & 14b which are attached by a bracket 15 to the centre of the top 11. A collar 16 of solid fire resistant intumescent material surrounds the side wall 12. The collar 16 is 25mm high and 1 mm thick and is glued in place. Within the housing is a steel plate 17 supporting a 1 mm thick layer of solid fire resistant intumescent material 18 in the shape of an equilateral triangle and positioned on the plate 17 by means of three locating flanges 19. Plate17 and layer 18 have corresponding apertures. There is a gap between the top 11 and layer 18 which is chosen to be in the range 2 to 5mm. The plate 17 is held in place by 4 nuts and bolts 20, which also keep the gap consistent. A pressed steel lamp holder (not shown) can be attached to plate 17 by means of nuts and bolts. In the event of a fire, the solid fire resistant intumescent material 18 expands to 9 times its volume, filling the gap between the top 11 and plate 17 and filling the aforementioned apertures. This expansion helps to prevent the fire from spreading e.g. to an upper floor when the housing is recessed into a ceiling. Also, the collar 16 of solid fire resistant intumescent material expands to nine times its volume, filling the space between the housing and the surrounding structure e.g. the ceiling. This expansion helps to prevent the fire from spreading.
Referring to Figure 4, the housing is of exactly the same construction as shown in Figures 2 and 3 but with a square intumescent material disc rather than a triangle. Using a square component allows the introduction of more apertures for cabling and/or ventilation.

Claims

A heat-resistant casing for an electrical fitting in which the casing comprises a housing of a self-supporting substantially rigid construction of heat resistant material having a top supporting one or more side-walls, the top is provided with at least one aperture, and a first solid fire-resistant intumescent material is positioned within the housing so that when used with an electrical fitting it will be between the interior surface of the top and the electrical fitting, characterised in that the first solid fire-resistant intumescent material is smaller in area than the interior surface of the top of the housing.
A heat-resistant casing according to claim 1 in which at least one location means is provided to aid location and retention of the first solid intumescent material.
A heat-resistant casing according to claim 2 in which the location means comprises one or more flanges.
A heat-resistant casing according to any preceding claim in which the first solid intumescent material is straight edged.
A heat-resistant casing according to claim 4 in which the first solid intumescent material is triangular.
A heat-resistant casing according to claim 5 in which the first solid intumescent material is an equilateral triangle.
A heat resistant casing according to claim 4 in which the first solid intumescent material is square.
A heat-resistant casing according to claim 4 in which the first solid intumescent material is rectangular.
A heat-resistant casing according to any preceding claim in which the area of the first solid intumescent material is less than 75% of the internal surface area of the top of the housing.
A heat-resistant casing according to any preceding claim in which the area of the first solid intumescent material is less than 50% of the internal surface area of the top of the housing.
A heat-resistant casing according to any preceding claim in which the area of the first solid intumescent material is less than 25% of the internal surface area of the top of the housing.