Regulation 3.2 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant: Clipsal Australia Pty Ltd Actual Inventors: Chris Hutchings Philip Andrew Clark Address for Service: C/- MADDERNS, First Floor, 64 Hindmarsh Square, Adelaide, South Australia, Australia Invention title: AN ELECTRICAL ENCLOSURE AND A GASKET FOR AN ELECTRICAL ENCLOSURE The following statement is a full description of this invention, including the best method of performing it known to us.
FIELD OF THE INVENTION The invention relates to electrical enclosures and components for electrical enclosures, in particular electrical enclosures that protect against the ingress of both dust and moisture. BACKGROUND TO THE INVENTION Electrical enclosures that protect against the ingress of both dust and moisture are required for industrial switch gear. Such switch gear is often required to operate in harsh industrial environments. For instance industrial switch gear generally satisfies an international protection rating or ingress protection rating ("IP" rating). Many application require IP56 protection which may be defined as "dust protected" and protected against "powerful water jets". IP56 is simply an example of a level of protection that may be required for an electrical enclosure. Other requirements include IP66 and IP22 for example. Electrical enclosures are typically manufactured to a quality standard within a factory environment. The electrical enclosures are then packaged and sold for installation in the field by electricians. When installing an IP56 electrical enclosure for example, an electrician is required to terminate electrical wiring to the enclosure and is required to seal the enclosure by sandwiching a gasket between a base and a lid of the electrical enclosure. The lid is typically secured to the base using screws. As the electrician tightens the screws, the gasket is compressed thereby sealing the lid against the base so as to prevent the ingress of both dust and moisture into the cavity formed between the lid and the base. A difficulty with prior art electrical enclosures is that there is a high degree of reliance on the skill of the electrician to correctly assemble the components so as to obtain an adequate seal between the base, the gasket and the lid. If screws holding the lid to the base are over tightened, excessive compression of the gasket can occur in local areas and distortion of the lid can occur. Furthermore, excessive stresses can occur at or near the screws which can cause cracking, either at the point of installation or possibly months or years later. In harsh environments, chemicals can attack areas of high stress leading to cracking and failing of the enclosure allowing the ingress of dust and or moisture into the enclosure. It is an object of the invention to provide an improved gasket for an electrical enclosure. 0 It is a further object of the invention to provide an improved electrical enclosure. SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a gasket for an electrical enclosure, the 5 gasket providing ingress protection against both dust and moisture, the gasket mountable between a lid and a base, the gasket including: a gasket frame; and 2 a gasket seal, the gasket seal connected to the gasket frame, whereby, in use, a hard stop is provided by sandwiching of the gasket frame between the base and the lid and the gasket seal presents sealing faces to the lid and the base. 5 In one form the gasket frame includes a peripheral T-shaped flange, the T-shaped flange having a top and a stem, the top of the T-shape flange having end faces that provide a hard stop sandwichable between the lid and the base. In one form the gasket seal extends from either side of the stem of the T-shaped flange to provide a pair J of opposed sealing faces disposed beyond the end faces of the T-shaped flange, in use the gasket seal compressed such that the sealing faces are aligned with the end faces of the T-shaped flange. The gasket may be a co-moulded or over-moulded single piece gasket 5 According to a second aspect of the invention, there is provided a single piece co-moulded gasket for an electrical enclosure, the gasket providing ingress protection against both dust and moisture, the gasket mountable between a lid and a base, the gasket including: a first portion having a first elastic modulus; and a second portion having a second elastic modulus, the second elastic modulus lower than the first ) elastic modulus such that when a given compressive stress is applied, the second portion is strained at least three times as much as the first portion. In one form the second portion is strained at least ten times as much as the first portion. According to a third aspect of the invention, there is provided an electrical enclosure for sealing an electrical component from both dust and moisture, the enclosure including: a base; a lid; and a gasket mountable between the lid and the base, the gasket including a gasket frame and a gasket 0 seal, the gasket seal connected to the gasket frame, whereby the base the lid and the gasket are mutually shaped such that compression of the gasket seal is controlled by a hard stop provided by sandwiching of a portion of the gasket frame between the base and the lid. 5 In one form the gasket frame has a first elastic modulus and the gasket seal has a second elastic modulus, the second elastic modulus lower than the first elastic modulus such that when a given compressive stress 3 is applied, the gasket seal is strained at least three times as much as the gasket frame. In one form the gasket seal is strained at least ten times as much as the gasket frame. 5 In one form the gasket frame includes a peripheral T-shaped flange, the T-shaped flange having a top and a stem, the top of the T-shape flange having end faces that provide a hard stop sandwichab le between the lid and the base. In one form the gasket seal extends from either side of the stem of the T-shaped flange to provide a pair ) of opposed sealing faces disposed beyond the end faces of the T-shaped flange, in use the Lasket seal compressed such that the sealing faces are aligned with the end faces of the T-shaped flange. In one form the top of the T-shaped flange, in use, is positioned to form a continuous barrier between the lid and the base, thereby affording a degree of protection to the gasket seal. Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. These embodiments are illustrative, and are not meant to be restrictive of the scope of the invention. ) DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENT ON A preferred embodiment of the invention as illustrated in the accompanying representatioIs in which: Figures Ia & lb are exploded isometric views of an electrical enclosure according to an em bodiment of the invention. 3 Figure 2a is an isometric view of the gasket shown in figures I a and I b. Figure 2b is an isometric view of a gasket according to an alternative embodiment of the i vention. Figure 3 is a plan view of the gasket frame of the gasket shown in figure 2a. Figures 4a and 5a are cross-sectional views taken through section lines 4a -4a and 5a-5a illustrated in figure 3. 0 Figures 4b and 5b are close up views of the portions of the gasket frame indicated by arrows 4b and 5b of figures 4a and 5a respectively. Figure 6 is a plan view of the gasket shown in figure 2a. Figures 7a and 8a are cross-sectional views taken through section lines 7a-7a and 8a-8a ill strated in figure 6. 5 Figures 7b and 8b are close up views of the portions of the gasket indicated by arrows 7b and 8b of figures 7a and 8a respectively. Figure 9 is a front view of the enclosure of figures 1a and l b. 4 Figure 10 is an exploded side view of the enclosure of figure Ia. Figure I I is a cross-sectional view taken through the section lines 11-Il indicated in figure 9. Figures 12 and 13 are detailed views of the portions of the enclosure as indicated by arrows 12 and 13 respectively in figure 11. Referring to figures I a and I b, an electrical enclosure 10 for sealing an electrical component or components from both dust and moisture is shown. The enclosure includes a base 20, a lid 30 and a gasket 50. The base 20, the lid 30 and the gasket 50 are mutually shaped such that compression of the gasket seal 70 is controlled by a hard stop provided by sandwiching of a portion of the gasket frame 64 J between the base 20 and the lid 30. The electrical enclosure 10 shown in figures Ia and I b enclose a switch portion 34 and a power socket portion 35. The switch portion 34 receives a switch knob (not shown) with an O-ring seal. The power socket is covered by a flap (not shown) having an over-moulded gasket. Electrical wiring for these 5 components is protected from the ingress of dust and moisture by the assembled enclosure. In other embodiments of the invention, not shown, the enclosure may house electrical, electronic or other components that need to be protected from the ingress of dust and moisture for instance. The enclosure 10, with a simplified lid 30, may be used as a terminal box. ) Referring now to figure 2a, the gasket 50 is shown in more detail. The gasket is preferably a single piece co-moulded or over-moulded gasket. The gasket frame 60 is made from a plastics material having a first elastic modulus and comprises 10% talc filled copolymer polypropylene. Other suitable materials may be used instead. Co-moulded or over .3 moulded with the gasket frame 60 is a gasket seal 70. The gasket seal 70 is made from a material that is pliant. In the embodiment illustrated, the material used for the gasket seal 70 comprises oil extended thermoplastic styrenic rubber modified polypropylene compound. The gasket seal 70 has a second elastic modulus, the second elastic modulus lower than the first elastic modulus such that when a given compressive stress is applied, the gasket seal is strained (compressed) at least three times as much as the 0 gasket frame. An alternative gasket to that shown in figure 2a is shown in figure 2b. The gasket shown in figure 2a may be referred to as a "two-gang" gasket, whereas the gasket shown in figure 2b may be referred to as a "one-gang" gasket. The "one-gang" gasket of figure 2b is the same general construction to that shown in '5 figure 2a. Again, the gasket 50 has a gasket frame 60 made from a stiff plastics material and co-moulded or over-moulded with the gasket frame 60 and the gasket seal 70. Again, the gasket seal 70 is made from a material that is pliant. 5 Turning now to figures 3, 4a and 4b, 5a and 5b, the gasket frame 60 of the gasket 50 is more easily visualised (as it is shown without the co-moulded gasket seal 70). 5 Figures 4a and 4b provide a cross-sectional view through section lines 4a-4a illustrated in figure 3. Section 4a-4a is taken through screw holes 69. The construction of the gasket 50 generally is apparent from figure 4a and figure 4b is a magnified view of the region indicated by arrow 4b on figure 4a. From figure 4b it can be seen that the gasket frame 60 includes a peripheral T-shaped flange 63, the T-shape flange 63 having a top 64 and a stem 65. The top 64 has end faces 66 and 67 that provide a hard stop J sandwichable between the lid 30 and the base 20. This sandwiching is clearly shown in figures I I and 12. Referring now to figures 5a and 5b taken through section lines 5a-5a illustrated in figure 3, it can be seen that the gasket frame includes an inner locating portion 68. This inner locating portion 68 is shown in figure 13 captured between a leg 32 of the lid and the peripherary 39 of the lid 30. In other embodiments 5 of the invention, the leg 32 may be omitted. Now referring to figures 6, 7a and 7b, 8a and 8b, the gasket 50 is shown in full. In particular, it can be seen from figures 7b and 8b that the gasket seal 70 is connected to the gasket frame 60. In one embodiment of the invention, the connection is by virtue of a co-moulding process. In other embodiments J of the invention, the gasket frame and gasket seal may be manufactured as separate components and then subsequently bonded together. Referring again to figures 7b and 8b, it can be seen that the gasket seal 70 extends from either side of the T-shaped flange 63 to provide a pair of opposed sealing faces 74 and 75 that are disposed beyond the end .3 faces 66 and 67 of the T-shaped flange 63. Now referring to figures I1, 12 and 13, the gasket 50 and gasket seal 70 can be seen in use. In particular, it can be seen that the gasket seal 70 is compressed such that the sealing faces 74 and 75 shown in figures 7b and 8b respectively are compressed such that they are aligned with the end faces 66 and 67 of the T 0 shaped flange (in figures 12 and 13, the actual compression is not shown, instead compression is represented by overlapping cross-sections). The degree of compression is controlled by the geometry shown in figure 12. In the embodiment shown the compression of the gasket seal is approximately 30%. '5 Referring again to figures I1, 12 and 13, it can be seen that the electrical enclosure 10 provides an enclosed portion 90 that is sealed to IP 56 standard against the ingressed so the ingress of dust or 6 moisture. The hard stop provided by the peripheral T-shaped flange 63 as described above provides for controlled gasket seal deformation. This reduces the reliance on the skill of the electrician to correctly assemble the base 20, the gasket 50 and the lid 30 together. The electrician can tighten the screws 41 that extend through holes 3 1 in the lid 30, holes 51 in the gasket 50 and into holes 21 within the base 20 until 5 the top 64 of the peripheral T-shaped flange 63 is sandwiched between the base 20 and the lid 30. Thus, the electrician is less likely to over tighten the screws which in turn means that cracking, either at the time of installation or possibly months or years later is must less likely. Furthermore, distortion of components is less likely greatly improving the performance of the gasket and minimising the possibility of any ingress of dust or moisture into the enclosure. A further benefit of the gasket 50 shown in figure 2a when installed between the base 20 and lid 30, is that the top 64 of the T-shaped flange 63 provides a degree of protection to the gasket seal 70. More specifically, it can be seen from the drawings that the top 64 of the peripheral T-shaped flange 63 provides a continuous barrier between the lid 30 and the base 20. Should the enclosure 10 be exposed to 5 water jets or abrasion from dust, grit or other particles, the seal 70 is protected by the gasket frame 60. This lessens the likelihood of failure of the seal 70 and hence lessens the likelihood of ingress of dust or moisture into the enclosed portion 90 of the electrical enclosure 10. The electrical enclosure 10 illustrated in the drawings as described above uses the gasket illustrated in 3 figure 2a. In other applications, an electrical enclosure of a squarer shape may be used with the gasket shown in figure 2b. Similarly, larger enclosures may be employed for some applications incorporating two gaskets of the type shown in figure 2b alongside one gasket of the type shown in figure 2a for instance. .3 The enclosure 10 shown in figure Ia and I b may be sold partially pre-assembled. For instance the screws 41 may be positioned through the lid 30 and the gasket 50 so that the electrician only has to attach the lid (with screws and gaskets already attached) onto the base 20. The gasket 50 can be constructed to retain the screws 41 prior to their final assembly into the base 20. 0 It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 7