BACKGROUND 
     The present disclosure relates generally to air conditioning units for use in a hazardous environment where flammable gases or vapors may exist. In particular, the present disclosure relates to air conditioning units which prevent gases from being ignited by encapsulating sparking components, using solid-state switching devices, and/or wiring circuits in such a way that open contacts do not contain enough energy to produce a spark capable of igniting the atmosphere. 
     In many applications, it is necessary to provide air conditioning or refrigeration systems in locations where flammable gases or vapors exist. For example, a worker may be surrounded by atmospheric conditions conducive to danger. An oxygen rich atmosphere might be particularly conducive to flash fire caused by a stray spark. A similar condition could exist in a dust laden atmosphere or in an atmosphere which includes flammable vapors. At such locations, it is necessary to provide protection against the ignition of such flammable gases or vapors, in order to prevent the occurrence of highly undesired explosions. 
     In the prior art, explosion-proofing techniques included creating a purged and pressurized system to create a non-hazardous environment, or adding a large cast explosion proof enclosure to contain any undesired explosions and placing any sparking devices within the explosion proof enclosure. However, these explosion proof techniques were unduly complicated and expensive because purge and pressurization devices required shop air, and large cast explosion proof enclosures are bulky and expensive. Further, these bulky enclosures significantly increased the size of the hazardous location rated air conditioners. 
     SUMMARY OF THE INVENTION 
     The present disclosure includes a compressor overload for use with air conditioning or refrigeration systems in a hazardous location where flammable gases or vapors may exist, comprising: a thermal sensor, at least one overload terminal, a base bracket, a disc, at least one wire configured to attach to the at least one overload terminal, and encapsulation material wherein the encapsulation material forms an air tight cover surrounding the compressor overload. 
     The present disclosure also includes a compressor start relay for use with air conditioning or refrigeration systems in a hazardous location where flammable gases or vapors may exist, comprising at least one relay terminal, at least one wire coupled onto the at least one relay terminal, and encapsulation material wherein the encapsulation material forms an air tight cover completely surrounding the compressor start relay. 
     The present disclosure includes a wiring circuit for air conditioning or refrigeration systems in a hazardous location where flammable gases or vapors may exist, comprising a compressor, a transformer, a high energy circuit, a low energy circuit, a solid state relay wherein a first portion of the solid state relay is configured to connect to the high energy circuit and a second portion of the solid state relay is configured to connect to the low energy circuit, and a line voltage. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a compressor overload. 
         FIG. 2  is a perspective view of the compressor overload of  FIG. 1 , showing the compressor overload enclosed in encapsulating material. 
         FIG. 3  is a schematic wiring diagram of a compressor relay start. 
         FIG. 4  is a perspective view of the compressor relay start of  FIG. 3 , showing the compressor relay start enclosed in encapsulating material. 
         FIG. 5  is a perspective view of a pressure switch with its body wrapped in heat shrink tubing. 
         FIG. 6  is a schematic wiring diagram of a start circuit, shown as prior art. 
         FIG. 7  is a schematic wiring diagram of the start circuit of  FIG. 6 , where a low energy circuit has been added. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “connected,” “attached” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected,” “attached” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
     A compressor overload  10 , a compressor start relay  30  and a pressure switch  50  are each components which can form a part of an air conditioning unit. Any of these components have the potential to create a spark during ordinary use. A spark could lead to an explosion if any of these components are used in a hazardous location where ignitable concentrations of flammable gases or vapors may be present. Therefore, it is desirable to encapsulate these components within an air tight material to prevent any potential sparks from mixing with flammable gases or vapors which may exist in the surrounding environment. 
       FIG. 1  shows one embodiment of a compressor overload  10  having a thermal sensor  12 , overload terminals  14 , a base bracket  16  and a disc  18 . In this embodiment, the disc  18  is configured to be coupled to the base bracket  16 . The disc  18  can be rotated and locked into the base bracket  16 . In one embodiment, wires  19  (shown in  FIG. 2 ) can be attached to the overload terminals  14 . The wires  19  can be coupled to the overload terminals  14  by soldering them onto the terminals  14  or by various other attachment means known in the art. 
     A compressor overload  10  can create a spark during operation, which could cause a potential explosion in a hazardous environment. Therefore it is desirable to contain the sparking components of the compressor overload  10  within an air tight encapsulation material  22  to prevent any potential sparks from coming into contact with nearby flammable gases or vapors.  FIG. 2  shows an embodiment of an encapsulated compressor overload  20 . In this embodiment, components of the compressor overload  10  such as the thermal sensor  12 , overload terminals  14  and disc  18  are completely covered by the encapsulation material  22 . The encapsulation material  22  can also cover a portion of the base bracket  16  and a portion of the wires  19 . 
     Various other combinations can be used where different combinations of components can be enclosed by the encapsulation material  22  as long as the components which are capable of creating a spark are completely contained within the encapsulation material  22 . The encapsulation material  22  forms an air tight cover surrounding the compressor overload  10 . In one embodiment the encapsulation material  22  forms a cylindrical cover over the thermal sensor  12 , overload terminals  14 , base bracket  16  and disc  18 . However various different shapes can be used for the encapsulation material  22  as long as the shape creates an air tight seal over the potential sparking components. The requirement of an air tight seal also applies where the base bracket  16  and wires  19  extend up to or through the encapsulation material  22 . 
     In one embodiment, the bottom surface  24  of the base bracket  16  is not covered by the encapsulation material  22  and sits flush with the encapsulation material  22 . The thermal sensor  12  is located next to the base bracket  16 , which is thermally conductive, to allow the thermal sensor  12  to sense temperature through the bracket  16 . The bottom surface  24  of the base bracket  16  is not covered by any encapsulation material  22  to allow the thermal sensor  12  to sense temperature through the base bracket  16 . 
     In one embodiment, the following steps can be used to encapsulate a compressor overload  10 . A user can take a compressor overload  10  and attach wires  19  to the overload terminals  14  of the compressor. This form of attachment includes but is not limited to direct coupling or soldering. The base bracket  16  and disc  18  can be cleaned with a cleaning agent such as isopropyl alcohol before being coupled together. After cleaning the base bracket  16  and disc  18 , the user can rotate the disc  18  into the base bracket  16  and lock the bracket  16  and disc  18  together via various forms of engagement which are known in the art. In one embodiment, this form of engagement includes a protrusion on the disc  18  engaging an indentation on the bracket  16 . 
     The user can also substantially or completely cover all the electrically live parts of the compressor overload  10  with a silicone sealant which can be flame resistant. An electrically live part is any part which has electricity flowing through it. In one embodiment, this flame resistant sealant has a thickness sufficient to meet the UL 94 V-0 minimum flammability rating which is a standard that classifies plastics according to how they burn in various orientations and thicknesses. The UL 94 V-0 is a plastics flammability standard released by Underwriters Laboratories of the USA. In one embodiment this minimum thickness is 5.4 millimeters. The user can locate or otherwise create a casting or mold in a desired shape for the encapsulation material  22 . In the embodiment shown in  FIG. 2 , the mold has a cylindrical shape but it should be understood to one of ordinary skill in the art that various other shapes can be used as well to suit a user&#39;s needs. 
     After obtaining a mold, the user places the compressor overload  10  and any attached wires  19  inside the mold. The user can then pour liquid encapsulation material into the mold to completely encapsulate the compressor overload  10  and any attached wires  19 . After hardening, the encapsulation material  22  creates an air tight seal around the compressor overload  10  and wires  19  to ensure that any potential spark is completely contained within the encapsulation material  22  and cannot interact with any gases or vapors outside the encapsulation material  22 . In one embodiment, the encapsulation material  22  can be a polyurethane resin and/or can have a thickness of one-quarter inch all around. In another one embodiment, the encapsulation material  22  can be poured to be flush with the bottom surface  24  of the base bracket  16 . 
       FIG. 3  shows a wire diagram of one embodiment of a compressor potential start relay  30  having relay terminals  32 , a first wire  34 , a second wire  36  and a third wire  38 . It should be understood to one of ordinary skill in the art that the compressor start relay  30  is not solely limited to the use of three wires as shown in  FIG. 3 , but can use a varying number of wires. In one embodiment, the first  34 , second  36 , and third  38  wires can be attached to individual relay terminals  32 . The wires  34 ,  36 ,  38  can be coupled to the relay terminals  32  by soldering them onto the terminals  14  or by various other attachment means known in the art. 
     Because a spark can be created during operation of the compressor start relay  30 , it is desirable to contain the sparking components within an air tight encapsulation material  22  to prevent any potential sparks from coming into contact with the nearby flammable gases or vapors.  FIG. 4  shows one embodiment of an encapsulated compressor start relay  40 . In this embodiment, the compressor start relay  30  and relay terminals  32  are completely covered by the encapsulation material  22 . The encapsulation material  22  can also cover a portion of the wires  34 ,  36 ,  38 . The encapsulation material  22  creates an air tight seal over any potential sparking components. While  FIG. 4  shows a boxed shape for the encapsulation material  22 , it is understood that any shape which creates an air tight seal over the potential sparking components can be used. The requirement of an air tight seal also applies where the wires  34 ,  36 ,  38  extend through the encapsulation material  22 . 
     In one embodiment, the following process can be used to encapsulate a compressor start relay  30 . A user can take a compressor start relay  30  and solder or otherwise attach wires  34 ,  36 ,  38  to the individual relay terminals  32  of the start relay  30 . The user can also substantially or completely cover all the electrically live parts of the compressor start relay  30  with a flame resistant sealant such as silicone. In one embodiment, this flame resistant sealant has a thickness sufficient to meet the UL 94 V-0 minimum flammability rating minimum which in one instance can be 5.4 millimeters. Then the user can locate or otherwise create a casting or mold in a desired shape for the encapsulation material  22 . In the embodiment shown in  FIG. 4 , the mold has a boxed shape with a flange at one end, but it should be understood to one of ordinary skill in the art that various other shapes could be used as well. 
     After obtaining a mold, the user places the compressor start relay  30  with wires  34 ,  36 ,  38  inside the mold. The user can then pour liquid encapsulation material into the mold to completely encapsulate the compressor start relay  30  and wires  34 ,  36 ,  38 . The encapsulation material  22  creates an air tight seal around the compressor start relay  30  and wires  34 ,  36 ,  38  to ensure that any potential spark is completely contained within the encapsulation material  22  and cannot interact with any gases or vapors outside the encapsulation material  22 . In one embodiment, the encapsulation material  22  can be a polyurethane resin and can have a thickness of one-quarter inch all around. 
       FIG. 5  illustrates one embodiment of a pressure switch  50  having a body portion  51 , a first wire  52  with a first connector  54 , a second wire  56  with a second connector  58 , heat shrink tubing  60 , and a third connector  62 . It should be understood to one of ordinary skill in the art that the pressure switch  50  is not solely limited to the use of two wires as shown in  FIG. 5 . 
     Because a spark can be created during operation of the pressure switch  50 , it is desirable to contain the sparking components within an air tight tube  60  to prevent any potential sparks from coming into contact with nearby flammable gases or vapors.  FIG. 5  shows one embodiment of an encapsulated pressure switch  50 . In this embodiment, the body portion  51  of the pressure switch  50  is surrounded by tube  60 . The tube  60  can also cover a portion of the wires  52 ,  56 . In one embodiment, a sealant material such as a polyurethane resin can be applied near the first  64  and second  66  edges of the tubing to create an air tight seal. The sealant material creates an air tight seal where the first wire  52 , second wire  56 , and third connector  62  extend past the first  64  and second  66  edges of the tubing  60  respectively. In one embodiment, the sealant material seals the body portion  51 , tube  60 , first wire  52 , second wire  56 , and third connector  62  such that these components all rotate together when any of the portion of the body portion  51 , tube  60 , first wire  52 , second wire  56 , or third connector  62  is rotated. 
     In one embodiment, the following process can be used to encapsulate a pressure switch  50 . A user can take a pressure switch  50  and place heat shrink tubing  60  over a body portion  51  of the pressure switch  50 . The heat shrink tubing  60  should extend past and cover all the components within the body portion  51  which can create a spark. The user can apply heat to the tubing  60  to shrink it down and conform the tubing  60  to the body portion  51  of the switch  50 . The user can also apply a sealant material such as a polyurethane resin near the first  64  and second  66  edges of the tubing  60 . The sealant material should not exceed the first  64  and second  66  edges of the tubing  60  and combined with the tubing  60 , should create a completely air tight seal around the body  51  of the pressure switch  50 . Creating an air tight seal around the body  51  should completely seal off the sparking components within the heat shrink tubing  60  which eliminates the risk that these sparking components could ignite nearby flammable gases or vapors present in a hazardous location. 
     By sealing off the sparking components  10 ,  30 ,  50  individually, a user avoids having to use alternative safeguards such as a purged and pressurized air system to prevent hazardous outside air from coming into contact with a spark. A purged and pressurized air system can be both complicated and expensive. Similarly, a user also avoids having to use an alternative such as building out a large cast explosion-proof enclosure and placing all of the sparking components within this enclosure. Placing all of the potential sparking components in a single enclosure requires reconfiguring the overall size and shape of the air conditioner to accommodate having all the sparking components in one central location. 
     The present disclosure allows a user to seal off each sparking component individually and therefore allows a user to avoid having to install a purged and pressurized air system, thus enabling the user to maintain the same overall size and shape of a non-hazardous location air conditioner. This results in a lower overall cost and creates a compact self-contained cooling device. 
     Another way to provide protection against the potential ignition of flammable gases or vapors is to wire the air conditioner to make use of a low energy circuit where the energy is a function of the voltage and current in a circuit. The low energy circuit is sufficiently low in energy such that it does not contain enough energy to produce a spark capable of igniting the surrounding atmosphere. 
       FIG. 6  illustrates a wiring diagram of an air conditioning unit according to the prior art. In this air conditioning unit, the wiring for the compressor  70  uses high voltage throughout the entirety of its circuit and thus is powered by a high energy circuit. The compressor  70  is directly connected to a compressor start relay  76 , which in turn is connected to a compressor start capacitor  78 . The compressor start capacitor  78  is connected to the compressor  70  which is also wired to a mechanical contactor  80 . The mechanical contactor  80  is directly connected to the line voltage  74 . Thus, the compressor  70  is connected to the line voltage  74  and uses high voltage throughout its circuit. Because the compressor wiring uses high voltage throughout its circuit, there is a potential for a spark to be created in the compressor start relay  76  between connection points  82 ,  84 . To remove the potential for a spark, the compressor wiring can be reconfigured as shown in  FIG. 7 . 
       FIG. 7  illustrates a wiring diagram of one embodiment of an air conditioning unit where a low energy circuit has been introduced into the compressor wiring. That same principles discussed below would also apply to wiring for a refrigeration unit. In this circuit, the wiring for the compressor  170  uses both high voltage and low voltage. The compressor  170  is connected to a first solid state relay  188  and a compressor start relay  176 . The compressor start relay  176  is connected to a second solid state relay  192 . A first side  190  of the second solid state relay  192  is connected to the secondary side of the step down transformer  172  and thus operates on low voltage. However, a second side  194  of the second solid state relay  192  is wired to a start capacitor  178 , which is connected to line voltage  175 , and therefore it operates on high voltage. The line connections between the connection points  182 ,  184  of the compressor start relay  176  and the first side  190  of the second solid state relay  192  all use low voltage and therefore operate on a low energy circuit. 
     The second side  194  of the second solid state relay  192  is connected to the start capacitor  178 , which in turn is connected to the line voltage  175 . Therefore, the second side  194  of the second solid state relay  192  operates on high voltage and a high energy circuit because it is powered by line voltage  175 . 
     By introducing a low energy circuit, the spark potential in the compressor start relay  176  between connection points  182 ,  184  has been removed because these connection points  182 ,  184  are now wired to the secondary side of the step down transformer  172 . In one embodiment, the line voltage  174  on the primary side of the transformer is  115  volts and the low voltage on the secondary side of the transformer  172  is 24 volts. Thus the connection points  182 ,  184  are now wired using low voltage which does not contain enough energy to produce a spark capable of igniting the gases and vapors in the surrounding hazardous environment. 
     In one embodiment, an overcurrent relay  196  is added to the circuit in order to provide protection against excessive currents. To further eliminate the potential for a spark, the mechanical contactor  80  (shown in  FIG. 6 ) has been replaced by a solid state relay  188  which does not create a spark potential. Thus, by introducing a low energy circuit and replacing the mechanical contactor  80  with a solid state relay  188 , the potential for sparking has been significantly reduced. The low energy circuit eliminates the need for any type of encapsulation, explosion-proof enclosure or purge and pressurization device. 
     It will be appreciated by those skilled in the art that while the disclosure has been described above in connection with particular embodiments and examples, the disclosure is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto.
Embodiments of the disclosure provide an encapsulated compressor overload, an encapsulated compressor relay start, an encapsulated head pressure control switch and a wiring diagram for a circuit for air conditioning units which prevent gases from being ignited by means of encapsulating sparking components, use of solid-state switching devices, and/or wiring circuits in such a way that open contacts do not contain enough energy to produce a spark capable of igniting the atmosphere.