Abstract:
A motor control compartment provides an air flow chamber at the rear thereof and mounts the solid state switches on heat sinks that are positioned in the air flow. An apertured support plate separates the interior of the compartment from the air flow chamber and allows additional space for supplemental control equipment.

Description:
BACKGROUND OF THE INVENTION 
     Electrical equipment enclosures such as those described within U.S. Pat. No. 4,683,517 entitled &#34;Integrated Lighting Panelboard and Wiring Gutter Assembly&#34; which contain electrical switches are often custom assembled at the point of manufacture to accommodate the size and number of switches contained therein. 
     U.S. Pat. No. 5,151,842 entitled &#34;Switchboards and Panelboards Having Interlock and Load Selection Capabilities&#34; describes such enclosures when used to contain electronic circuit breakers and the like. 
     A more recent example of an electrical equipment enclosure is found within U.S. Pat. No. 5,424,911 entitled &#34;Compact Motor Controller Assembly&#34;. This patent describes motor starters and contactors used to efficiently start and stop industrial rated electric motors. One such motor starter is found within U.S. Pat. No. 5,341,080 entitled &#34;Apparatus and Three Phase Induction Motor Starting and Stopping Control Method&#34;. 
     In such state-of-the-art motor control devices, solid state switches such as SCRs for example, are often employed to controllably switch the motor current to provide smooth motor starting and stopping function. Since the SCRs become heated upon current transfer therethrough, heat sinks in the form of large metal blocks of copper, aluminum and their alloys are required to protect the SCRs from overheating. 
     Other types of electrical control equipment, such as relays, contactors, control power transformers and the like are often required within the motor control compartment, the motor compartment is oversized to accommodate the heat sinks. 
     One purpose of the invention is to provide a modular motor control compartment that provides a separate controlled air-flow compartment for the heat sink to free-up the area within the compartment adjacent the motor control unit to facilitate space as well as to accommodate electrical connection with the motor controller unit. 
     SUMMARY OF THE INVENTION 
     A motor control compartment provides an air flow chamber at the rear thereof and mounts the solid state switches on heat sinks that are positioned in the air flow. A support plate separates the interior of the compartment from the air flow chamber and allows additional space for supplemental control equipment. Additional space is thus acquired within the compartment for supplemental electrical control equipment. Placement of the supplemental control equipment on the support plate provides conduction cooling to the supplemental control equipment as well. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a compact electrical equipment compartment according to the invention; 
     FIG. 2 is a top perspective view of a motor control unit mounted on a support shelf and arranged on top of a heat sink; 
     FIG. 3 is a front perspective view of the compact electrical equipment compartment of FIG. 1 with the motor control and support shelf in isometric projection; and 
     FIG. 4 is a side plan view of the electrical equipment compartment of FIG. 1 attached to a support wall with arrows depicting air current flow. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A motor control compartment 10 is shown in FIG. 1 and includes a metal enclosure 11 that includes a top 12, bottom 13 and opposing sidewalls 14, 15. An air channel 16 is provided in the rear of the enclosure and continues from the top slot 16A to the bottom slot 16B, as indicated and includes side vents 8A, 8B for added ventilation efficiency and to allow inspection. The top and bottom slots are usually covered with a wire mesh (not shown) to prevent egress of dust and materials within the air channel. The compartment is wall-mounted by means of the top and bottom flanges 12A, 13A respectively. Cable access knockouts 9A, 9B are provided on the top and bottom 12, 13 for receiving the load and line cables (not shown) which connect with the corresponding line and load terminals arranged on the top and bottom of the motor starter unit 19. The motor starter unit is similar to that described within the aforementioned U.S. Pat. No. 5,341,080 and includes switches 20 within the transparent faceplate 21 for setting the motor operating characteristics. Access to the associated motor (not shown) is deterred by means of the door 17 mounted to the sidewall 14 by means of hinges 18, as indicated. 
     The floor support 25 is shown in FIG. 2 to consist of a rectangular plate that is folded to define a front wall 26 with a pair of opposing sidewalls 27, 28 for added rigidity. The plate can be fabricated from steel or an aluminum alloy with beryllium to provide excellent thermal conductivity along with good structural support. The motor starter unit 19 is first attached to the heat sink 30 and the floor support 25 is positioned thereover by passing the motor starter through the rectangular aperture 26A formed in the front wall. The heat sink is fabricated from a solid aluminum block with a plurality of fins 31 formed therein to present a large specific surface for transfer of heat away from the SCRs 29 contained within the motor starter unit. 
     With the motor starter unit 19 positioned on the floor-support 25, the arrangement is then placed in the enclosure 11 within motor control compartment 10 in the manner shown in FIGS. 3 and 4 wherein the top and bottom tabs 34, 35 extending from the top 12 and bottom 13 abut against the opposite surface of the front wall 26 to accurately position the input and output terminals 23, 24 (shown also in FIG. 1) adjacent the apertures 9A, 9B respectively and position the sidewalls 27, 28 to define the air channel 16 for the heat sink 30 as shown in FIG. 1. 
     The operation of the cooling efficiency of the enclosure 11 is best seen by now referring to FIG. 4 where the enclosure is shown attached to a support wall 32 by means of screws 33. With the door 17 closed, and the motor starter unit 19 operational, the heat generated within the motor starter unit transfers via the heat sink 30 to the ambient air by virtue of the air flow depicted by arrows from the bottom slot 16B of the air channel 16 out to the top slot 16A as well as out the side vents 8. The positioning of the heat sink 30 in the air flow stream diverts the heat away from the internal components resulting in a measured decrease in the ambient temperature generated therein and, in some applications, allows the substitution of a lower power-rated SCR. 
     It is noted that additional electrical control equipment can also be included within the interior of the enclosure 11 along with the motor starter unit 19 such as the circuit breaker 36 and overload relay 37, as indicated in phantom. The mounting of the additional control equipment directly onto the surface of the front wall 26 of the floor support 25 allows the heat generated within the additional control equipment to exit through the support out to the air channel 16. In some applications, the provision of the perforated metal screens (not shown) insure that insects and air-borne debris do not enter the air channel along with the cooling air. 
     A modular electrical equipment enclosure having a defined air flow channel has herein been described. The provision of large heat sinks outside the interior of the enclosure within the defined air channel is found to allow additional electrical equipment to be contained within the enclosure without requiring a larger geometry or forced air cooling by means of circulatory fans.