Abstract:
A modular power distribution system is provided for distributing power within an equipment rack. One particular power distribution system has a control unit that is mounted proximate a rack including a power input for receiving power from a power source located outside the rack. The control unit includes a power converter for converting the received power to an output electrical power, and a plurality of power outlets for providing an electrical connection to the control unit and outputting the output electrical power. This particular power distribution system also includes an extension means mounted proximate the rack and having an electrical power input for input of electrical power to the extension means and a plurality of power outlets adapted to couple with and distribute electrical power to conducting elements that electrically connect the extension means to the mounted equipment. This particular power distribution system further includes an electrical power cable connected to one of the power outlets in the control unit and to the electrical power input of the extension means.

Description:
PRIORITY  
       [0001]     This patent application is a continuation of, and claims priority from, a patent application Ser. No. 10/185,530 titled “Modular Power Distribution System For Use In Computer Equipment Racks” filed Jun. 28, 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates, in general, to power distribution and distribution systems, and more particularly, to a modular power distribution unit for use in distributing power within the limited space of an equipment cabinet or rack, such as a computer equipment rack or a data storage cabinet.  
         [0004]     2. Relevant Background  
         [0005]     In the computer industry, mass storage systems and other computer systems typically include numerous multi-shelf cabinets or racks each holding multiple devices or encloses, such as servers, disk drives, and other computer devices. These racks or rack systems are ideal for modular projects and are designed to accept standard sized devices having relatively standard power requirements and communication connections. Generally, the outer case includes an aluminum or steel framework fitted with covers and a series of connectors at the rear from which the devices or modules derive their power and exchange communication signals. The individual modules include a supporting chassis or housing that slides into the rack and is supported on guides, such as clip-in glides. Racks and rack systems are inherently flexible but are often expensive which drives users and rack makers to efficiently use space within the rack or cabinet.  
         [0006]     Each rack or cabinet typically only has a limited amount of space that is defined by or urged into shelves. The shelves or shelf locations are configured to allow a device enclosure or module or other components to be plugged into and supported within the rack. Typical rack configurations call for 14 shelves although more shelves may be provided such as up to 24 or more shelves. If shelves are arranged vertically, a typical cabinet may have 14, 24, 32, or some other number of shelves that each occupy a certain amount of rack space, such as 3 retma(U) which is a standard mounting unit increment.  
         [0007]     In practice, such as data centers, data storage, and the like, the racks are often densely packed with devices, such as servers each requiring a primary power supply and a backup power supply for redundancy. For example, one arrangement uses up to 14-3U server enclosures in a rack requiring up to 28-750 watt power supplies. In another rack configuration, 21-2U servers are installed in a rack with 42-500 watt primary and redundant power supplies. A major challenge facing rack and equipment designers is how best to serve dense equipment users so as to provide increased power distribution while efficiently using the space within the rack to reduce cable clutter and connection and supply confusion. In other words, it is desirable to reduce the amount of space required for power distribution units (PDUs) (e.g., typically, a plurality of electrical receptacles to which electrical plugs of power cords can be connected and which are supplied by an inlet A/C power source) and power cords from the PDUs to the devices on the rack shelves to thereby free up rack U-space for more modules or enclosures.  
         [0008]     Existing forms of power distribution require large volumes of cabinet or rack space as numerous PDUs are provided and often mounted in the rack that reduces the available shelves or U-space for computer or other desired components. For example, current PDU support requirements often call for as many as four to six 24 amp PDUs per rack, which leads to some rack configurations being limited when a maximum number of PDUs have been installed in the rack In addition to the space required for the PDUs, large volumes of rack space may be required for the large number of power cords and other devices required to connect the PDUs to the individual devices or loads on the shelves. Often, an enclosure or device is located on a shelf which is relatively distant from the closest PDU which requires a long power cord to be snaked through the rack to the enclosure or device. The number of the cables and PDUs increases deployment complexity and can cause connection problems and mistakes. Additionally, after installation is completed, later expansions or modifications to the rack and power distribution arrangements are difficult to successfully implement.  
         [0009]     Hence, there remains a need for an improved method and system for distributing power within an equipment rack or cabinet that requires less U-space, reduces the number and lengths and cost of connecting power supply cords used in racks (Le., provides improved cable or cord management), is simple to customize, to install, and upgrade or later modify, and reduces the total deployment cost  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention addresses the above discussed and additional problems by providing a modular power distribution system for use in distributing power to devices, modules, and/or enclosures mounted within equipment racks or cabinets. The power distribution system includes two basic building blocks: a core or control unit and one or more (and, typically 2 or 4) extension sticks or bars. The modular architecture allows a rack designer to custom configure a rack power distribution system based on their particular computer or other equipment needs and power availability, which minimize cable clutter and confusion and increases available rack space.  
         [0011]     Generally, the modular power distribution system concentrates central features of typical power distribution Systems (e.g., a main power switch, circuit breakers, load groups, and power-on indication) into the core unit that is configured to be mounted at a remote location within the rack or cabinet enclosure. The housing of the core unit is this, such as IU or less, and include clips orb for mounting vertically on a side of the rack (e.g., a OU mounting) or horizontally (e.g., a 1U or less mounting). The extension bars include a number (e.g., 1 to 8 connections are provided in some embodiments) of AC power outlets, receptacles, connectors, cord segments, or other devices for connecting enclosures, modules, or devices in the rack to a power source. The extension bars include clips or other fasteners for mounting onto one corner support of the rack which avoids using rack U-space for the extension bars while also enabling positioning of the bars at nearly any height within the rack and typically, near the rack positions or shelves of the devices being powered to reduce the need for long lengths of power supply cords and extend outlets along the entire or any desired portion of the length of the rack.  
         [0012]     In operation, the core unit provides protected outputs that feed power to multiple high current outlets in the extension bars that can be used for connecting the high current loads, e.g., the enclosures, modules, or devices mounted on the shelves of the rack, to an acceptable power supply or source. The extension bars each connect directly to the core unit via a flexible power supply cord. The extension bars effectively locate the “fanning out” of the AC power in the rack closer to the loads and eliminates many power supply cords that were required in previous distribution arrangements. A wide range of capacities may be provided according to the invention (such as 16 to 40 amps devices) and numerous outlets may be provided in each modular power distribution system, such as 32 outlets with the used of 4 extension bars each having 8 AC power outlets (which in turn may be any of several industry standard connector families or be short power leads that connect directly to the load when it is desired to eliminate power cords).  
         [0013]     More particularly, a power distribution system is provided for distributing power to electrical or computer equipment in an equipment rack. The system includes a control unit mounted within the rack having a power input electrically connected to a power source (such as with a cable or hardened to an AC power source or facility source) and a converter for converting the input power from the source to a power supply required by the rack equipment The control unit includes a housing on which a plurality of power outlets or connections are mounted for providing an electrical connection to the control unit and for distributing the converted power supply to the equipment An extension bar is mounted within the rack typically adjacent one of the corner supports of the rack. The extension bar includes a power inlet and is connected via an electrical conductor or power cord to one of the power outlets of the control unit The extension bar includes a number of power outlets (such as up to or more than 8) adapted for electrical connection to power supply lines (cords or hardwiring) from the rack equipment The control unit housing typically includes one or more brackets for rigidly mounting the housing to the corner supports of the rack. In some embodiments, the control unit is mounted vertically in a OU mounting with the thin (i.e., less than about 1U) cross-section of the housing positioned between two adjacent corner supports. In other embodiments, the control unit is mounted horizontally in a less than 1U mounting with the thin cross-section of the house position horizontally between the corner supports. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a functional block diagram of a modular power distribution system according to the present invention;  
         [0015]      FIG. 2  is a partial perspective view of one embodiment of a modular power distribution system, similar to  FIG. 1 , installed in a typical equipment rack or cabinet showing the side mounting arrangement of the core or control unit;  
         [0016]      FIG. 3  is a perspective view similar to that of  FIG. 2  illustrating another embodiment of a modular power distribution system showing the “1U” or horizontal mounting arrangement of the core or control unit;  
         [0017]      FIG. 4  is a front perspective view of a core unit, as would be used in the systems of  FIGS. 1-3 ;  
         [0018]      FIG. 5  is a rear perspective view of the core unit of  FIG. 4 ;  
         [0019]      FIG. 6  is functional block diagram of equipment in a rack illustrating the use of a pair of control units of the invention to provide primary and secondary or backup power to four enclosures, such as servers; and.  
         [0020]      FIG. 7  is a functional block diagram similar to  FIG. 6  illustrating the use of a pair of modular power distinction unit of the invention to distribute power to three enclosures, similar to  FIG. 6 , but also providing a number of other rack options or devices. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     The present invention is directed toward modular power distribution systems for use in equipment racks, such as those typically utilized in the computer and data storage industries, and rack designs incorporating such modular systems. The modular systems are unique in utilizing two building blocks to allow ready field configuration and placement of power outlets within a rack. The first building block is control unit that provides the connecting point to a power supply outside the rack and includes a number of control and distribution components such as main power switch, circuit breakers, load groups, and remote power monitoring and management (such as via a network like the Internet or other communication network). The control unit has a thin housing with mounting brackets that allow the unit to be mounted either in a vertical or side mounting in the rack (“a OU mounting”) that does not use any rack space or a horizontal or in rack mounting (“a 1U mounting”) that uses a small portion of the rack space. The second building block is a set (e.g., 1 to 4 or more) of extension bars or sticks that are connected to the control unit and include a number (such as 1 to 8 or more) of power outlets, receptacles, and the like to distribute power to numerous locations in the rack. Similar to the control unit, the extension bars include housings with clips or brackets that allow the extension bars to be mounted on vertical structural members (e.g., corner supports) of the rack at varied heights to place the outlets near the rack loads, e.g., enclosures, modules, and other rack-mounted devices and equipment The modular system address the problem of cable management by significantly reducing the number of cords and cables required and reducing the lengths of cables in the rack which improves cooling in the rack and frees up additional rack U-space.  
         [0022]     More specifically,  FIG. 1  illustrates a modular power distribution system  100  in functional block form as the system  100  may be integrated into an equipment rack  110 . The equipment rack  110  may be any of a number of widely available equipment racks used in the computer and electronics industry, such as the Compaq Rack 9000 and 10000 Series. The rack  110  generally includes space or shelves on or in which equipment modules or enclosures are positioned, with an industry standard being 3 retmas equaling 1U. An important design configuration form any racks is attempting to utilize all or most of the rack U-space or shelves with functional equipment (such as computer servers, controllers, and the like) and not with support or peripheral equipment, such as power distinction devices and power supply cables.  
         [0023]     With this space requirement in mind, the power distribution system  100  includes a cool or core unit  120  which centralizes numerous power distribution, power distribution and load monitoring, and control functions within a single device and includes one or more power supply sticks or extension devices that provide power from the control unit  120  to a number of loads or enclosures (not shown in  FIG. 1 ) mounted throughout the rack  110 . As will be discussed with reference to  FIGS. 2-5 , the control unit  120  typically includes a relatively small housing (such as IU or less thickness) and mounting brackets compatible with standard racks  110 . The combination of small size and mounting bits allows the control unit  120  to be mounted in numerous locations within the rack  110  in a vertical or side arrangement (“0U mounting) between two corner supports of the rack  110  that takes up no or little rack U-space or in a horizontal or shelf arrangement (“1U mounting”) that takes only 1U or less of rack U-space.  
         [0024]     The control unit  120  provides a power supply function within the rack  110 . The unit  20  is connected to power source  140  by power cord or cable  144 . The control unit  120  functions to brings power into the rack  110  from power source  140  (e.g., any of numerous power sources used in the computer equipment and data storage industries) and then converts the power removed from power source  140  to a power supply useful or demanded by loads in the rack  110 . To this end, the control unit  120  includes converter  22  to convert the input power (such as 30 to 50 amp AC) on cable  144  for distribution on power supply cables  152 ,  156 ,  162 ,  172  to extension bars  150 ,  154 ,  160 ,  170 .  
         [0025]     The control unit  120  provides protected outputs that feed power via the converter  122  to multiple current outlets (typically, high current outlets) on the control unit  120  that can be used to connect to individual high current loads (not shown in  FIG. 1  but see  FIG. 6 ) or to the tension bars  150 ,  154 ,  160 ,  170  via flexible cords  152 ,  156 ,  162 ,  172 , respectively. Each extension bar  150 ,  154 ,  160 ,  170  includes multiple power outlets (e.g., AC power outlets) to locate the “fanning out” of the AC power closer to the load and eliminate multiple long runs of individual power cords. The power outlets may be any of numerous industry standard connector families or be short power leads that can connect directly to the load to eliminate the need for power cords. As will discussed with reference to  FIG. 2 , the extension bars  150 ,  154 ,  160 ,  170  are configured for mounting on corner supports of the rack  110  with clips or other brackets and may be mounted at user-selected heights to allow ready customization of the power distribution system  100  and to place the extension bars, and therefore power outlets, near to loads within the rack  110 .  
         [0026]     The number of extension bars  150 ,  154 ,  160 ,  170  may be four, as shown, or any other useful number (such as 1, 2, 3, 4, 5, or more) as long as the total current does not exceed the maximum allowable current draw or current rating of the control unit  120 . Similarly, the number of power outlets can vary, and in one embodiment, 8 outlets are provided on each extension bar  150 ,  154 ,  160 ,  170 , which provides  32  outlets (or support for 32 loads) with one control unit  120 . A receptacle fan-out device  178  may be connected to an extension bar, such as bar  170 , to enable additional loads to be supported by the power distribution assembly  110 . The device  178  may be any accepted power supply device, such as typically plug-in outlet centers, power outlet strips, UPS products, and the like.  
         [0027]     To fulfill this power supply or distribution function, numerous configurations can be used for the control unit  120  and converter  122  and for the extension bars  150 ,  154 ,  160 ,  170  (as well as the number of such bars or sticks). The embodiments may range from lower input power density (such as a 16 amp input with 1 or 2 expansion bars) up to high input power density (such as 3-phase input supporting up to 6 extension bars). With this broad range of inputs and outputs, the following are just a few exemplary (but not limiting) examples of how the power distribution function may be provided in a system  100 . One embodiment is designed to connect low voltage (i.e., 100 to 127 AC voltage) power sources and/or directly into a facility outlet (i.e., power source  140 ) via cord  144  and a single input on unit  120  (such as a NEMA L5-30P or the like) and four outputs (such as four IEC320-C19 outlets at 12 amps each). This embodiment typically has a relatively low maximum current or current rating (such as 24 amps) with the output being up to 32 outlets such as 8 NEMA 5-15 or other outlets on the bars  150 ,  154 ,  160 ,  170  with maximum outlet and bar currents (such as 12 amp maximum per outlet and 12 amp maximum per bar).  
         [0028]     In another embodiment of system  100 , a higher input voltage (such as 200 to 240 AC voltage) is input via cord  144  from power source  140 , which is typically the facility input, and having four outputs (such as four IEC320-C19 outlets at 12 amps each). In this embodiment, the maximum through current may again be set at 24 amps with each extension bar  150 ,  154 ,  160 ,  170  having up to 8 IEC 320 C-13 or other outlets with maximum outlet and total extension bar currents (such as 10 amps per outlet and 12 amps per bar). In another embodiment, the maximum current through the control unit  110  is set at 32 amps with single input (such as an IEC 309-32A) provided in the control unit  110  with four outlets for connecting to power supply cords  152 ,  156 ,  162 ,  170  and each extension bar  150 ,  154 ,  160 ,  170  having 8 outputs or outlets (such as 8 IEC 320 C-13 or similar outlets). In another example, the control unit  110  is designed to hardwired via cord  144  to the power source  140  (such as the facility input or a high voltage UPS). The input connection on the unit  110  then may be a field wired terminal and the maximum current for the unit  110  may be higher, such as 40 amps and the input voltage higher, such as 200 to 240 volts AC. In this example, the extension bars  150 ,  154 ,  160 , and  170  may not be identical with three having 8 outlets (such as 8 IEC 320 C-13 outlets with a maximum outlet current such as 10 amps) with a particular maximum bar current (such as 12 amps) and with the fourth bar having fewer outlets (such as 4) with but with higher current rating (such as 4 IEC 320 C-19 outlets having a 12 amp rating). In this manner, loads having differing power input requirements can be mounted within a single rack  110  and supplied power effectively with a control unit  120  with differently configured extension bars  150 ,  154 ,  160 ,  170 . These are just a few examples of the configurations for the power distribution system  100  and are not intended to be limiting but to demonstrate the flexibility of the system  100  to distribute power at varying locations and to differing types of loads within the rack  110 .  
         [0029]     As shown, the control unit  120  includes an overload protector  124  and output circuit breakers  126  to more effectively provide the power distribution function in the system  100 . More particularly, the overload protector  124  and output circuit breakers  126  provide input overcurrent protection, surge protection, and load segment output overcurrent protection. The overload protector  124  may be any device or circuit that, for example, disconnects the control unit  120  from the power source  140  when the current or voltage becomes excessive (over design limits for the control unit  120 ). The output circuit breakers  126  are provided to open the circuit to the outlet receptacles or connections to the extension bars  150 ,  154 ,  160 ,  170  via cords  152 ,  156 ,  162 ,  172 , and the number and rating of the output circuit breakers  126  may vary to suit the allowable current in the bars  150 ,  154 ,  160 ,  170  (e.g., in 12 amp embodiments of the bars, 15 amp or smaller circuit breakers may be provided for each outlet receptacle in the control unit  120 ). Although not shown, the control unit  120  may include line fail-over switching devices or circuits along with multiple utility feeds for redundant power supply or source configurations (e.g., by adding an additional power source  140  and source line  144 ).  
         [0030]     In addition to rack power distribution functions, the control unit  120  in some embodiments is configured to facilitate a number of remote monitoring and/or remote management or operation functions. Generally, such remote monitoring and monitoring functions may include load segment control (e.g., on/off control), automatic or manual staggered startup of each output from the control unit  120 , line status monitoring, line voltage measurements, power consumption monitoring, and other desired management and monitoring functions. An operator or monitor can view the results of such monitoring and remotely operate the control unit  120  from remote monitoring and control node  190  (such as a typical computer device with I/O devices such as keyboards, graphical user interfaces, and the like, with a processor and memory, and a monitor). Operator node  190  is linked to the control unit  120  via the communication network  180 , e.g., any digital data communications network, wired or unwired, such as the Internet, a local area network (LAN), a wide area network (WAN), and the like, and communication links  182  and  186 . Alternatively, local management via the user node  190  may be provided with a direct connection (such as at a serial interface  132  at the control unit  120  to monitoring and/or management cards in the unit  120 ).  
         [0031]     A communication interface  132  is provided at the control unit  120  to handle input and output functions and to facilitate communication with the user node  190 . For example, the communication interface  132  may be a Web or Internet Protocol (P) interface and the user node  190  may include a Web browser for accessing and communicating with the communication interface  132 . Communications over the network  180  can be implemented using simple network management protocol (SNMP) or other useful protocols that facilitate management applications (such as those that would be operating on node  190 ) to query or command management agents on the control unit  120  (such as those embodied in the remote monitoring unit  128  and/or the remote management unit  130 ).  
         [0032]     The remote monitors unit  128  is provided to monitor a number of parameters during the operating of the control unit  120 . For example, the remote monitoring unit  128  may include measurement sensors for sense line voltages at outlets or in lines  152 ,  156 ,  162 ,  172  to extension bars  150 ,  154 ,  160 ,  170  and in response, to communicate or transmit a signal(s) to the remote monitoring and management node  190  via communication interface  132 . Sensors may also be provided to measure line status or on/off status of the lines  152 ,  156 ,  162 ,  172  and power consumption on these lines  152 ,  156 ,  162 ,  172  to measure operations at the extension bars  150 ,  154 ,  160 ,  170  and connected loads or rack equipment. Again, these operating measurements are communicated to the node  190  via the communication device  132 .  
         [0033]     The remote management unit  130  provides operating management functions for the control unit  120  including local (or automatic control) and remote control functions including distributing power in response to commands from the node  190  (or at an interface on the unit  120  (not shown)). The automatic controls may include staggered setup of each output or extension bar  150 ,  154 ,  160 ,  170 . The remote management features may include intelligent segment control such as remotely providing or terminating power to one or more of the extension bars  150 ,  154 ,  160 ,  170 . More specifically, the remote management commands for the outlets may include configuration of each of the outlets of the control unit  120  (such as via SNMP and interface  132 ), immediate on, sequenced on, delayed on, immediate off, and reboot (e.g., turning an outlet off and then back on immediately or with delays). Shutdown commands may also be issued to the control unit  120  to turn off all outlets. Other useful management commands may be issued by the node  190  and processed by the remote management unit  130 , such as a cancel command to stop action on the most recent command and an override command to cancel a previous command and replace it with a new command.  
         [0034]      FIG. 2  illustrates one physical implementation and mounting arrangement for a modular power distribution system in a rack As shown, a modular power distribution system  200  is installed in a rack  210  in the vertical or OU-mounting arrangement to limit the amount of rack U-space being used by the system  200  (e.g., to consume no or very little rack U-space). The rack  210  is a standard equipment rack with side walls having a row or strip  216  of mounting slots  216  and with corner supports  214  also including mounting holes or slots. As shown, the control unit  220  has its substantially planar housing  221  arranged vertically (i.e., with a plane passing through the housing being substantially parallel to the side walls of the rack  210 ). Mounting brackets or clips  226 ,  228  are provided on the ends of the housing  221  of the control unit  220  for rigidly clipping to or mating with the holes or slots in the corner supports  214 . While shown in a generally upper position within the mack or cabinet  210 , the control unit housing  221  can be mounted at any useful position or height within the rack  210 . Outlet on/off switches  222  are provided on the housing  221  and a control unit on/off switch  224  is also included to allow local, manual control of the power distribution to the outlets of the housing  221  to which the power supply cords  252 ,  256 ,  262 , and  272  are connected at housing  221 . Power is supplied to the control unit  220  via inlet power cord  244  which is connected to a power source or supply (not shown) external to the rack  210 .  
         [0035]     The illustrated system  200  fans out power distribution within the rack  210  by including four power extension bars  250 ,  254 ,  260 ,  270  that are connected to control unit  220  with power supply cords  252 ,  256 ,  262 ,  272 . The power extension bars  250 ,  254 ,  260 ,  270  may be configured similarly to the bars  150 ,  154 ,  160 ,  160  with similar maximum currents, with outlets or receptacles (such as with 8 outlets or receptacles as shown) or cord segments, and other described features. The bars  250 ,  254 ,  260 ,  270  can be mounted at any position or height within the rack  210  (typically, adjacent planned loads or equipment positions on the shelves). The configuration of the bars  250 ,  254 ,  260 ,  270  allows mounting within the rack  210  without consuming rack U-space as the bars  250 ,  254 ,  260 ,  270  have generally square or rectangular cross sections that are similar in size to the corner supports  214 , such that the bars  250 ,  254 ,  260 ,  270  either extend only slightly beyond the corner supports  214 , are coplanar, or are actually recessed from the surfaces of the corner supports  214 . As shown for bar  270 , mounting clips or brackets  274 ,  276  are provided on the ends of the bar  270  for rigidly mounting the bar  270  to the row  216  of mounting holes or slots on the side wall of the rack  210 , which provides flexibility in the positioning of the bar  270  at nearly any position within the rack  210 . As shown, cable management is significantly improved with only four short supply cables  252 ,  256 ,  262 ,  272  being used to supply 32 outlets (at least in this embodiment) from which  32  loads can be supplied with relatively short jumpers.  
         [0036]      FIG. 3  illustrates some of the mounting and configuration flexibility provided by the modular power distribution Systems of the invention A power distribution system  300 , with several similar components, is shown installed in the rack  210 . As shown, the housing  221  of the control unit  220  is mounted horizontally in the rack  210  with mounting clips  226 ,  228  being used to mount the housing  221  to corner supports  214 . The housing  221  is relatively thin so as to take up as little rack U-space as possible while still providing desired functions (such as 1U, 0.5U, or less thickness). In one embodiment, the housing  221  is about 17.5 inches by about 1.62 inches by about 13 inches (width by height or thickness by depth). The depth may be maintained at less than half the depth of the rack  210  to allow two control units  220  to be mounted back to back, horizontally, which is useful in modular power distribution systems that utilize two control units  220  to distribute power in a rack  210 . Alteratively, when two units  220  are installed in a single rack  210 , the units  220  may be mounted adjacent to each other but top to bottom or be mounted in a spaced apart fashion at two differing locations within the rack  210 . In the system  300 , only two extension bars  260 ,  270  are provided and are attached to the control unit  220  by cords  262 ,  272 , respectively. Of course, more or fewer extension bars may be utilized in the system  300  (or in system  200 ).  
         [0037]      FIGS. 4 and 5  illustrate one embodiment for a control core unit  420  (such as would be used in systems  100 ,  200 , and  300 ). As shown, the control unit  420  includes a housing  421  that is rectangular in shape and has a thickness or height, H that is selected to allow the control unit  420  to be mounted either in a vertical or horizontal mounting (as described in  FIGS. 2 and 3 ) without requiring much if any rack U-space. In most embodiments, the thickness or height, H, is less than or equal to about IU and in some embodiments is less than about 0.5U to allow stacking of 2 control units on a single shelf The thinness of the housing  421  enables 1U or less horizontal mounting, which leaves desirable rack U-space for other equipment in a rack.  
         [0038]     As shown, a main ON/OFF switch  424  is provided for shutting down the control unit  420  along with a main indicator light  430  for indicating when power is provided to the unit  420  and when the switch  424  is placed in the ON position An outlet switch or circuit breaker (such as a  15  amp circuit breaker)  422  is provided for each power outlet of the unit  420  (in this case  4  outlet switches  422  are provided to control, and in the case of circuit breakers to overcurrent and surge protect, outlets  450 ). Although not shown, indicator lights may be provided for each of the outlet switches  422 . Power is supplied to the control unit  420  by an attached input power cord (which may, in some embodiments, be replaced by hard wiring directly to a facility input)  444  which is connected to the housing  421 , such as by a protective earth bonding screw  445 . The power cord  444  is also attached to a power source or supply (such as a facility AC power source). Power outlets  450  are provided to allow connection with standard power cords to extension strips or bars, and the number and type of outlets  450  may be varied to practice the invention. As shown, four outlets  450  (such as 4 IEC C19 outlets) are provided to support power distribution to up to four extension bars. In remote monitoring and/or management embodiments (such as that shown in  FIG. 1 ), a plug-in for an interface connection is provided for a communication signal cable to a network and/or remote monitoring and control node, e.g., a SNMP or other connection.  
         [0039]      FIGS. 6 and 7  illustrate two power distribution systems  600  and  700  that illustrate the flexibility of the invention in allowing a user to configure power distribution in differing, modular ways to meet their rack power needs. In a rack in the data storage and other industries, a typical power system block diagram may call for a primary and a backup AC input to three, four, or more high current loads.  
         [0040]     In  FIG. 6 , two control units  620  and  630  without extension bars are used to provide the AC transfer switch function or power distribution (from primary and backup power sources not shown) to the loads. As shown, a modular power distribution system  600  includes a rack  610  in which a primary control unit  620  and a backup control unit  630  are mounted (either vertically or horizontally at a desired height in the rack  610 ). Four enclosures (such as servers or other computing or data storage device)  640 ,  650 ,  660 ,  670  are also mounted in the rack  610  and are configured for redundant power supplies with primary and backup inlets  642 ,  644 ,  652 ,  654 ,  662 ,  664 ,  672 ,  674 , respectively. During normal operations, the primary control unit  620  distributes power to the enclosures  640 ,  650 ,  660 ,  670  via power supply cords  624  that are connected individually to the power outlets  622  of the primary control unit  620  and to the primary inlets  642 ,  652 ,  662 ,  672 . The backup control unit  630  supplies backup power via power supply cords  634  that are connected individually to the outlets  632  and the backup inlets  644 ,  654 ,  664 ,  674  on the enclosures  640 ,  650 ,  660 ,  670 .  
         [0041]     An alternate modular power distribution system  700  is shown in  FIG. 7  that demonstrates how the combined use of control units with extension bars is useful for fanning out pluggable or other power supplies within a rack without cable confusion or loss of rack U-space. As shown, the system  700  includes a rack  7   10  in which three enclosures, such as high current loads including servers and the like,  740 ,  750 ,  760  are mounted along with a number of other rack devices  770 . The high current loads  740 ,  750 ,  760  are provided redundant power directly from a primary control unit  720  and a backup control unit  730 . This is achieved by connecting primary inlets  742 ,  752 ,  762  via cables  726  to outlets  724  on the primary control unit  720  and by connecting backup inlets  744 ,  754 ,  764  via cables  736  to outlets  734  on the backup control unit  730 .  
         [0042]     Significantly, the other rack devices  770  are also provided redundant power via extension strips  780  and  790  that are connected via cables  726 ,  736  to outlets  724 ,  734  on primary and backup control units  720 ,  730 . The extension strips  780  and  790  have outlets  784 ,  794  (such as 8 outlets or receptacles) that are then connected by jumpers or hard wiring to the other rack devices  770 . Through the use of extension strips  780 ,  790 , a number of enclosures  740 ,  750 ,  760  and other rack devices  770  can be powered from one or two control units  720 ,  730  with minimal cables, with reduced cable run lengths, and with increased available rack U-space (as the control units  720 ,  730  can be vertically mounted in a OU mounting or horizontally mounted in a 1U or less mounting and as the extension strips  780 ,  790  are corner mounted so as to not use an rack U-space).  
         [0043]     As can be appreciated, the modular characteristics of the combined use of a core control unit with one or more sticks or strips significantly enhances flexibility in growth (e.g., larger capacity and/or more features) and provides simplified maintainability. Regarding flexibility, once a power distribution system is installed a user is able to upgrade the features and/or capacity in the control unit by simply replacing the unit without modifying or replacing other portions of the system, such as the extension strips which can remain in place connected to their loads. The extension strips or sticks can be unplugged from the core or control unit and the control unit can be replaced with a control unit of greater capacity (e.g., a 16 amp unit can be upgraded or changed to a 24, 32, or 40 amp core or vice versa) or a control unit with more or different control or power distribution features or functionality, such as one with remote monitoring and management features. In contrast, existing power distribution systems typically require replacement of the entire power distinction system and wiring the new system. Maintainability is improved because a defective part can simply be replaced without disturbing other components of the power distribution systems of the present invention. For example, if an extension slick becomes defective, only that extension stick needs to be replaced or paired and if a core maintains, the core can be readily replaced without the need for rewiring power distribution to loads or to the sticks.  
         [0044]     Although the invention has been described and illustrated with a certain degree of particularity, the present disclosure has been made only by way of example and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention. A system according the invention, such as system  100  of  FIG. 1 , may include 2 or more control units within a single rack  110  each connected to extension bars to quickly increase the number of power outlets within a rack, to increase the modularity of power distribution control and distribution, and to allow differing loads to be powered within a single rack (i.e., through the use of 2 different control units with different output characteristics). In some embodiments of the invention, a single type of extension bars is utilized while in some arrangements it is useful to provide 2 or more differing extension bars, such as extension bars with different numbers and/or types of outlets or including cord segments for supplying power to various loads in a rack. While specific voltages and/or currents have been described, the modular power distribution system are by nature voltage independent and worldwide compatible. The power distribution system typically conforms with power distribution industry standards, e.g., conform to standards such as the National Electrical Code (e.g., NFPA 70) and the Standard for Safety of Information Technology (e.g., UL 1950, Standard for Safety of information Technology Equipment, and/or IEC950).