Automatic transfer switch with programmable display

We claim:

1. Display apparatus, comprising:

M display means each with X parallel input ports for converting X bits of parallel input data to a display symbol;

first shift register means with X parallel output ports, a serial input port and a separate serial output port for receiving at said serial input port said X bits in series and for providing said X bits of serially entered data simultaneously, one each at each of said X parallel output ports;

second shift register means with N parallel output ports and a serial input port which is connected to said serial output port of said first shift register means for receiving N bits of serial data therefrom and for providing N bits of serially entered data simultaneously, one each at each of said N parallel output ports;

X bit parallel data bus means communicating with said X parallel output ports, and with said X parallel input ports of each of said display means for delivery of said X bits of parallel input data to all of said M display means simultaneously;

each of said M display means having a separate enabling means which is interconnected with a combination of said N parallel output ports for being enabled thereby to display said symbol as a function of the occurrence of a coded combination of enabling bits on said N parallel output ports; and

formatting means serially interconnected with said serial input port of said first shift register means or supplying a serial digital word of data comprising said N bits and said X bits in series to said first shift register means, wherein said N bits are serially passed therethrough to said second shift register means wherein said N bits contain only one coded combination of said enabling bits per said word for said N out ports so that only a predetermined one of said M display means is enabled per said digital word to display said symbol associated with said X bits.

2. The combination as claimed in claim 1 wherein said N bits are independent from said X bits in said digital word.

3. The combination as claimed in claim 1 wherein said formatting means supplies M of said serial digital words for a message, wherein a different one of said M display means is enabled for each said digital word.

4. The combination as claimed in claim 3 wherein the residual display time for each of said M display devices is sufficiently long and the time between delivery of each said digit word to said display devices is sufficiently short for each display device to display substantially simultaneously so that said message is displayed substantially at one time.

5. The combination as claimed in claim 1 comprising Z indicator means each independently actuable by the presence of a digital bit of predetermined state at the input thereof;

said second shift register means having a separate serial output;

third shift register means having Z parallel output ports and a serial input port which is connected with said serial output port of said second shift register means for receiving said Z digital bits of serial data therefrom for providing said Z digital bits of serial entered data simultaneously one each at each of said parallel output ports, each of said Z indicator means being interconnected at the input thereof with one of said latter parallel output ports; and

said serial digital word additionally comprising Z bits, wherein said Z bits are passed serially through said first shift register means and said second shift register means to said third shift register means to be presented simultaneously on each of said Z parallel output ports thereof so that those digital bits of said Z digital bits which are of said predetermined state will actuate said indicator means.

6. The combination as claimed in claim 1 wherein M=16.

7. An electrical transfer switch, comprising:

microprocessor means for performing a control function;

M display means each with X parallel input ports for converting X bits of parallel input data to a display symbol;

first shift register means with X parallel output ports, a serial input port and a separate serial output port for receiving at said serial input port said X bits in series and for providing said X bits of serially entered data simultaneously, one each at each of said X parallel output ports;

second shift register means with N parallel output ports and a serial input port which is connected to said serial output port of said first shift register means for receiving N bits of serial data therefrom and for providing N bits of serially entered data simultaneously, one each at each of said N parallel output ports;

X bit parallel data bus means communicating with said X parallel output ports and with said X parallel input ports of each of said display means for delivery of said X bits of parallel input data to all of said M display means simultaneously;

each of said M display means having a separate enabling means which is interconnected with a combination of a portion of said N parallel output ports for being enabled thereby to display said symbol as a function of the occurrence of a coded combination of enabling bits on said N parallel output ports; and

said microprocessor means being serially interconnected with said serial input port of said first shift register means for supplying a formatted serial digital word of data associated with the status of said transfer switch and comprising said N bits and said X bits in series to said first shift register means, wherein said N bits are serially passed therethrough to said second shift register means, wherein said N bits contain only one coded combination of said enabling bits per said word for said N output ports so that only a predetermined one of said M display means is enabled per said digital word to display said symbol associated with said X bits.

8. The combination as claimed in claim 7 wherein said N bits are independent from said X bits in said digital word.

9. The combination as claimed in claim 7 wherein said microprocessor means supplies M of said serial digital words for a message concerning said status of said transfer switch, wherein a different one of said M display means is enabled for each said digital word.

10. The combination as claimed in claim 9 wherein the residual display time for each of said M display devices is sufficiently long and the time between delivery of each said digital word to said display devices is sufficiently short for each display device to display substantially simultaneously so that said message is displayed substantially at one time.

11. The combination as claimed in claim 7 comprising Z indicator means each independently actuable by the presence of a digital bit of predetermined state at the input thereof;

said second shift register means having a separate serial output;

third shift register means having Z parallel output ports and a serial input port which is connected with said serial output port of said second shift register means for receiving said Z digital bits of serial data therefrom for providing said Z digital bits of serial entered data simultaneously one each at each of said parallel output ports, each of said Z indicator means being interconnected at the input thereof with one of said latter parallel output ports; and

said serial digital word additionally comprising Z bits, wherein said Z bits are passed serially through said first shift register means and said second shift register means to said third shift register means to be presented simultaneously on each of said Z parallel output ports thereof so that those digital bits of said Z digital bits which are of aid predetermined state will actuate said indicator means.

12. The combination as claimed in claim 11 wherein said indicator means comprises light emitting diodes.

13. The combination as claimed in claim 7 wherein M=16.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The subject matter of this invention relates generally to automatic transfer switches (ATS) and more particularly to microprocessor-controlled automatic transfer switches.

FIELD OF THE INVENTION

Automatic transfer switch devices are described, for example, in U.S. Pat. No. 3,936,782 issued Feb. 3, 1976 to Moakler et al. and entitled "Automatic Transfer Switch" and U.S. Pat. No. 4,189,649 issued Feb. 19, 1980 to Przywozny et al. entitled "Control Panel For Automatic Transfer Switch". Examples of automatic transfer switches and control devices associated therewith are also described in the following brochures:

"WESTINGHOUSE TRANSFER SWITCHES," SA-10915 by the Westinghouse Electric Corporation, Low Voltage Breaker Division.

"ENGINEERING DATA AUTOMATIC TRANSFER SWITCH," Bulletin ATS-100A, Russelectric, Inc., May, 1984.

"ZENITH ZTS TRANSFER SWITCHES," Bulletin 0-5021 (REV. 2), Zenith Controls, Inc.

"AUTOMATIC TRANSFER SWITCHES," Bulletin SP-44, Square D Company.

"POW-R-TRAN.TM. SOLID STATE AUTOMATIC TRANSFER CONTROLLER", Catalog Section 31-550, Dec. 6, 1976, Westinghouse Electric Corporation, Distribution Equipment Division.

Automatic transfer switches are devices that switch a power source for a load from a primary to a secondary source automatically or after manual switch operation for any number of important reasons. Automatic transfer systems are often found in hospitals, subways, schools, airports, office buildings and other commercial structures equipped with secondary power sources. Basically, automatic transfer systems come in either of two different types. One utilizes a double-throw contactor device while the other type utilizes circuit breakers as the primary switching devices. Furthermore, some kinds of automatic transfer switches systems utilize relay logic exclusively in the control portion thereof. Other types of automatic transfer switch systems utilize solid-state circuit devices to replace the relay devices. In addition, there are automatic transfer controllers which can be used in conjunction with separate automatically operated circuit switching devices such as circuit breakers, or fused or unfused switches. The controller supplies the intelligence to these primary switching devices when automatic transfer of load from one source to another becomes necessary. None of the known automatic transfer switch systems use microprocessor control. It would be advantageous to find an automatic transfer switch or switch system which utilized microprocessor control.

It is known to utilize microprocessor control in other types of circuit systems or devices such as motor control apparatus. An example of such a device is described in U.S. Pat. No. 4,453,117 issued June 5, 1984 to R. T. Elms et al. and entitled "Motor Control Apparatus with Short Term Undervoltage Motor Mode Saver".

It would be advantageous to have a simple microprocessor-controlled automatic transfer switch controller which could be universally utilized either the contactor type of system or the circuit breaker type of system.

It would also be advantageous to have a microprocessor-controlled automatic transfer switch which has a readout device or display which is fast and provides a wide range of information about the status of the automatic transfer switch and control device and which is useful in conjunction with a programmable input device for displaying the status of the automatic transfer switch system.

SUMMARY OF THE INVENTION

In accordance with the invention, an automatic electrical transfer switch is taught which utilizes a microprocessor for performing a control function There are also provided M separate display cells each having X parallel input ports for converting X bits of parallel input data to a display symbol. There is provided a first shift register with X parallel output ports for providing the X bits of serial data simultaneously, one at each of the X parallel output ports, a serial input port and a separate serial output port. There is also provided a second shift register with N parallel output ports and a serial input port which is connected to the serial output port of the first shift register for receiving N bits of serial data therefrom and for providing N bits of serially data simultaneously, one each at each of the N parallel output ports. There is an X bit data bus communicating with the X parallel output ports and with the X parallel input ports of each of the display cells for delivery of the X bits of parallel input data to each of the display cells simultaneously. Each of the display cells has a separate enabling terminal which is interconnected with a portion of the N parallel output ports of the second shift register for being enabled to display a symbol on one cell at a time. The microprocessor is serially interconnected with the input terminal of the first shift register for supplying a formatted serial word of data associated with the status of the transfer switch. The formatted word comprises N bits and X bits in series. The N bits are utilized by the second shift register to determine which of the cells display the X bits of coded display information.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the invention, reference may be had to the preferred embodiment thereof shown in the accompanying drawings in which

FIG. 1 shows a switchboard or switchgear cabinet with an automatic transfer switch and its controller disposed therein;

FIG. 2 shows a detailed view of the controller front panel for the controller of FIG. 1;

FIG. 3 shows a schematic representation of an automatic transfer switch controller system partially in block diagram form for utilization with an electrically tripped circuit breaker system;

FIG. 4 shows an embodiment similar to that of FIG. 3 for a simplified system;

FIGS. 5A through 5H and 5J through 5L show a schematic block diagram of the main controller of the embodiments of FIG. 3 and FIG. 4;

FIGS. 6A through 6D show a schematic representation of the front panel of the controller of FIG. 3 and FIG. 4;

FIGS. 7A and 7B show a schematic representation of the option board of FIG. 3;

FIG. 8 curves A through F show a timing diagram of the pulse arrangements and charging current and voltage for the ranging means of the embodiments of the present invention; and

FIG. 9 shows a family of curves representing the ranging factors for the ranging device of the embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and FIG. 1 in particular, a switch gear cabinet 10 is shown. Switchgear cabinet 10 has a transfer switch controller 12 which includes as part thereof a mechanical mode selector switch 14 and a controller front panel 16.

Referring now more particularly to FIG. 2 that portion of the transfer switch controller 12 of FIG. 1 in the region of the mode selector switch 14 and the controller front panel 16 is shown in greater detail. The mode selector switch 14 may include a control switch handle 17 which can be moved to anyone of three positions: OFF, MANUAL or AUTO, the use of which will be described hereinafter. The controller front panel 16 may include a 16-character controller read out display 18 which may include readout devices which cooperate to display messages and other information. There is also a key switch 20 which is utilized for placing the controller 12 in either the OPERATIONAL mode or PROGRAM mode. There is provided a STEP switch which is utilized to change the input information for the front panel display 18. A number of settable circuit parameters may be changed as a result of manipulation of the switches entitled RAISE and LOWER. In addition, there are five light emitting diodes which may report the status of circuit breakers and power sources controlled and utilized by the transfer switch. Green light emitting diodes entitled SOURCE 1 AVAILABLE and SOURCE 2 AVAILABLE indicate the availability status of either of two separate sources of electrical power. Red light emitting diodes entitled MAIN 1, TIE and MAIN 2 indicate the status of appropriate circuit breakers (illumination means closed) the interconnection scheme of which will be shown and described hereinafter. In the upper right portion of the front panel 16 is a LOCK OUT RESET switch, the use of which will be described in more detail hereinafter.

Referring now to FIG. 3 a schematic block diagram of the controller 12 is shown with interconnection to various circuit control devices and to sources of power and associated circuit breakers as described previously. In the preferred embodiment of the invention the source of electrical power SOURCE 1 (sometimes called the normal source N) having three phase lines A, B and C is shown on the left. On the right is shown a second source of electrical power SOURCE 2 (sometimes called the emergency source E) having three corresponding phase lines A, B and C. To the right of SOURCE 1 is a circuit breaker entitled MAIN 1 and to the left of SOURCE 2 is a circuit breaker entitled MAIN 2. In the embodiment of the invention of FIG. 3 a load LD1 is connected to the right of the circuit breaker MAIN 1 and a load LD2 is connected to the left of the circuit breaker MAIN 2. Intermediate the loads LD1 and LD2 is a TIE breaker. In this embodiment of the invention there is provided an OPTION BOARD 22 which is interconnected electrically with the main controller 12 by way of the connectors J1 on the option board and J12 on controller 12 and the interposed eight lead cable 24. Also provided on the main controller 12 are connectors J5 and J6 each of which have four associated input terminals for interconnection with cables 26 and 28 respectively for monitoring the phase voltage status of the sources SOURCE 1 and SOURCE 2. There is also provided on the controller 12 a connector J8 which is utilized for interconnecting the controller 12 with the front panel 16. An auxiliary connector J9 designated AUX may also be present. Disposed on the controller 12 is a terminal board TB1C having terminals 1 through 15 and a terminal board TB2C having terminals 1 through 15. Likewise, on the option board 22 there is a terminal board TB1O having terminals 1 through 16. The interconnection of the terminal board TB1C, TB2C and TB1O with external electrical devices will be described in more detail hereinafter. In the embodiment of the invention shown here the main controller 12 operates in conjunction with the option board 22 and if desired controls the three circuit breakers MAIN 1, MAIN 2 and TIE. In this embodiment of the invention SOURCE 1 and SOURCE 2 are presumed in an unlimiting way to represent electrical utilities. However, in an alternate embodiment of the invention, SOURCE 2, for example, may be a stand-by local electrical generator (see FIG. 4) which is actuated into operation by the main controller 12. LOAD 1 and LOAD 2 may be energized exclusively from SOURCE 1 by closing circuit breaker MAIN 1 and circuit breaker TIE and opening circuit breaker MAIN 2. Alternately, LOAD 1 and LOAD 2 may be energized exclusively from SOURCE 2 by closing circuit breakers MAIN 2 and TIE and opening circuit breaker MAIN 1. Also, circuit breaker MAIN 1 may be closed energizing LD1 exclusively from SOURCE 1 and circuit breaker MAIN 2 may be closed energizing LD2 exclusively from SOURCE 2. In the latter situation, the circuit breaker TIE remains open. In still another arrangement all of the circuit breakers MAIN 1, MAIN 2 and TIE may be closed. The LOADS LD1 and LD2 are then energized concurrently from both SOURCE 1 and SOURCE 2. For purposes of simplicity of illustration presume that SOURCE 1 is the main supply of power for LD1 and LD2. In this case the circuit breaker MAIN 1 will be closed and the circuit breaker TIE will be closed and the circuit breaker MAIN 2 will be open to be closed at a later time in the event that it is necessary to transfer the derivative of power from SOURCE 1 to SOURCE 2. SOURCE 2 in this embodiment of the invention is presumed to be a stand-by source of electrical power. The electrical energy for the main controller 12 and the option board 22 may be derived from SOURCE 1 or SOURCE 2. Electrical power, for example, from the A and C phase lines of SOURCE 1 may be provided by way of a transformer T1 to the input terminals 4 and 5 of the terminal board TB1C. Likewise, power from phase lines A and C of SOURCE 2 may be supplied by way of transformer T2 to the input terminals 14 and 15 of terminal board TB1C. Terminals 4 and 5 of terminal board TB1C are designated LINE CONTROL POWER SOURCE 1 and terminals 14 and 15 are designated LINE CONTROL POWER SOURCE 2. This power is internally handled by the main controller 12 in a manner to be described hereinafter. Externally, a portion of this power is supplied by way of terminals 7 and 12 of terminal board TB1C as the AC-LINE and NEUTRAL AC field power for the various external elements interconnected with main controller 12 or the option board 22. In one embodiment of the invention the electrical power derived from SOURCE 1 and SOURCE 2 as well as the field power is 120 volt alternating current. Terminal 6 on terminal board TB2C is entitled MAIN 2 REPORT BACK and terminal 5 thereof is entitled MAIN 1 REPORT BACK. Both of these are externally fed from auxiliary contacts 28 and 30 on the circuit breakers MAIN 2 and MAIN 1, respectively. Auxiliary contacts 28 and 30 control power from the AC-LINE field wiring lead. When the circuit breaker MAIN 2 is closed, normally open contact 28 is closed, this puts AC voltage on terminal 6 of terminal board TB2C. When the circuit breaker MAIN 1 is closed, auxiliary contact 30 is closed, providing AC voltage on terminal 5 of terminal board TB2C. If contacts 28 and 30 are open circuit breakers MAIN 1 and MAIN 2 are open. If contacts 28 and 30 closed, circuit breakers MAIN 1 and MAIN 2 are closed. It is possible to have circuit breakers MAIN 1 and MAIN 2 both opened, both closed or in different states. Terminals 7, 8 and 9 of terminal board TB2C are externally connected to the OFF, AUTO, and MANUAL output terminals of the mode selector switch 14 as described previously with respect to FIG. 2. Correspondingly, the input terminals 7, 8 and 9 of terminal board TB2C are identified as OFF, AUTO and MANUAL, respectively. When the switch 14 is in the OFF state, controller 12 does not operate to control the circuit breakers MAIN 1, MAIN 2 or TIE. If on the other hand, the switch 14 is in the MANUAL state, then the control 12 may be manually manipulated to place the circuit breakers MAIN 1, MAIN 2 and TIE in various states of conduction or non-conduction. Finally, if the switch 14 is in the AUTO mode, then controller 12 will operate to automatically cause the circuit breakers MAIN 1, MAIN 2 and TIE to open or close in appropriate circumstances in accordance with a predetermined set of conditions which are programmed into the controller 12 in a manner to be described hereinafter. Input terminals 10 and 11 of terminal board TB2C are entitled AUXILIARY TRANSFER 1-2 and AUXILIARY TRANSFER 2-1, respectively. These terminals are connected to pushbutton switches 32 and 34, respectively, the other ends of which are connected to the AC-LINE lead. When the switch 14 is in the MANUAL mode, then actuation of pushbutton 32 will cause a transfer of power from SOURCE 1 to SOURCE 2 by appropriate operation of circuit breakers MAIN 1, MAIN 2 and/or TIE. On the other hand, if the operator depresses pushbutton 34 the controller will cause transfer of power from SOURCE 2 to SOURCE 1 by corresponding operation of the circuit breakers MAIN 1, MAIN 2 and/or TIE. Terminal 14 of terminal board TB2C is designated GF LOCK-OUT and it is connected to contact device designated GFI which may be part of a separate ground fault sensing system. The contact GFI is powered by the AC-LINE lead. Terminal 12 of terminal board TB2C is connected by way of a pushbutton 36 to the AC-LINE lead. Terminal 12 is designated as LOCK-OUT RESET. In the event that a ground fault lock-out has occurred by actuation of the GFI relay the controller 12 will prevent closure of all circuit breakers MAIN 1, MAIN 2 and TIE. In order to return to normal operation, pushbutton 36 is actuated which in turn will reset the circuit breakers MAIN 1, MAIN 2 and/or TIE if they tripped regardless of what status the mode selector switch 14 is in and provided that the ground fault has cleared. Terminals 13 and 15 of terminal board TB2C are designated GENERATOR STOP and GENERATOR START, respectively. As is best described with respect to the embodiment of FIG. 4 to be described hereinafter they internally cooperate with output terminals 1 and 2 of terminal board TB1C which are collectively designated GENERATOR OUTPUT START. An auxiliary generator starting system may be externally interconnected with the terminals 1 and 2 of terminal board TB1C for starting the auxiliary generator at an appropriate time for supplying power to the system. For example, SOURCE 2 may be the auxiliary generator. The actuation of the generator will take place regardless of whether the mode selector switch 14 is in the MANUAL or AUTO mode. Terminals 10, 11 and 12 of terminal board TB1C represents the common NEUTRAL for SOURCE 1, SOURCE 2 and the output control or field power lead AC-LINE. Terminals 8 and 9 of terminal board TB1C cooperate with terminal 7 thereof to provide the aforementioned output field power. The closing coils for the circuit breaker MAIN 1 and MAIN 2 are interconnected externally to the input terminals 1 and 2 of the terminal boards TB2C. These outputs are designated respectively CLOSE 1 and CLOSE 2. Energization of terminals 1 and 2 of terminal board TB2C will actuate the closing coils CC for the circuit breakers MAIN 1 and MAIN 2 and close those circuit breakers. In a like manner, terminal 4 for terminal board TB1O of option board 22 is interconnected with the closing coil of the TIE breaker. External energization of terminal 4 of terminal board TB1O will cause the TIE circuit breaker to close. Terminals 1, 2 and 3 respectively of terminal board TB1O of the option board 22 are output terminals which are interconnected respectively with the trip coils TRIP 1, TRIP 2 and TRIP TIE of the circuit breakers MAIN 1, MAIN 2 and TIE, respectively so that energization of any of those terminals will cause the associated circuit breaker to trip or open. The neutral for the option board 22 is supplied by way of terminal 7 of terminal board TB1O. Terminals 10, 9 and 12 of terminal board TB1O of option board 22 are designated MAIN 1 TRIP, MAIN 2 TRIP and TIE TRIP, respectively. Each of these terminals is an input terminal which is interconnected with a pushbutton 40, 42 and 44, respectively for external manual control of the tripping of the circuit breakers MAIN 1, MAIN 2 or TIE, respectively by way of terminals 1, 2 and 3 of TB1Q. In a like manner, terminals 11, 14 and 13 of the terminal board TB1O represent the CLOSE inputs for the circuit breakers MAIN 1, MAIN 2 and TIE, respectively. These terminals are externally connected to pushbuttons 46, 48 and 50, respectively for manual closing of the circuit breakers MAIN 1, MAIN 2 and TIE, respectively by way of terminals 1, 2 and 4 respectively of TB1Q. Terminal 15 of terminal board TB1O is the TIE BREAKER REPORT BACK input terminal which is connected to a normally open auxiliary contact 52 on the TIE breaker. As will be described later hereinafter the front panel terminal board J8 is interconnected with the front panel 16 by way of a lead 54 as is best shown in FIGS. 5G and 6B.

Referring now to FIG. 4 a schematic block diagram of another embodiment of the invention is shown. In this case no option board is utilized. All of the elements shown in FIG. 4 are identical to those with similar reference symbols in FIG. 3. In this case SOURCE 2 may be considered to be an auxiliary generator G. There may be provided a transfer motor TM which is interconnected by way of relay contacts with terminals 1 and 2 on terminal board TB2C. Furthermore there is interconnected with the terminals 1 and 2 of terminal board TB1C a starting circuit 62 for the generator G. This will be described hereinafter with respect to the embodiment of FIG. 4. Also, interconnected with terminal 15 of terminal board TB2C is a start pushbutton 58 for the generator start circuit 52. There is connected with terminal 13 of terminal board TB2C a stop pushbutton 60. Manual actuation of the start pushbutton 58 will cause the internally connected GENERATOR START OUTPUT contact to close, thus energizing the start circuit 62 of the generator G thus bringing that generator G into a disposition of providing electrical power at phase lines A, B and C on the right of FIG. 4. On the other hand, actuation of the pushbutton 60 will stop the generator G in a similar manner. The generator G may be started either manually as previously described or automatically in a manner to be described hereinafter. Generator G may also be periodically exercised by the system. In a like manner, once the generator G has been placed in a disposition of providing electrical power at SOURCE 2 the transfer motor TM may be actuated to open MAIN 1 and close MAIN 2 so that the load LD1 may be empowered from the generator G. Subsequent energization of terminals 1 and 2 of terminal board TB2C in a manner to be described hereinafter may cause the transfer motor TM to cause circuit breaker MAIN 2 to open and cause circuit breaker MAIN 1 to close thus reenergizing load LD1 from SOURCE 1. The transfer motor arrangement may also be used with the embodiment of FIG. 3 in place of the closing coils MAIN 1 and MAIN 2. Correspondingly the closing coils may be used instead of the transfer motor for the embodiment of FIG. 4.

Referring now to FIGS. 3 and 5A there is shown the power supply auctioneering circuit associated with terminals 4, 5, 7 through 12, 14 and 15 of terminal board TB1C. Single phase 120 volt alternating current may be supplied to terminals 4 and 5 by way of transformer T1. From there it is passed through a filter Fl to one pole of a switch SW1. In a like manner single phase 120 volt AC power is provided to terminals TB1C 14 and 15 from SOURCE 2. This power is provided by way of another line to another pole on the switch SW1. The switch SW1 is controlled by a field effect transistor FET1 and a control signal designated CONTROL-PW. This latter signal is provided by another portion of the controller in a manner to be described hereinafter. Depending upon the status of the signal CONTROL-PW, the single phase voltage from SOURCE 1 or SOURCE 2 will be auctioneered to be provided to the terminals 7, 8 and 9 on terminal board TB1C for the line voltage AC-LINE. There also being provided NEUTRAL at terminals 10, 11 and 12 of terminal board TB1C. The 120 volt AC signal is additionally supplied to a transformer T3 and from thence to a full wave bridge rectifier BG1. The output voltage V+UNREG of the full wave bridge rectifier BG1 is provided to a filter capacitor F2. The circuit which includes the filter Fl, the transformer T3 and the bridge rectifier BG1 is identified as source module SM1. A similar source module SM2 provides power to the output of the common filter F2 so that the voltage V+UNREG may come from either SM1 or SM2 depending upon which one of either or both sources are utilized at the time. The input circuit for the controller 12 associated with terminals 1 through 4 of connector J5 and terminals 1 through 4 of connector J6 is also described. Each of the phase lines A, B and C and the neutral for SOURCE 1 is supplied respectively to terminals 1 through 4 of connector J5 and each of the phase voltages A, B and C and the neutral for SOURCE 2 is supplied to respectively terminals 1 through 4 of connector J6. Each of the aforementioned phase voltage terminals is internally connected to separate signal conditioning modules SC1 through SC6 respectively. The neutrals are interconnected to the neutral of each module. All of the signal conditioning modules SC1 through SC6 may in one embodiment of the invention be the same. In each case, the voltage is supplied to a resistor and transformer T4 and thence to a filter network F3 comprising two capacitors and one resistor connected in .pi. configuration. The transformer T4 in cooperation with the resistor act to convert the phase voltage to a relatively low level corresponding current. Each of the current signals from the signal conditioning modules SC1, SC2 and SC3 is provided concurrently to the X, Y and Z inputs of an analog multiplexer MX1. Multiplexer MX1 is empowered on terminal 16 thereof by the voltage V2 which in one embodiment of the invention may be a highly filtered 5 volt signal. The INH input terminal of the multiplexer MX1 is grounded through a resistive element for testing purposes and the VSS and VEE input terminals of the multiplexer MX1 are grounded. The X1, Y1 and Z1 output terminals of the multiplexer MX1 are connected together and to the