Neutral bonding system for uninteruptible power supply

A UPS device of universal application provides a pair of backfeed relays, which are mandated by certain countries outside the United States, controlled by an overall control circuit to perform in conjunction with the connection of neutral to system ground to avoid damage to a load, UPS and power utility. The control circuit is responsive to an anomaly in the power supply of a power utility to enter a backup mode wherein power is supplied by a battery power supply through an inverter to the load. Entry into backup mode occurs with a delay-based switching logic which governs the control circuit's operation of the backfeed relays and formation of the neutral to system ground connection.

CROSS-REFERENCE TO RELATED APPLICATIONS 
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
Not applicable. 
BACKGROUND OF THE INVENTION 
The rise in complexity and sophistication of electronically controlled 
devices and systems has been observed to generate a concomitant need for 
higher quality and very stable sources of power. This need particularly 
has been witnessed in connection with computer systems, including modems, 
printers and copiers. 
Directly supplied utility power alone is found to be unacceptable for such 
equipment as a consequence of line power anomalies now typically 
encountered. These anomalies are manifested as any of a variety of 
phenomena. For example, out of specification voltages, referred to as 
"sags," are represented as a reduction in rms voltage values over a half 
cycle interval or more. Where such voltage reductions persist within 
important grids, they are conventionally referred to as "brown outs." 
In addition to "sags" as above described, over-voltage excursions referred 
to as "surges" may be encountered which, in general, are manifested as 
deviations above nominal rms value lasting for more than half a cycle. 
These surges generally are encountered in conjunction with load dropping 
activities. 
Subcycle abnormalities also are witnessed in the line power supplies. For 
example, high voltage, short-term spikes may occur. Such excursions have 
been observed to be caused, inter alia, by lightening strikes or 
sub-station or capacitor switching by a utility. 
Static noise conditions also may be encountered in the line power supplies. 
Such noise phenomena will include common mode noise occasioned by the 
operation of electrical equipment in close proximity to the source being 
relied upon or through load switching. Further, transverse mode noise also 
may be encountered appearing line-to-line and having similar causation. 
When encountered within a computer environment, the above cataloged 
anomalies in line power will have a variety of effects. Line noise may 
result in data error, unprogrammed jumps and software/data file 
alterations. Momentary under- and over-voltage generally results in 
automatic computer power down. 
Efforts to overcome the anomalies of line power supplies have evolved a 
variety of power conditioning devices. One such device is the 
uninterruptible power supply (UPS). A UPS system consists of a battery 
power supply, an inverter, a number of switches and a control circuit. A 
number of different types of UPS systems have been devised including 
on-line, off-line and interactive UPS systems. 
The input to a single phase UPS system consists of three conductors, line, 
neutral and safety ground, which connect to the corresponding three lines 
of a power utility. The output of a UPS system consists of line, neutral 
and safety ground conductors which are connected to the load. A control 
circuit monitors the three line power supply sensing any anomalies in 
voltage supplied by the utility during the time when the UPS system is in 
standby mode. In the event of such an anomaly, the control circuit derives 
a control input which opens the switches which connect the UPS system to 
the line power supply of the power utility. The UPS system then is 
disconnected from the line power supply, and the UPS system operates in a 
backup mode. In backup mode, power then is delivered from the battery 
power supply through an inverter to the load. Backfeed protection switches 
are opened and the battery power supply is engaged in such a way as to 
provide a continuous supply of power to the load. 
Because of the widespread growth of technology and increasing 
globalization, the market for UPS systems is worldwide. In designing UPS 
systems, manufacturers must be aware of and comply with the regulations 
regarding such systems in each of the countries in which it plans to 
market a system. Approximately eighteen countries in Europe have joined 
together to form the European Committee for Electrotechnical 
Standardization (CENELEC). Subject to certain conditions, each European 
Standard promulgated by the CENELEC must be given the status of a national 
standard without any alteration. A European Standard may be amended by the 
CENELEC and each exists in the three official versions, English, French 
and German. Participating countries include Austria, France, Germany, 
Italy, Spain and the United Kingdom among others. 
While the United States is not a member of the CENELEC and thus not subject 
to its regulations, manufacturers in this country typically comply with 
the regulations promulgated by the Underwriter's Laboratory. The relevant 
UL standards governing UPS systems are UL 1778 and UL 1950. Similarly, 
other countries, such as Australia and the far East, which are not members 
of the CENELEC have promulgated their own national standards. 
While there may be some similarities among some countries as to some 
requirements, regulation throughout the world lacks uniformity. Lack of 
uniformity led to the formation of the CENELEC, but the European Standards 
have only alleviated the problem to a small degree. Among the CENELEC and 
other nations, the differences among the varying regulations are 
substantive not merely formalistic. Several differences between the 
European and American standards are illustrative. In the United States, 
the National Electric Code (NEC) requires that safety and neutral lines be 
tied to ground at an entry box or panel before the power supply from the 
utility enters a building. There is no European Standard which requires 
such grounding. Another example is the number of conductors required to 
open when a non-separately derived UPS system operates in backup mode. The 
United States requires only the singular opening of the line conductor, 
while in Europe, two switching relays are required to open both the line 
and neutral conductors. EN 50091-1-1. 
In countries where the neutral and safety lines are not required to be tied 
to ground at the box or panel, as they are in the United States, a problem 
has been encountered involving "creeping voltage." UPS systems are 
generally connected to a load, such as a computer, with EMI capacitors 
which are used to reduce emissions and radio-frequency interference. These 
capacitors are connected between the line and neutral conductors, between 
the line and safety conductors and between the neutral and safety 
conductors. The voltage at the neutral line should be constantly 0 Volts. 
When the UPS system operates in backup mode, the capacitors effectively 
act as a voltage divider between the active, neutral and safety 
conductors, the capacitance between the active conductor and chassie 
ground and that between neutral and chassie ground being of approximately 
equal value. Where the neutral conductor is not connected to frame or UPS 
safety ground, and thus is left floating, a voltage exists at the neutral 
conductor with respect to ground. This creeping voltage, experienced by 
the neutral conductor with respect to ground, is approximately half of the 
total voltage of the utility which for such total of 230 Volts, as in 
Europe, is 115 Volts. A voltage of that magnitude may cause damage to 
sensitive computer equipment. 
The problem of creeping voltage does not occur in the United States where 
the neutral conductor is connected to ground at the panel, effectively 
maintaining zero voltage with respect to frame ground. For other countries 
which do not require such a connection, the problem of creeping voltage 
must be addressed. One solution to the problem is a hard tie between the 
neutral and safety conductors. Such a tie is required in some countries, 
such as Australia. However, in other countries, predominantly those in 
Europe, the active and neutral lines of the line power supply may be 
switched, which occurs as much as fifty percent of the time. When the 
active and neutral lines are switched, a hard tie connects the active 
line, instead of the neutral line, to frame ground which may cause a 
short-circuit to the utility. Therefore, while a hard tie is a solution 
for UPS systems in some countries, such as Australia, in Europe a 
different solution is required. 
As the above indicates, maintaining a zero voltage at the neutral line may 
not be a problem at all in one country, a problem with a simple solution 
in another and a problem with an as yet undiscovered solution in another. 
Currently, manufacturers of UPS systems have been forced to develop, 
supply and provide support for a number of different systems which address 
this voltage problem but remain in compliance with differing regulatory 
standards and line setups. 
BRIEF SUMMARY OF THE INVENTION 
The present invention is addressed to an uninteruptible power supply having 
universal application throughout the world, particularly in Asian, 
European and South American countries, regardless of differing national 
electrical standards and regulations. Customization of a number of UPS 
systems to meet differing regulations involves considerable expense. A 
universal design topology makes such country-by-country customization 
unnecessary, and, in addition, eliminates expenses associated with 
identification and tracking which are needed to ensure delivery of UPS 
systems with proper specifications to each country. Further, excess demand 
in one country may be met with excess supply from another with no 
modification of the UPS required, saving both time and money. A common UPS 
design, thus, provides decreased costs in production and warehousing and 
increased convenience in meeting demand. 
A pair of backfeed relays, which are mandated by countries outside the 
United States, are controlled by an overall control circuit to perform in 
conjunction with the connection of neutral to system ground to avoid 
damage to the load, UPS and power utility. The control circuit is 
responsive to an anomaly in the power supply of a power utility to enter a 
backup mode wherein power is supplied by a battery power supply through an 
inverter to the load. Entry into backup mode occurs subsequent to a series 
of delay intervals which govern the control circuit's operation of the 
backfeed relays and formation of the neutral to system ground connection. 
One aspect of the invention is the inclusion of a unique neutral bonding 
circuit to form the neutral to system ground connection. The neutral 
bonding circuit is included within the UPS, but is an optional feature 
that must be enabled by the user to be operational. The neutral bonding 
circuit provides system protection by automatically coupling the neutral 
line to safety ground when the UPS enters backup mode. Coupling of neutral 
to safety ground is required in some countries, such as Australia, and 
also eliminates voltage buildup, i.e. "creeping voltage." The automatic 
coupling is provided by the neutral bonding circuit in the form of a 
neutral bonding relay which is maintained in a normally open 
configuration. When the overall control circuit senses an anomaly in 
utility power, the neutral bonding relay is closed under a protective 
timing feature providing electrical coupling of neutral to system ground. 
This electrical coupling maintains the neutral line at substantially zero 
volts while the UPS operates in backup mode. When the anomaly terminates, 
the neutral bonding relay is opened and maintained in an open 
configuration until the UPS again enters backup mode. Thus, coupling of 
neutral to system ground is automatically provided and removed when the 
UPS enters backup mode and returns to standby mode. In countries where 
this coupling is not required or desired, the neutral bonding circuit is 
simply not enabled by the user. 
The neutral bonding circuit also is designed to accommodate differing power 
utility inputs which occur from country to country, including the reversal 
of line and neutral. A protective timing feature prevents the automatic 
coupling of neutral to system ground by the control circuit until the UPS 
is disconnected from the power supply of the power utility. A series of 
delay intervals, created by logic or a microprocessor, ensure that the 
backfeed protection relays open before the neutral bonding relay closes 
when the UPS transitions to backup mode. Similarly, the series of delay 
intervals also ensure that the backfeed protection relays close after the 
neutral bonding relay opens when the UPS returns to standby mode. Thus, 
the delay intervals time the opening and closing of the relays such that 
an unanticipated coupling of any of the inputs to system ground will not 
occur. 
Another aspect of the invention provides for the inclusion of an enabling 
assembly incorporating a user actuable screw. The presence of the screw on 
the rear face of the UPS alerts the user that some action must be taken 
regarding the operation of the UPS. Engagement of the screw enables the 
neutral bonding circuit. The screw is accessible through an opening on the 
front face of the UPS device and can be engaged with a screwdriver. The 
position of the screw within the opening allows the user to determine at a 
glance whether the neutral bonding circuit is enabled. 
Other objects of the invention will, in part, be obvious and will, in part, 
appear hereinafter. The invention, accordingly, comprises the apparatus 
possessing the construction, combination of elements, and arrangement of 
parts which are exemplified in the following description. 
For a fuller understanding of the nature and objects of the invention, 
reference should be had to the following detailed description taken in 
connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a typical UPS device configured for sale outside the 
United States, particularly in Asian, European and South American markets, 
employing the features of the invention is represented generally at 10. 
UPS 10 includes a housing 12, the rearward face of which is shown at 14. 
Rearward face 14 includes an input receptacle 16 which connects the UPS 10 
to the power supply of a power utility. Conductors 18, 20 and 22 at input 
receptacle 16 connect the line, neutral and safety ground conductors of 
the UPS 10 to the corresponding three lines of the power utility. Rearward 
face 14 also includes output receptacles 24-30. Output receptacles 24-30 
connect the UPS system to the loads for which power from the utility is to 
be supplied. UPS 10 is designed for relatively smaller loads, for example, 
up to 3 KVA. Because the device 10 is intended for use outside the United 
States, output receptacles 24-30 are provided as European style plugs. A 
communication interface 32 is incorporated within device 10 to allow the 
user to connect option cards for additional communication options. A 
communication port also is present at 34 allowing connection of the UPS 10 
to a computer. An output voltage selector switch 36 is provided adjacent 
port 34. Using output voltage selector 36, the user can select different 
output voltages. A cooling fan (not shown) is included within housing 12 
to prevent the overheating of components contained therein. The exhaust 
grid of the cooling fan is shown at 38. An input fuse is provided at 40 
for internal protection. 
An enabling assembly forming a component of a neutral bonding circuit of 
the invention is shown generally at 42. Contained within housing 12, 
enabling assembly 42 is attached to the interior surface of rearward face 
14 by screws 44 and 46. Enabling assembly 42 includes an electrically 
conductive circuit completing threaded component shown at 48. The 
component 48, for example, may be implemented as an electrically 
conductive machine screw. Screw 48 is installed through and may be 
accessed by the user through aperture 50 and is manually actuable by a 
screwdriver to complete the noted neutral bonding circuit (not shown). 
Under the United States Electrical Code, neutral and safety ground lines 
are tied to ground at the entry box or panel of a building facility before 
the power supply from a power utility is permitted to enter. This 
permanent connection maintains the neutral line at substantially zero 
voltage. Outside the United States, other countries' national electrical 
regulations and standards typically do not require such a connection. 
Where this connection is not made, when a UPS device operates in backup 
(battery powered) mode, voltage at the neutral conductor within the UPS 
apparatus is left floating. If the neutral conductor so floats, the system 
may experience backup voltage, i.e. "creeping voltage," from the neutral 
conductor to frame ground. This backup voltage may damage the UPS device 
or load. 
FIG. 2 represents components of interest of a typical UPS circuit of the 
prior art where there is no connection of the neutral conductor with 
system ground. The UPS components of FIG. 2 include two backfeed 
protection relays connected into the line and neutral conductors, two such 
switching devices typically being mandated by countries outside the United 
States. These backfeed protection relays are represented respectively as 
switches at 68 and 70. In the United States, only one relay, controlling 
line input, is required to disconnect the power supply from the power 
utility. The three lines of a power utility are connected to corresponding 
line, neutral and safety ground conductors of the UPS device which are 
shown at 62, 64 and 66 respectively. Safety ground conductor 66 is coupled 
to chassis or frame ground at 67. When operating in standby mode, i.e. 
under utility power, backfeed protection relay switches 68 and 70 are 
actively retained in a closed circuit configuration so as to supply 
utility power to a load. However, upon entry into a backup mode, switches 
68 and 70 are opened, as shown, to disconnect line conductor 62 and 
neutral conductor 64 from the corresponding utility lines. Power then is 
supplied by a battery power supply (not shown) through an inverter to the 
load. The inverter is shown as a symbol 72. EMI filter capacitors as 
depicted at 74, 76 and 78 are conventionally included within typical UPS 
systems, as well as electronic loads, and are associated with the line, 
neutral and safety (frame) ground conductors 62, 64 and 66 as symbolically 
represented. In this regard, a capacitance represented by capacitor symbol 
74 is connected between neutral conductor 64 and safety or frame ground 
conductor 66. Similarly, a capacitance represented by capacitor symbol 76 
is connected between line conductor 62 and safety or frame ground 
conductor 66, while a capacitance represented by capacitor symbol 78 will 
be present between line conductor 62 and neutral conductor 64. 
Capacitances represented by capacitor symbols 74 and 78 usually are 
balanced or of approximately equal value. In conventional fashion, EMI 
capacitor functions 74, 76 and 78 act as filters to reduce emission and 
radio-frequency interference. 
Safety ground conductor 66 is associated with the safety ground line of the 
power utility. Conductor 66, in effect, extends through the UPS to the 
output of the system. 
EMI capacitors as represented by symbols 74, 76 and 78 effectively create 
the equivalent circuit shown in FIG. 3. Looking to that figure, inverter 
72 is shown connected between line conductor 62 and neutral conductor 64. 
This equivalent circuit demonstrates that capacitances, represented by 
capacitor symbols as at 80 and 82, are present between line conductor 62 
and chassis ground 67, as well as between neutral conductor 64 and such 
ground. Additionally, they are of approximately equal value of 
capacitance. Ideally, neutral conductor 64 should be maintained at 0 volts 
with respect to chassis ground, but equivalent capacitances 80 and 82 will 
react somewhat as an a.c. voltage divider which creates a voltage along 
neutral conductor 64 with respect to chassis ground. For example, in 
backup mode the a.c. power supply provided by inverter 72 creates a 
voltage, V.sub.0, between line conductor 62 and neutral conductor 64 as at 
86. Because of the presence of equivalent capacitors 80 and 82, half of 
V.sub.0 at 88 is produced between line conductor 62 and chassis ground 67. 
Half of voltage V.sub.0 at 90 (1/2 V.sub.0) also is seen between neutral 
conductor 64 and chassis ground. In such a UPS system where the output 
voltage is, for example, 230 volts, the neutral to ground voltage will be 
approximately 115 volts. A presence of such voltage may cause damage to 
the UPS or any load connected to the UPS. 
FIG. 4 represents certain components of a UPS circuit of the prior art with 
neutral conductor 64 permanently connected to safety ground conductor 66 
as represented at line 92. Such a connection prevents the build-up voltage 
problem described above and is required in some countries, such as 
Australia. This type of permanent tie is problematic in European, and 
perhaps other countries, where, as often as 50% of the time, line and 
neutral from the power utility are switched. FIG. 5 represents the circuit 
of the UPS device of FIG. 4 whose internal conductors are connected to the 
power supply of a power utility in a manner where line and neutral inputs 
are inadvertently switched. The neutral conductor remains identified at 
64, the line conductor at 62, with the safety ground conductor remaining 
at 66. With line and neutral utility inputs switched, permanent tie 92 now 
connects line conductor 62 with safety ground conductor 66. A tie between 
these two conductors creates a current loop 94 which can cause a short 
circuit and damage. 
FIG. 6 represents one approach taken to deal with the problem of voltage 
development at frame ground-to-neutral where a permanent tie, as described 
at 92 in connection with FIGS. 4 and 5, is sought to be avoided. The 
circuit is configured, as in FIG. 2, with line conductor 62, neutral 
conductor 64 and safety ground conductor 66. Backfeed protection relay 
switches 68 and 70, inverter 72, and capacitor symbols 74, 76 and 78 
reappear as configured in FIG. 2. In this approach, an added Capacitor 76 
is provided. At first observance, the circuit of FIG. 3 would be modified 
by the arrangement of FIG. 6. In this regard, because capacitor 76 is 
disconnected from the output during backup mode, instead of acting as an 
a.c. voltage divider, splitting voltage between neutral conductor 64 and 
line conductor 62, the large capacitance of capacitor 76 is intended to 
reduce the voltage between neutral conductor 64 and chassis or frame 
ground 67 so as to approach 0 volts. This approach, while effective for 
resistive loads, is not effective for electronic loads, i.e. computers, 
which have self-incorporated EMI filter capacitors. In this regard, those 
electronic load carried capacitors bring the capacitive balance described 
in FIG. 3 back into the system to create the unwanted neutral to ground 
voltage buildup. 
Referring to FIG. 7, a block diagrammatic representation of certain 
circuitry employed with a typical UPS device, including the neutral 
bonding and enablement features of the invention, is provided. Certain 
numeration from FIGS. 1 and 2 is retained in FIG. 7. Line and neutral from 
the power utility are shown at lines 106 and 108 entering the UPS device 
10 at the input represented at block 16. Line and neutral are now 
conductors within the UPS device 10 and are represented respectively at 
lines 112 and 114. These then reflect the attributes of the incoming 
utility lines. Line 110 connects at input 16 to become frame or chassis 
ground 113. From input 16, conductors 112 and 114 extend to backfeed 
protection switches represented at block 116. Block 116 represents a pair 
of backfeed protection relay switches which are controlled as represented 
by line 142 from an Inverter/Switching/UPS Control represented, inter 
alia, at block 122. UPS Control 122 responds to anomalies in the power 
supply of the power utility to enter a backup mode wherein power is 
supplied to the load from a battery power supply. Anomalies may result 
from out of specification voltages, such as "sags" or "surges," power loss 
or from various noise phenomena. When an anomaly is not sensed, the UPS 
control 122 operates the UPS in standby mode. UPS Control 122 actively 
maintains backfeed protection switches 116 in a closed configuration, and 
utility power is transmitted via lines 118 and 120, thence via lines 124 
and 126 to an Output Control Switching function as represented at block 
128. UPS Control 122 controls the Output Control Switching 128 via line 
130. Output Control Switching function 128 is present as a conventional 
UPS switching function which allows power to be supplied to output lines 
132, 134 and 136 which are connected, in turn, to the corresponding line, 
neutral and safety ground connectors of a load (not shown). Load line 136 
connects to chassis or frame ground 113. 
As noted above, UPS Control 122 monitors the power supply from the power 
utility via sensing lines 138 and 140. When an anomaly is sensed, the 
Control function 122 derives a control input condition as well as a 
neutral bonding input and enters a backup mode. The control input 
condition is presented via line 142 to render the backfeed protection 
switches of function 116 in an open circuit condition. Utility power is no 
longer supplied to the load. Instead, power is supplied, in conventional 
fashion, via lines 144 and 146 from the battery power supply represented 
at block 148. This battery-originated power supply passes to and is 
treated by the inverter of UPS Control 122 to output switching 128 via 
lines 124 and 126. Output Control Switching continues to function, under 
the control of UPS Control 122 to connect the power supply to the output 
lines 132, 134 and 136 which connect to or represent the load. 
A Neutral Bonding Switch Assembly represented at block 150 is connected to 
neutral conductor line 126 via line 152. Switch assembly 150 may be 
enabled by the user by virtue of a Neutral Bonding Enable Assembly now 
represented by block 42 via line 154. (see additionally FIG. 1) When 
enablement is carried out by the user at function 42, the UPS Control 122 
will be capable of deriving a neutral bonding input condition by 
transmission of a signal via line 156 to switch assembly 150. This occurs 
when the control function 122 senses an anomaly in the power supply of the 
power utility via sensing lines 138 and 140. When the input condition is 
asserted via line 156, switch assembly 150 provides electrical coupling of 
line 126 to chassis or system ground 113 through Neutral Bonding Enable 
Assembly 42. A protective timing feature ensures that such electrical 
coupling of line 126 to frame ground will not be provided until UPS 10 is 
disconnected from the power utility at switch function 116. 
When the anomaly terminates, the UPS control 122 senses such return to 
normalcy and removes the neutral bonding input condition by removal of the 
signal or input condition at line 156 to open the switch of switch 
assembly 150 and thus disconnect line 126 from chassis or frame ground 
113. UPS Control 122 also removes the control input condition at line 142 
to cause closure of the backfeed protection switches at 116. As part of 
this procedure, Switching Control at function 122 then transitions the UPS 
10 from backup mode to standby mode, effectively isolating the battery 
power supply from the inverter function. Power from the utility then is 
supplied to the output lines 132, 134 and 136 in standby mode, as 
described above. Typically, the batteries are re-charged during the 
ensuing standby mode. The protective timing feature, described above, also 
ensures that the neutral bonding electrical coupling will be terminated 
before power is supplied from the power utility to return to a standby 
mode. 
Looking to FIG. 8, interior components of enabling assembly 42 are shown. 
Numeration from FIG. 1 is retained where appropriate in FIG. 8. A bracket 
160 is attached to rearward side of face 14 with machine screws 44 and 46. 
Connected to the interior of bracket 160 is a printed circuit board 162 
upon which two conductive printed circuit pads at surfaces 164 and 166 are 
formed. Also connected through bracket 160 is the earlier described 
enabling screw 48 which is manually insertable through aperture 50 to 
effect mutual physical electrical engagement and create circuit completion 
between printed circuit pads 164 and 166. Electrical engagement of circuit 
pads 164 and 166 enables a neutral bonding circuit, as at 150 (FIG. 7), 
which provides electrical coupling of the neutral conductor to ground when 
the UPS 10 operates in backup mode. At the outset of use of UPS device 10, 
the presence of such an aperture 50 and the presence of a screw 48 serves 
to alert the user that a decision must be made regarding the invocation of 
a neutral bonding option. By simply inserting the screw 48, the neutral 
bonding circuit may be enabled by the user with a screwdriver without 
disassembly procedure. 
FIG. 9 shows a side view of the assembly 42 of FIG. 8 with components 
removed to show internal features. Bracket 160 is shown with openings 170 
and 172 into which machine screws 44 and 46 are engaged to attach bracket 
160 to the rearward surface of rearward face 14 of UPS 10. Bracket 160 
supports printed circuit 162 which is attached thereto by bolt and nut 
assembly 174. The bolt assembly 174 also provides electrical connection of 
printed circuit pad 164 to frame ground. Conductive pad 166 of printed 
circuit board 162 is coupled to a lead 176 which provides connection with 
the neutral line of the power utility. Screw 48 is manually threadably 
engaged within threaded opening 178 in bracket 160. The screw 48 provides 
circuit completing electrical engagement between printed circuit pads 164 
and 166 as shown by the phantom representation of its head component. 
FIG. 10 is a block diagrammatic representation of the circuitry employed 
with the invention which shows in greater detail the operation of the UPS 
Control Circuit of FIG. 7. FIG. 10 also demonstrates the protective timing 
features associated with the backfeed protection and neutral bonding 
switches. The numeration of FIG. 7 is retained where appropriate in FIG. 
10. Internal line and neutral conductors 112 and 114 extend to the 
Inverter and Switching function of the UPS system represented at block 
182. Battery power supply 148 is connected by lines 144 and 146 to the 
Inverter and Switching function at block 182. Output lines 132 and 134, 
which are, in effect, a continuum of line and neutral conductors 112 and 
114, extend from Inverter and Switching function at block 182 to supply 
either utility or battery backed-up power to a load. Communication between 
the UPS Control Circuit represented at block 184 and the Inverter and 
Switching function at block 182 is shown via dual-directional arrow 186. 
Control Circuit 184 communicates with the remaining UPS functional blocks 
of FIG. 7 as represented at line 190. When UPS Control Circuit 184 
maintains UPS device 10 in standby mode, it presents a logic high signal 
at line 188. In backup mode, a low logic signal occurs at line 188. The 
signal condition at line 188, inter alia, controls the backfeed protection 
switches 116 from line 142. (FIG. 7) Because of the presence of inverting 
circuit component 196, the same signal condition at line 188 may also 
control neutral bonding switch assembly 42 from line 156. 
A series of delay functions, shown at 192, 194, 198 and 200, provide system 
protection when Control Circuit 184 transitions UPS device 10 from standby 
mode to backup mode and from backup mode to standby mode. Looking 
additionally to FIG. 11, a status table illustrates the dual states of UPS 
device 10, the corresponding conditions of the backfeed circuit and the 
neutral bonding circuit when in such states, and the corresponding delays 
associated with the circuits in the course of operational mode changes. As 
seen in FIG. 11, the delay networks are only associated with the mode 
transitions of UPS device 10 as opposed to its steady states. Returning to 
FIG. 10, in the absence of an anomaly in the power supply of the power 
utility, UPS device 10 operates in standby mode, where the backfeed relay 
switch control circuit is activated with backfeed protection switches 116 
actively retained in a closed circuit configuration. Conversely, during 
this mode the neutral bonding circuit is "off" with the Neutral Bonding 
Switch Assembly 150 being passively retained in a normally open circuit 
configuration. When it senses an anomaly in utility power at lines 138 and 
140, Control Circuit 184 transitions UPS device 10 from standby mode to 
backup mode. The signal condition at line 188 correspondingly transitions 
from a logic high state to logic low state and certain delay categorized 
intervals are carried out as represented at blocks 194 and 198. Block 194 
corresponds to Delay 2 in FIG. 11, while block 198 corresponds to Delay 3. 
Delay 2 (block 194) ensures that the backfeed circuit turns off fast in 
response to the mode switching signal condition at line 188, quickly 
opening backfeed protection switches 116 (FIG. 7). Delay 2 essentially 
approaches 0 ms.. Delay 3 (block 198) ensures that the neutral bonding 
circuit turns on following a delay, in response to the signal condition at 
line 188. The neutral bonding switch of Assembly 150 closes, for example, 
after a 10 ms. delay. This delay ensures that the backfeed protection 
switches will be opened before the neutral bonding switch is closed to 
thus avoid the short circuiting phenomena due to inadvertent line/neutral 
reversal as discussed above. 
With a logic low signal at line 188, the backfeed protection switches are 
in their normally off condition and the neutral bonding switch is actively 
retained in a closed orientation, UPS device 10 then operating in its 
backup mode. When Control Circuit 184 senses a utility return to normalcy 
at lines 138 and 140, it transitions UPS device 10 from backup mode to 
standby mode. To carry this out, Control Circuit 184 transitions the 
signal condition at line 188 from a logic low state to a logic high state, 
and delay networks 192 and 200 are employed. Block 192 corresponds to 
Delay 1 and block 200 corresponds to Delay 4 as shown in FIG. 11. Delay 4 
is relatively short, ensuring that the neutral bonding circuit turns off 
quickly in response to a change in the signal condition at line 188. Delay 
4 may effectively approach 0 ms.. Delay 1 (block 192) ensures that that 
the backfeed relay control circuit will close switches 116 following a 
delay in response to a change in the signal condition at line 188. Delay 1 
may be, for example, 10 ms.. These delays as represented at blocks 192 and 
200 ensure that the neutral bonding switch of Assembly 150 will open 
before backfeed protection switches 116 close. The UPS device 10 then 
operates in standby mode as described above. Such switch timing again 
assures that no short circuiting as described above will occur. 
The delay functions 192, 194, 198 and 200 prevent electrical coupling by 
neutral bonding assembly 150 when the UPS device 10 is receiving the line 
inputs of the power utility. Inclusion of this protective timing feature 
allows the UPS device 10 to universally accommodate differing power 
utility inputs, especially where the line and neutral are reversed. With 
the opening and closing of these switches under careful control, there can 
be no damaging connection of a power utility line input to system ground. 
Referring to FIG. 12, an electrical schematic portrayal of one 
implementation of the invention is provided with discrete electronic 
components for illustrative purposes. Certain numeration from FIG. 10 is 
retained. Line and neutral input conductors 112 and 114 are shown leading 
to paired electromagnetically actuated backfeed relay switches 208 and 
210. The inverter, which is represented at block 212, is controlled by 
Control Circuit 184, which is shown incorporating an input/output port 
214. Control Circuit 184 senses anomalies and the termination of anomalies 
in utility power as above described in connection with FIG. 7. The 
backfeed and neutral bonding control circuits described in connection with 
FIGS. 10 and 11 are represented generally at 248 and 250 respectively. 
Control Circuit 184 controls these circuits by asserting a select signal 
condition at line 188. Whether in standby mode or backup mode, power is 
supplied to a load from output at lines 132 and 134. 
Backfeed circuit 248 includes an RC network shown generally at 220 
incorporating resistor R1, capacitor C1 and diode D4 formed with line 222. 
Network 220 will exhibit a time constant of, for example 10 ms.. Line 222 
is seen directed to the base of an npn transistor Q1 which is coupled to 
ground at its emitter. The collector of transistor Q1 is coupled at line 
118 to an inductor 226 which, when energized, will close backfeed relay 
switches 208 and 210 as represented by dashed line 211. Included to 
accommodate inductive spikes is protective diode D1. Note that inductor 
226 is coupled to positive V.sub.cc. When operating in standby mode, 
application of a logic high signal will forward-bias transistor Q1 to draw 
current through inductor 226 to, in turn, retain backfeed protection 
switches 208 and 210 in closed circuit configuration. During standby mode, 
the high logic signal condition at line 188 also extends to neutral 
bonding circuit 250. Neutral bonding circuit 250 includes an RC network 
represented generally at 230 which incorporates resistor R2, capacitor C2 
and diode D2 within line 188. Network 230 will exhibit the same time 
constant as network 220, being, for example, 10 ms.. Line 188 extends to 
the base of pnp transistor Q2 whose collector is coupled to ground. The 
emitter of transistor Q2 extends at line 142 to an inductor 234 which, 
when energized, will close neutral bonding switch 238 as represented by a 
dashed line 235. Switch 238 is coupled within a line 239 which, in effect, 
is coupled between neutral conductor 132 and frame ground 113. A 
protective diode D3 is coupled across inductor 234 to accommodate 
inductive spikes. Note that inductor 234 is coupled to positive V.sub.cc. 
Neutral Bonding Circuit 250 may be enabled by an enabling assembly, such 
as that shown at 42 and as described in FIGS. 8 and 9, or by a jumper as 
shown at 252. Jumper 252 may also be a programmable electromagnetically 
actuated relay switch. A variety of enabling assemblies will occur to 
those skilled in the art. A protective fuse also is included at 240 within 
line 239. Application of a logic high signal to transistor Q2 retains it 
in an off state, no current being drawn through inductor 234 at line 142, 
and neutral bonding switch 238 is retained in its normally open 
configuration. In this regard, a high logic condition at line 188 rapidly 
charges capacitor C2 of network 230 through bypass diode D2. The resultant 
charge on capacitor C2 retains transistor Q2 in an off-state. Thus, while 
operating in standby mode, continuous application of a logic high signal 
at 188 retains the backfeed protection switches 208 and 210 in a closed 
circuit configuration and neutral bonding switch 238 in an open circuit 
configuration. 
When UPS device 10 senses an anomaly in the power supply of the power 
utility at line 190, Control Circuit 184 transitions UPS device 10 from 
standby mode to backup mode. The signal condition at line 188 
correspondingly transitions from logic high to logic low. The delay 
intervals discussed in connection with FIGS. 10 and 11 are provided by 
networks 220 and 230. Because of the presence of diode, D4, application of 
a logic low signal at line 188 will forthwith turn off transistor Q1 such 
that no current will flow through inductor 226, opening backfeed 
protection switches 208 and 210. This activity corresponds to block 194 of 
FIG. 10. When the signal condition transitions from a high state to a low 
state, Network 230 provides the longer delay discussed in connection with 
block 200 of FIG. 10. Diode D2, being reversed biased, capacitor C2 will 
discharge over a delay interval through resistor R2 to turn on transistor 
Q2. This delay interval will be, for example, 10 ms.. Transistor Q2 will 
then draw current through inductor 234 to close neutral bonding switch 
238. Neutral bonding switch 238 provides electrical coupling between 
neutral conductor 114 and system ground 113. With neutral bonding switch 
238 retained in a closed circuit configuration and backfeed protection 
switches 208 and 210 retained in an open circuit configuration, the UPS 
device 10 operates in backup mode. 
When Control Circuit 184 senses the absence of an anomaly, or the return of 
utility power to normalcy, a logic high signal will be present at line 
188. Networks 220 and 230 now provide the delays associated with blocks 
192 and 198 respectively as described in FIGS. 10 and 11. Upon transition 
from a logic low signal to a logic high signal at line 188, transistor Q2 
will be turned off forthwith due to the forward biasing of diode D2. As 
transistor Q2 turns off, no current will be drawn through inductor 234 and 
neutral bonding switch 238 revert to its normally open configuration. 
Network 220 will interpose a delay, corresponding to its time constant of, 
for example, 10 ms.. Application of a logic high signal to the base of 
transistor Q1 will again draw current through inductor 226 to close 
backfeed protection switches 208 and 210. With the neutral bonding switch 
remaining in an open circuit configuration and the backfeed protection 
switches retained in a closed circuit configuration, UPS device 10 
operates once again in standby mode. 
Referring to FIG. 13, another implementation of the invention is shown. The 
numeration of FIG. 12 is retained. Control Circuit 184 may consist of a 
microprocessor, shown at 254, which provides the delays as described in 
FIGS. 10 and 11. The presence of three inverting circuit components, 
represented at 256, 258 and 260, instead of one may be necessary to create 
a buffer where microprocessor 254 alone is unable to actuate backfeed 
protection switches 208 and 210 and neutral bonding switch 238. 
Since certain changes may be made in the above-described apparatus without 
departing from the scope of the invention herein involved, it is intended 
that all matter contained in the description thereof or shown in the 
accompanying drawings shall be interpreted as illustrative and not in a 
limiting sense.