Modular surge suppressor

An electrical switching device such as a motor starter is adapted to be controlled through control signals in control wiring and includes separable contacts; an operating mechanism for opening and closing the separable contacts; first terminals for interfacing the control signals to the operating mechanism; a modular surge suppressor circuit for suppressing a surge associated with the control signals, with the modular surge suppressor circuit including second terminals for engaging the first terminals and interfacing the control signals thereto; and a modular terminal block for interfacing the control signals in the control wiring to the modular surge suppressor circuit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a surge suppressor and, more particularly, to a 
modular surge suppressor for an electrical switching device such as a 
motor starter. 
2. Background Information 
Electrical switching devices include, for example, circuit switching 
devices and circuit interrupters such as circuit breakers, contactors, 
motor starters and motor controllers. Circuit breakers, which are 
well-known in the art, are generally used to protect electrical circuitry 
from damage due to an overcurrent condition, such as an overload fault or 
a relatively high level short circuit condition. Molded case circuit 
breakers, for example, include at least one pair of separable contacts 
which are operated either manually by way of a handle disposed on the 
outside of the case or automatically by way of an internal trip unit in 
response to an overcurrent condition. 
When the circuit breaker is on, a movable contact assembly is in contact 
with a stationary or fixed contact assembly. The closed contacts conduct a 
flow of current between a line terminal and a load terminal. When the 
circuit breaker trips or is switched off, the movable contact assembly is 
moved away from the fixed contact assembly, thus, interrupting the flow of 
current between the line and load terminals. Examples of molded case 
circuit breakers are disclosed in U.S. Pat. Nos. 4,827,369; and 4,963,846. 
Additional types of circuit interrupters include, for example, contactors, 
motor starters, motor controllers, lighting controllers, other load 
controllers and other electromechanical switching devices used for 
controlling a variety of electrical loads. Electromagnetic contactors, for 
example, include a plurality of movable electrical contacts which are 
brought into contact with a plurality of fixed electrical contacts to 
close the contactor whenever the coil is energized. On the other hand, 
whenever the coil is de-energized, the movable electrical contacts are 
separated from the fixed contacts to open the contactor. Examples of 
contactors are disclosed in U.S. Pat. Nos. 4,760,364; and 4,766,273. 
A common type of starter for loads such as motors, lighting, and the like, 
comprises an electromagnetic contactor with an overload relay. In a motor 
starter, for example, the purpose of the overload relay is to estimate the 
heat produced in the motor by line current and "trip" or stop the motor if 
the retained heat exceeds an acceptable level. The overload relay monitors 
the load current and trips the contactor open if a persistent overcurrent 
condition exists. Typically, the overload relay tracks an I.sup.2 t 
characteristic of the load current which is a measure of heating. 
Today, it is common for the overload relay to contain a microprocessor 
which digitally generates the I.sup.2 t characteristic. When the 
calculated I.sup.2 t value reaches a trip level, the contactor is tripped 
open to interrupt the flow of current to the load. 
It is known that switching the coil of a contactor may cause transients. A 
common solution to this problem is to provide a surge suppressor having 
wires for attachment of a surge suppression circuit across the contactor 
coil. However, a user must utilize a screw driver in order to connect or 
disconnect the surge suppressor to or from the contactor and, hence, there 
is room for improvement. 
SUMMARY OF THE INVENTION 
The invention is directed to an electrical switching device, adapted to be 
controlled through control signals in control wiring, with the device 
including separable contacts; a mechanism for opening and closing the 
separable contacts; a first terminal mechanism for interfacing the control 
signals to the mechanism for opening and closing the separable contacts; a 
surge suppressor circuit for suppressing a surge associated with the 
control signals, with the surge suppressor circuit including a second 
terminal mechanism for engaging the first terminal mechanism and 
interfacing the control signals thereto; and a mechanism for interfacing 
the control signals in the control wiring to the surge suppressor circuit. 
As another aspect of the invention, an electrical switching device, adapted 
to be controlled through control signals in control wiring, includes 
separable contacts; a mechanism for operating the separable contacts; a 
first terminal mechanism for interfacing the control signals to the 
mechanism for operating the separable contacts; a modular surge suppressor 
circuit at least for suppressing a surge associated with the control 
signals, with the modular surge suppressor circuit including a second 
terminal mechanism for engaging the first terminal mechanism and 
interfacing the control signals thereto, and also including a third 
terminal mechanism for interfacing the control signals to the second 
terminal mechanism; and a modular terminal block mechanism for engaging 
the control wiring and interfacing the control signals to the third 
terminal mechanism. 
As a further aspect of the invention, a motor starter, which is adapted to 
be controlled through control signals in control wiring, includes an 
electrical contactor mechanism including separable contacts and an 
operating mechanism for opening and closing the separable contacts; an 
overload relay mechanism operatively associated with the electrical 
contactor mechanism for controlling the operating mechanism using the 
control signals; a first terminal mechanism for interfacing the control 
signals to the overload relay mechanism; a modular surge suppressor 
circuit at least for suppressing a surge associated with the control 
signals, with the modular surge suppressor circuit including a second 
terminal mechanism for engaging the first terminal mechanism and 
interfacing the control signals thereto, and also including a third 
terminal mechanism for interfacing the control signals to the second 
terminal mechanism; and a modular terminal block mechanism for engaging 
the control wiring and interfacing the control signals to the third 
terminal mechanism. 
It is an object of the present invention to provide a modular surge 
suppressor which can be installed without hand wiring.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As employed herein, the term "control signals" shall expressly include, but 
not be limited to control voltages, control currents and/or other 
electrical control signals. 
As employed herein, the term "control wiring" shall expressly include, but 
not be limited to any circuit or conductor providing electrical 
interconnection of control signals such as, for example, insulated or 
non-insulated conductors, wires, cables or bus bars. 
As employed herein, the term "terminal" shall expressly include, but not be 
limited to an electrical connection point for control wiring such as, for 
example, input terminals, output terminals, male terminals, female 
terminals, or terminals for mating or engaging other terminals. 
Referring to FIG. 1, an isometric view of a modular contactor 2, overload 
relay 4, surge suppressor 6 and terminal block 8 are illustrated. As shown 
in FIG. 1 and as explained in greater detail below with FIGS. 5-7, the 
terminal block 8 engages the surge suppressor 6 which, in turn, engages 
the overload relay 4 which, in turn, engages the contactor 2. FIG. 2 
illustrates the modular contactor 2, overload relay 4 and surge suppressor 
6 with the terminal block 8 of FIG. 1 removed. FIG. 3 illustrates the 
modular contactor 2 and overload relay 4 with the terminal block 8 
engaging the overload relay 4 in place of the surge suppressor 6 of FIG. 
1. FIG. 4 illustrates the modular contactor 2 and overload relay 4 with 
the surge suppressor 6 and terminal block 8 removed. The modular contactor 
2 and overload relay 4 are disclosed in greater detail in concurrently 
filed, commonly assigned, copending Application Ser. No. 08/558,634, 
entitled "Motor Control System". 
Referring to FIG. 5, a block diagram and schematic of the interface to the 
terminal block 8 and surge suppressor 6 is illustrated. A control voltage 
10 (e.g., a line voltage) is connected to two conductors 20,22. The 
control voltage 10 is derived by an external transformer (not shown) from 
the power line phases (not shown) of the contactor 2, although the present 
invention is applicable to any direct current or alternating current 
control voltage associated with one or more power line phases. A 
conventional motor starting circuit 11 includes a normally open start 
switch 12, a normally closed stop switch 14, and a normally open contact 
16 which is closed in order to seal-in the start switch 12 whenever a load 
(not shown) such as a motor powered through the contactor 2 is energized. 
As understood by those skilled in the art, the circuit 11 provides a 
control signal R (e.g., RUN) on conductor 18, although the present 
invention is applicable to any direct current or alternating current 
control signal. Whenever the switches 12, 14 are both closed, the voltage 
of the control signal R is the same as the control voltage 10 and the 
voltage E (e.g., ENABLE) of the conductor 20. The voltage C of the return 
conductor 22 is a voltage common which is referenced to ground 24, 
although the invention is applicable to isolated control voltages. In this 
manner, the control signal R and the voltage E, which is the same as the 
control voltage 10, are both referenced to the ground 24. 
The terminal block 8 includes a plurality of input terminals 26 which 
engage the conductors 18,20,22 and a plurality of output terminals 28 
which engage a corresponding plurality of input terminals 30 of the surge 
suppressor 6. The surge suppressor 6 includes a plurality of output 
terminals 32 which engage a corresponding plurality of input terminals 34 
of the overload relay 4 which, in turn, engages the contactor 2 at an 
interface 36. As explained in greater detail below with FIG. 11, the surge 
suppressor 6 conditions the voltages R,E,C and/or suppresses surge 
voltages or transients thereon. The modular terminal block 8 forms a 
mechanism for interfacing the conductors 18,20,22 with the modular surge 
suppressor 6, although the invention is applicable to a wide variety of 
other termination mechanisms for engaging control wiring such as, for 
example, compression terminals, screw terminals and ring lug terminals. 
Referring to FIGS. 6 and 7, isometric views of the surge suppressor 6 and 
terminal block 8 are illustrated with the terminal block 8 respectively 
separated from and installed into the surge suppressor 6. The terminal 
block 8 includes a plurality of input terminals 26R,26E,26C which engage 
the conductors 18,20,22, respectively. As shown with the input terminal 
26C and conductor 22, each of the input terminals 26R,26E,26C includes a 
screw 38 for compressing a compression terminal (not shown) in a 
compression terminal socket 40 which engages one of the conductors 
18,20,22, respectively. The screws 38 and sockets 40 form a screw terminal 
mechanism for engaging control wiring 42 which includes the conductors 
18,20,22, although the invention is applicable to a wide variety of 
termination techniques for a wide range of conductive circuits. The 
exemplary terminal block 8 also includes a plurality of output terminals 
28C,28E,28R (shown in hidden line drawing) which engage a plurality of 
input terminals 30C,30E,30R, respectively, of the surge suppressor 6. The 
surge suppressor 6 also includes a plurality of output terminals 
32C,32E,32R which respectively engage a plurality of input terminals 
34C,34E,34R of the overload relay 4 of FIG. 4. As shown with FIGS. 1-4 and 
6, both sets of input terminals 30C,30E,30R; 34C,34E,34R are designed to 
engage the output terminals 28C,28E,28R of the terminal block 8. 
Referring to FIGS. 6 and 8-10, the exemplary surge suppressor 6 includes a 
plastic cover 44, a plastic base 46 and a printed circuit board assembly 
48 which is secured between the cover 44 and base 46, although the present 
invention is applicable to surge suppressors having a wide variety of 
packages and circuit assemblies that support both input terminals for 
interfacing a termination mechanism and output terminals for interfacing 
an electrical switching device. The printed circuit board assembly 48 
includes a printed circuit board 50, a male plug 52 having the output 
terminals 32C,32E,32R, a female header 54 having the input terminals 
30C,30E,30R (shown in FIG. 6), a capacitor 55, and resistors 56,57. 
As shown in FIG. 4, the input terminals 34C,34E,34R of the overload relay 4 
are housed in a female header 58. The output terminals 28C,28E,28R of the 
terminal block 8 of FIG. 6 are housed in a male plug 60 which engages the 
female header 58 of the overload relay 4 or the female header 54 of the 
surge suppressor 6. Both of the exemplary female headers 54 and 58 have 
three male terminals 59 which engage corresponding female terminals 61 of 
the male plugs 60 and 52,60, respectively (as shown in phantom line 
drawing with the male plug 52 of FIG. 10). 
Referring to FIGS. 4 and 7, each of the male plugs 52 and 60 have a pair of 
tabs 62 which engage (as shown in FIG. 7) a shoulder 63 of the female 
headers 58 and 54,58, respectively. In this manner, the tabs 62 and 
shoulder 63 provide a mechanical locking mechanism for securably engaging 
the output terminals 32C,32E,32R of the surge suppressor 6 to the input 
terminals 34C,34E,34R of the overload relay 4 by locking the male plug 52 
to the female header 58 when the terminals 32C,32E,32R; 34C,34E,34R are 
engaged. Similarly, the tabs 62 and shoulder 63 also provide a mechanical 
locking mechanism for securably engaging the output terminals 28C,28E,28R 
of the terminal block 8 to the input terminals 30C,30E,30R of the surge 
suppressor 6 (e.g., FIGS. 1 and 7) or, alternatively, to the input 
terminals 34C,34E,34R of the overload relay 4 (e.g., FIG. 3). 
Also referring to FIG. 11, a circuit 64 for suppressing a surge associated 
with the conductor 20 for the voltage E includes the series combination of 
the capacitor 55 and resistor 56 which form an exemplary R-C snubber 
circuit, although the invention is applicable to a wide variety of surge 
suppressors such as fuses and other current interrupting devices, current 
limiting devices such as resistors, inductors or positive temperature 
coefficient (PTC) resistive elements, varistors, zener diodes, low-pass 
filters, band-pass filters and other surge suppressing or voltage 
conditioning devices and/or circuits. The circuit 64 is electrically in 
parallel with the control voltage 10 of FIG. 5. The control voltage 10 is 
interconnected with the circuit 64 by the conductors 20,22, input 
terminals 26E,26C, output terminals 28E,28C, input terminals 30E,30C and 
printed circuit conductors 65,66, respectively. The printed circuit 
conductors 65 and 66 include the control signals E and C, respectively. 
A circuit 67 for biasing the control signal R on printed circuit conductor 
68 includes the resistor 57 which is electrically interconnected between 
the printed circuit conductors 68,66, the input terminals 30R,30C and the 
conductors 18,22, respectively. In this manner, the control signal R, as 
output by the output terminal 32R, is biased by the resistor 57 to the 
control signal C. In this manner, the impedance between the conductors 
66,68 is lowered and, thus, the susceptibility of the control signal R to 
noise and/or surge waveforms is reduced, although the invention is 
applicable to other biasing techniques such as a resistor between a 
voltage signal and a control signal. 
As shown in FIG. 11, an exemplary surge suppressor circuit 69, formed by 
the circuits 64,67, suppresses a surge associated with the control signal 
E and, also, biases the control signal R of the control wiring 42. The 
circuit 69 is interfaced by the output terminals 32R,32E,32C to an 
electrical switching device 70 such as the exemplary contactor, although 
the invention is applicable to a wide variety of electrical switching 
devices and circuit interrupters such as, for example, a circuit breaker, 
contactor or motor starting contactor such as the contactor 2 and overload 
relay 4 of FIGS. 1-4. 
The exemplary electrical switching device 70, which is adapted to be 
controlled through the control signals R,E,C in the control wiring 42, 
includes separable contacts 72 and an operating mechanism 74 for operating 
the separable contacts 72. The exemplary operating mechanism 74 includes a 
coil 76 and a switch (SW) 78 which is controlled by the control signal R. 
When the control signal R is active, the switch 78 is turned on and the 
coil 76 is energized by the control voltage between the control signals E 
and C. In turn, the coil 76 closes the separable contacts 72 as understood 
by those skilled in the art. On the other hand, when the control signal R 
is inactive, the switch 78 is turned off, the coil 76 is de-energized and 
the separable contacts 72 are open. The electrical switching device 70 
also includes an electrical connection mechanism 34' having input 
terminals 34R',34E',34C', such as the input terminals 34R,34E,34C of the 
female header 58 of FIG. 4, for interfacing the respective control signals 
R,E,C in the control wiring 42 to the operating mechanism 74. 
As discussed above with FIG. 5, the surge suppressor 6 may, alternatively, 
interface a motor starter 80 formed by the contactor 2 and overload relay 
4. The overload relay 4 includes a control circuit 82 having a current 
sensor (CS) 84. The contactor 2 includes a coil 86 for controlling 
separable contacts 88. The overload relay control circuit 82 is 
operatively associated with the electrical contactor 2 through the 
interface 36 and controls the coil 86. The coil 86 forms an operating 
mechanism for opening and closing the separable contacts 88. The current 
sensor 84, such as a current transformer or other current sensing device, 
monitors the current flowing through the separable contacts 88. In this 
embodiment of the invention, the control signals R,E,C in the control 
wiring 42 are received by the control circuit 82 which, in turn, controls 
the contactor coil 86 using the control signal R. The control circuit 82 
also provides power to the contactor coil 86 using the control signals E,C 
in the control wiring 42. 
While specific embodiments of the invention have been described in detail, 
it will be appreciated by those skilled in the art that various 
modifications and alternatives to those details could be developed in 
light of the overall teachings of the disclosure. Accordingly, the 
particular arrangements disclosed are meant to be illustrative only and 
not limiting as to the scope of the invention which is to be given the 
full breadth of the appended claims and any and all equivalents thereof.