Motor starting switch with dual load disconnect

A motor starting switch including a pair of auxiliary switches operable in response to the stopping of the drive motor of an electrical appliance or the like for disconnecting both sides of an electrical load in the appliance (e.g., for disconnecting a heating element) from the input power lines thereby to reduce shock and fire hazards of the appliance due to a short circuit of the load when the appliance is turned off, and for automatically connecting the load to the input lines of the appliance in response to start up of the motor.

BACKGROUND OF THE INVENTION 
This invention relates to a safety switch for disconnecting both sides of 
an electrical load in an electrical appliance from the power lines of the 
appliance thereby to reduce both shock and fire hazards when the appliance 
is turned off in the event of a short circuit of the load. More 
specifically, this switch is a combination motor starting switch and load 
disconnect switch operable by a centrifugal actuator which is typically 
included in the appliance drive motor. 
As is conventional, the wiring system in a house or other building is such 
that at any outlet, one of the outlet leads is connected directly to the 
power line coming into the house and the other lead is connected to an 
electrically grounded return line. Switches for appliances or the like 
typically operate by making or breaking either the power input lead or the 
ground lead. In connecting most appliances to a home wiring system, it is 
difficult to determine which lead is the power input lead and which is the 
return lead, and many appliances it will operate satisfactorily no matter 
how the appliance is wired to the input and return leads. In certain 
instances with the on-off switch of an appliance (for example, the timing 
switch of an electric clothes dryer or the like) making or breaking the 
grounded return lead of the appliance, a mechanical or electrical failure 
of the load could short circuit the load to ground thus creating a shock 
or fire hazard in the appliance even though the appliance is turned off. 
This danger is especially apparent in such electrical appliances as 
electric clothes dryers in which the breakdown of the insulator supporting 
the heating element, or the breakage or sagging of the heating element 
wires, could result in a short circuit of the heating element to ground. 
Further, in such appliances as electric clothes dryers powered by 230 volt 
current, it will be appreciated that both power input leads are "hot" so 
that a failure of the heating element could cause a 115 v. short to ground 
through the element. Heretofore, motor starting switches for the drive 
motor of the appliance were known which not only effected energization and 
deenergization of the starting winding of the drive motor upon start up 
and shut down of the motor, but also, certain of these motor starting 
switches disconnected one side or the other of an electrical load from one 
of the power lines of the appliance. However, since only one side of the 
load was disconnected from the load lines, in many instances the load 
would still be connected to the power input lead so that in the event of a 
failure of the load to ground, a short circuit of the load could occur. 
Reference may be made to the co-assigned U.S. Pat. No. 4,034,173 which 
discloses a motor starting switch in the same general field as the switch 
of this invention and to the co-assigned U.S. patent application Ser. No. 
938,455 filed Aug. 30, 1978, now U.S. Pat. No. 4,240,001. 
SUMMARY OF THE INVENTION 
Among the several objects and features of this invention may be noted the 
provision of a switch operable in response to the stopping of the drive 
motor of an appliance for disconnecting both sides of an electrical load 
from the input and return leads of the appliance thereby to reduce both 
shock and fire hazards of the appliance when the latter is off and for 
automatically reconnecting the load to the input and return lines of the 
appliance upon start up of the drive motor; 
The provision of such a switch which is readily actuable by the centrifugal 
actuator of the drive motor of the appliance and which requires only a 
relatively low actuation force; 
The provision of such a switch which positively opens and holds open its 
contacts for breaking connection to the load upon stopping of the drive 
motor; and 
The provision of such a switch which may be readily incorporated in the 
appliance, which is inexpensive to manufacture and to install, which is 
reliable in operation, and which is of rugged construction. 
Briefly, a switch of this invention is intended for use in an appliance or 
the like for disconnecting both sides of a load in the appliance from the 
power input lines of the appliance thereby to reduce shock and fire 
hazards in the event the load inadvertantly becomes grounded while the 
appliance is off and for automatically connecting the load to the input 
lines upon start up of the appliance. The appliance has an actuator 
operably movable from an off position to a run position in response to 
start up of the appliance and is further movable from its run to its off 
position in response to stopping of the appliance. The switch comprises a 
switch housing, and a first and a second set of switch contacts for making 
electrical contact between both sides of the load and the input lines in 
response to the actuator moving from its off to its run position and for 
breaking electrical contact between the load and the input lines in 
response to movement of the actuator from its off position. 
Other objects and features of this invention will be in part apparent and 
in part pointed out hereinafter.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings, a combination motor starting/load disconnect 
switch of this invention is indicated in its entirety at reference 
character 1 and it is shown to comprise a housing 3 of molded, synthetic 
resin material, such as bakelite, which is a good electrical insulator. 
Housing 3 has a pair of mounting ears 5 for rigidly mounting the starting 
switch on the end shield or other part of an electric motor. The housing 
is provided with a removable front cover 6 for enclosing sets of 
electrical contacts in the switch housing. 
Switch 1 is intended to be mounted in relatively close proximity to a rotor 
shaft 7 (see FIGS. 3 and 4) of the motor. As is typical, a centrifugal 
actuator, as generally indicated at 9, is mounted on shaft 7 for rotation 
therewith. Generally, this actuator may be similar to any one of a number 
of known centrifugal actuators, such as the actuator shown in the 
co-assigned U.S. Pat. No. 3,609,421. The centrifugal actuator is mounted 
on shaft 7 for rotation therewith and has an actuator member 10 movable in 
axial direction along the shaft from an off position (as shown in FIG. 3) 
when the motor is stopped (or when it is operating below a specified 
speed) and a run position (as shown in FIG. 4) when the motor is operated 
at or above a predetermined speed. Actuator member 10 as shown to have a 
conical actuator face 11 facing toward its off position and an outer 
cylindric face 13 generally parallel to the axis of the rotor shaft and 
contiguous to the outer edge of the conical face. 
As best shown in FIGS. 2-4, a plurality of sets of electrical contacts are 
provided in switch housing 3. In particular, the starting switch 
illustrated in the drawings has a center contact set including a pair of 
spaced, fixed contacts 15a and 15b and a movable contact 17 mounted on a 
resilient, flexible switch arm 19 of spring-like electrically conductive 
metal (e.g., beryllium copper or the like) cantilever supported by switch 
housing 3 and being flexibly movable between the fixed contacts so as to 
constitute a single pole, double throw switch, as is generally indicated 
at 20. For example, fixed contact 15a may be connected to the starting 
winding S of a drive motor M of an electric appliance, such as an electric 
clothes dryer shown schematically in FIGS. 7 and 8. Switch arm 19 is shown 
to be connected to a source of power (e.g., to the load or input line of 
the appliance) so that upon start up of the motor, contacts 15a and 17 
effect energization of the starting winding. As best shown in FIGS. 2, 7 
and 8, switch 1 further includes a pair of single pole, single throw 
switches, as generally indicated at 21a and 21b. Each of these switches 
has a respective fixed contact 25a, 25b and a respective movable contact 
27a, 27b carried on a respective resilient flexible switch arm 29a, 29b 
cantilever supported from the switch housing for flexible movement toward 
and away from its fixed contact for making and breaking a circuit. Switch 
arms 29a, 29b are similar in construction to the above-described switch 
arm 19. In FIGS. 7 and 8, switches 21a and 21b are shown to connect a load 
in the appliance, such as heating element H, to the load lines (i.e., to 
the power input and return lines) L1, L2 of the appliance when closed and 
to disconnect both sides of the load from the load lines when open. Switch 
arms 19, 29a and 29b constitute spring means for biasing their respective 
movable contacts toward a normal or unflexed position (as shown in FIGS. 3 
and 6) in which movable contact 17 is in firm engagement with fixed 
contact 15b and in which movable contacts 27a and 27b are in engagement 
with their respective fixed contacts 25a and 25b. 
The movable contacts and switch arms of switches 20, 21a and 21b are 
movable relative to their respective fixed contacts between a first or off 
position (as shown in FIGS. 3 and 7) and second or run position (as shown 
in FIGS. 4, 6 and 8). In the off position of the switch (i.e., when 
centrifugal actuator 9 is in its off position), contacts 15a and 17 are in 
electrical contact with one another (see FIG. 7) so as to energize 
starting windings of motor M upon start up of the motor and the contacts 
of switches 21a, 21b are open (also see FIG. 7) so as to disconnect both 
sides of heating element H from both load or input lines L1 and L2. Thus, 
in the event of a failure of the heating element, such as a broken or 
sagging heating wire or a failure of the insulators supporting the heating 
element, a short to ground of the power input lead via the broken heating 
element is prevented when the appliance is off thus reducing the shock and 
fire hazards of the appliance. In the run position of switch 1 (shown in 
FIGS. 4 and 8), contacts 15a and 17 of switch 20 are open thereby to 
deenergize start winding S, and the contacts of switches 21a and 21b are 
closed (see FIGS. 6 and 8) thereby to connect by the load (i.e., heater H) 
to the appliance input lines. 
A slider member, as generally indicated at 31, is slidably mounted in 
tracks 33a, 33b provided in housing 3 for sliding along a line of action 
generally parallel to the longitudinal axis of rotor shaft 7 when motor 
starting switch 1 is mounted on a motor in its normally installed 
position. As shown, slider 33 is enlongate member preferably molded of a 
suitable synthetic resin material. It extends from one side of housing 3 
to the other and has cylindrical lugs 35a, 35b at each end thereof for 
reception in respective tracks 33a, 33b. A lever 37 also of synthetic 
resin material is pivotally secured to housing 3, as indicated at 39, for 
swinging in a plane including the longitudinal axis of shaft 7 and the 
line of movement of slider 31. Slider 31 has an integral portion 41 
extending downwardly from the rear portion thereof. Portion 41 is shown to 
be pivotally connected to lever 37, as indicated at 43, at a location 
intermediate pivot connection 39 and the point on the lever it is engaged 
by actuator member 10. This pivotal connection 43 is also referred to as a 
knee. As best shown in FIG. 1, lever 37 is bifurcated with a slot therein 
for reception of portion 41 of slider 31. The lever has an inclined 
surface 45 engageable by conical surface 11 of actuator member 10 as the 
latter moves from its run position toward its off position for swinging 
the lever upwardly or counterclockwise (as shown in FIGS. 3 and 4) so as 
to in turn effect sliding movement of slider 31 in tracks 33a, 33b from 
rear to front of housing 3 and to effect rotation of the slider relative 
to the housing about its cylindric lugs 35a, 35b which fit into the 
tracks. This sliding movement of the slider causes it to engage the outer 
ends of switch arms 19, 29a and 29b and to flex or bend them so as to 
reset or close switch 20 (i.e., to bring movable contact 17 into 
electrical contact with fixed contact 15a) so as to effect energization of 
the starting winding of the motor upon start up of the motor and to open 
switches 21a and 21b (see FIG. 7) thereby to positively disconnect both 
sides of heater H (i.e., the load) from the load lines. 
Upon continued movement of actuator member 10 toward its off position, 
inclined surface 45 of lever 37 will ride up conical face 11 of the 
actuator member so as to effect the above-mentioned swinging movement of 
the lever. Upon the top of the conical surface engaging the bottom edge of 
the inclined face of the lever and upon continued axial movement of 
actuator member 10 toward its off position, the lever will ride up over 
the intersection between conical face 11 and cylindric face 13 of the 
actuator member so that a bottom surface 47 of the lever rides on the 
cylindric surface of the actuator member. Upon the bottom surface of the 
lever engaging the cylindric surface of the actuator member, no further 
swinging of the lever occurs (even though actuator member 10 may continue 
its axial movement) and the relative positions of the lever and the slide 
are maintained fixed so as to in turn hold switch arms 19, 29a and 29b in 
their flexed positions (as shown in FIG. 3). It will be appreciated that 
with the flexible resilient switch arms 19, 29a and 29b so flexed, they 
resiliently bear against the slider and thus constitute means for biasing 
slider 31 rearwardly in housing 3 toward the its position in the housing 
it occupies when the actuator member is in its run position. These switch 
arms further bias lever 37 toward the actuator member 10 and hold it in 
engagement therewith. Thus, upon movement of actuator member 10 from its 
off toward its run position, bottom surface 47 of lever 37 will first move 
clear of cylindric surface 13 of the actuator member, then inclined 
surface 45 of the lever will bear on conical face 11 of the actuator 
member, and finally, upon further axial movement of the actuator member 
toward its run position, the actuator member will move clear of the lever 
altogether. This, of course, allows switch arms 19, 29a and 29b to return 
to their unflexed positions (see FIGS. 4-6) and causes the opening of 
contacts 15a and 17 and the closing of contacts 15b and 17 of switch 20, 
and the closing of switches 21a and 21b. With the above-noted contacts and 
switches closed, the biasing force of switch arms 19, 21a and 29b on the 
slider is relaxed thus ensuring that the full force of the flexible switch 
arms is utilized to keep their respective movable contacts in firm 
electrical contact with their respective fixed contacts. 
It will be noted that lever 37 and slider 31 are preferably moved through 
their entire path of motion by actuator member 10 during only a portion of 
the length of axial travel (or stroke) of the actuator member. More 
specifically, movement of the lever and slider occurs only when inclined 
face 45 of the lever is in engagement with conical face 11 of the actuator 
member and when the latter is moving between its run and off positions. It 
is a particular advantage of switch 1 that it does not matter during which 
portion of the stroke of the actuator member that the inclined face 45 of 
lever 37 rides on conical face 11 of the actuator member so long as the 
lever is moved through its full swing. Accordingly, precise positioning 
and adjustment of switch 1 on the motor with respect to centrifugal 
actuator 9 is not required and switch 1 can therefore accommodate 
relatively large amounts of rotor shaft end play with consequent change of 
the position of the centrifugal actuator with respect to the switch 
without adversely affecting operation of the switch. 
It will also be noted that slider 31 and lever 37 constitute an actuating 
linkage arrangement operable by the centrifugal actuator. Further, this 
actuating linkage is mounted on and carried by switch 1 so that the 
linkage and the switch may be installed on a motor in a single operation 
during manufacture of the motor thus eliminating the necessity of having 
to install a separate linkage after installation of the switch. Also, 
slider 31 and its "knee action" motion efficiently moves switch arms 19 
and 29 in an axial direction substantially parallel to the axial direction 
of the movement of actuator member 10 on rotor shaft 7. Because of the 
relative locations of slider lugs 35a, 35b and of pivots 39 and 43 the 
axial force required of the centrifugal actuator to effect movement of the 
switch arms is quite low in comparison with other known actuator linkages. 
More specifically, lever 37 and slider 31 constitute a toggle linkage. As 
actuator member 10 moves from its run position to its off position and 
engages lever 37, the lever swings upwardly (i.e., clockwise as viewed in 
FIGS. 2 and 3) thus moving pivot point 43 (also referred to as the knee of 
the toggle linkage) closer to an imaginary line between lugs 35a, 35b and 
pivot point 39. As the center or knee pivot moves closer to the 
above-noted imaginary line, the geometry of the linkage changes and a 
force greater than the force exerted on the knee of the linkage is exerted 
on the switch arms. Accordingly, switch 1 is easier to actuate and thus 
effectively avoids many of the "stuck actuator" malfunctions experienced 
by other prior art motor starting switches. 
A spring (not shown) may be provided within housing 3 so as to cooperate 
with the above-mentioned means (i.e., switch arms 19 and 29) for biasing 
the slider and lever 37 toward their respective positions when actuator 
member 10 is in its run position. 
Referring now to FIGS. 7 and 8 switch 1 is diagramatically shown connected 
in a circuit for an electric appliance, such as an electric clothes dryer. 
The circuit includes a timer switch T which opens and closes one of the 
load or input lines (e.g., line L2) of the appliance to start and stop the 
appliance. As shown, timing switch T controls energization of the main 
winding MW of motor M and supplies current to switches 20 and 21a of 
switch 1. With the appliance turned off, timer switch T and switch 1 are 
in their respective off positions, as shown in FIG. 7 and motor M is 
stopped. Switch 20 is shown to be closed, that is, its movable contact 17 
on switch arm 19 is in electrical contact with fixed contact 15a so as to 
energize starting winding S of the motor upon closing of the timing 
switch. Upon the motor accelerating up to a predetermined operating speed, 
centrifugal actuator 9 (not shown in FIGS. 7 and 8) automatically opens 
switch 20 in the manner heretofore described so as to deenergize starting 
winding S. Furthermore, the centrifugal actuator automatically closes 
switches 21 a and 21b so as to connect both sides of heating element H 
(i.e., the load) to load lines L1 and L2 of the appliance. Thus, the 
heating element will remain energized so long as the motor continues to 
operate. Upon timer switch T opening and breaking load line L2, motor M is 
deenergized and begins to stop. Upon motor M slowing below a predetermined 
speed (or upon its stopping), centrifugal actuator 9 moves from its run to 
its off position thus resets switch 20 (i.e., makes contact between 
contacts 15a and 17 of switch 20) and breaks electrical contact between 
contacts 25a, 27a and between contacts 25b, 27b of switches 21a and 21b 
respectively, thereby removing both sides of heater H from the power input 
lines of the appliance when the latter is off. As mentioned above, the 
fact that both sides of the load are disconnected from the input lines of 
the appliance when the appliance is off reduces the shock and fire hazard 
of the appliance due to a short circuit of the load to ground. 
While switch 1 has been disclosed for use with an electric clothes dryer, 
it will be understood that it could be readily used with any appliance or 
electrical device or with any electric motor when it is desired that both 
sides of a load be disconnected from the load lines (or where two or more 
loads are to be disconnected from the load lines) upon shut down of an 
electric motor and be reconnected to the load lines upon start up of the 
motor. Also, other actuators other than a centrifugal actuator may be used 
to operate switch 1. 
In view of the above, it will be seen that the several objects of the 
invention are achieved and other advantageous results attained. 
As various changes could be made in the above construction without 
departing from the scope of the invention, it is intended that all matter 
contained in the above description and shown in the accompanying drawings 
shall be interpreted as illustrative and not in a limiting sense.