Note: Descriptions are shown in the official language in which they were submitted.
23
ELECTRIC SAFETY SUPPLY APPARATUS AND CONNECTOR DEVICE
COMBINATION
FIELD OF THE INVENTION
The present invention relates to safe grounding of
the electrically conducting housing of an electrical
appliance.
BACKGROUND OF THE INVENTION
Many devices have been proposed for safely
grounding the housing of an electrical appliance, one of
these devices is described in Canadian Patent No. 1,074,000
issued March 18, 1980 to HELWIG. This known apparatus
comprises a cordless electrical appliance, an adaptor unit
for the appliance, and a base unit. The base unit is
provided with supply-voltage-connection contacts for
connection to a supply voltage, and with two appliance-
current-supply contacts. The base unit also includes an
appliance-current-path connected between the supply--voltage-
connection contacts and -the appliance-current-supply
con-tacts. In the base unit, a step down transformer with a
secondary winding produces an auxiliary, low amplitude
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23
current, flowing ~hrough an auxiliary-current-path when a
pair of auxiliary contacts are electrically interconnec-ted,
one of these auxiliary contacts being grounded. ~ relay is
responsive to the auxiliary, low amplitude current in its con-
-trol winding to close a relay switch connected in the appli-
ance-current-path. The adaptor unit is provided with two
appliance-current-supply contacts electrically connected to
the internal, load circuit of the electrical appliance, and
with a pair of auxiliary short-circuited contacts respectively
engageable with the auxiliary contacts of the base unit for
interconnecting the said pair of auxiliary contacts of the
base unit. The appliance comprises an electrically conducting
housing electrically connected to the short-circuited auxi-
liary contacts. When the adaptor unit is placed on the base
unit, the appliance-current-supply contacts of the adaptor unit
engages those of the base unit to supply with electric power
the internal, load circuit of the appliance, the auxiliary
contacts of the base unit are interconnected together to esta-
blish the auxiliary current, and the housing of the electrical
appliance is grounded through the said grounded one of the
auxiliary contacts of the base unit, and through the auxiliary
contact of the adaptor unit connëcted to the latter grounded
auxiliary contact of the base unit.
Although the above described prior art device per-
mits to check appropriate connection between the auxiliary
contacts of the base and adaptor unit, it cannot detect dis-
connection of the housing of the electrical appliance from
the short-circuited auxiliary contacts, and therefore from
the ground.
OBJECTS OF THE INVENTION:
It is an object of the present invention to provide
in combination, an electrical appliance comprising an elec-
trically conducting housing, and a safety connector device
for safely grounding the said housing.
It is also an object of the present invention to
-- 2
provide a method for safely groundlng the electrically
conducting housing of an electrical appliance.
SU ARY OF THE INVENTION
According -to the present invention, there is
provided in combination, (a) an electrical appliance
comprising an electrically conducting housing to be
grounded, and an internal, load circuit, and (b) a safety-
connector device comprising an electric plug with at least two
first,power contacts through which the said internal, load
circuit can be energized, andtwo second auxiliary contacts
respectively connected to two separate points of the said
housing so that the said two auxiliary contacts are
interconnected together by an interconnecting circuit
including the said housing, a first one of the two second
contacts being connectable to a ground for grounding the
said housing whereby a disconnection of the said ground from
the said housing can be detected by sensing a discontinuity
in the said interconnecting circuit.
The combination according to -the invention may
further comprise a protective supply apparatus for sa~ely
coupling an electric power source provided with said ground
and with at least two power terminals to the said internal,
load circuit of the electrical appliance via the said safety
connector device, comprising:
- input contact means including at least two
third, power contacts to be respectively connected to the
said at least two power terminals, and a Eourth, ground
contact to be connected to the said ground of the power
source;
- a first outlet in which the electric plug of the
said safety connector device can be inserted, said first
outlet having at least two fifth, power contacts
respectively connected to the sald at least two first
contacts when the said electric plug .is inserted in the said
first outlet, and two sixth auxiliary contac-ts respectively
connected to the said two second contac-ts when the said
electric plug is inserted in the said first outlet, a first
one of said two sixth contacts, connected to the said first one of the
second, auxiliary contacts connectable to the said ground,
being connected to the said fourth, ground contactt for
grounding the said electrically conducting housing;
- a first current path circuit for connecting the
said at least two third power contacts to the said at least
two fifth, power contacts,respectively;
- a step down transformer means having a primary
winding connected between the said at least two power termi-
nals of the said source, and a first secondary winding having
two winding terminals;
- a second current path circuit for
connecting the two terminals of the said first secondary
winding to the said two sixth, auxiliary contacts,
respectively, so that when the said electric plug of the
safety connector device is inserted in the said first
outlet a low amplitude current generated through the first
secondary winding flows through the said second current path
circuit, through the said second and sixth, auxiliary
contacts and through the said interconnecting circuit
including the electrically conducting housing of the
electric appliance; and
- a first relay means having (i) a first control
coil connected in series with the said second current path
circuit, so that the said low amplitude current flows
through said first control coil and (ii) first normally
open switch means connected in series with the said first
current path circuit, closed when the said low amplitude
current flows through the first control coil so that the two
third contacts are connected to the two fifth contacts,
~3
respectively, and the i.nternal, load circuit of the elec-
trical appliance supplied with electric current from the power
source through the third contactslthe first current path cir-
cuit, and the ~irst and fifth contacts, and opened in respon-
se -to a discontinuity in the said interconnecting circuit in-
cluding the said housing, which discontinuity can be caused
by disconnection of the said electrically conducting housing
from the ground of the power source and interrupts the low
amplitude electric current to open the first normally open
switch means whereby the first current path circuit is opened
and the internal, load circuit of the said appliance is de-
activated.
According to another aspect of the present invention,
there is provided a method for safely grounding an electri-
lS cally conducting housing of an electrical appliance by connect-
ing the said housing to a ground of an electric power source,
comprising the steps of:
- connecting the said ground to a first point of the
said housing via first contact means;
- connecting second contact means to a second point
of the said housing, the said second point being different
froln the said first point so that the said first and second
contact means are interconnected through an interconnecting ~:
circuit including the said housing;
- establishing a low amplitude electric current
through the second contact means, the said interconnecting
circuit and the first contact means; and
- detecting the said low amplitude electric curren-t,
detection of the said low amplitude electric current being
indicative of electrical interconnection of the first and
second contact means through the interconnecting circuit
including the said housing, and consequently of a safe con-
nection of the housing of the electrical appliance to the
ground of the said power source.
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The objects,advantages and other fea-tures oE the
present invention wi.ll become more apparent upon reading o:E
the followin~ non restrictive description oE preferred
embodiments thereof, given for the purpose of
exemplification only with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 represents, in a schematic diagram form,
an embodiment of an electrical appliance, a safety connector
device and a protective supply apparatus in combination
according to the present invention;
Figure 2 represents, in a schematic diagram form,
another embodiment of an electrical appliance, a safety
connector device, and a protective supply apparatus in
combination according to the present invention;
Figure 3 represents, in a schematic diagram form,
a three phase embodiment of an electrical appliance, a
safety connector device and a protective supply apparatus in
combination according to the present invention; and
Figure 4 represents, in a schematic diagram form,
a further embodiment of an electrical appliance, a safety
connector device and a protective supply apparatus in
combination according to the present invention.
DETAILED D~SCRIPTION OF THE PREFERRED EMBODIMENTS
In figure 1, there is illustrated in combination,
an electrical appliance 2 comprising an electrically
conducting housing to be grounded and an internal, load
circuit 15, and a safety connector device 8 comprising an
elec-tric plug. The electric plug has two power contacts 10
through which -the internal load circuit 15 is energized, and
two auxiliary contacts 12. The two auxiliary contac-ts 12
are respectively connected to two separate points of the
23
electrically conductlng housing so that these two allxi.li.ary
contacts 12 are intercon~ec-ted -together through an
interconnecting ci.rcuit 6 including the elec-trically
conducting housing. The one 30 of the ~iliary contacts 12 of Fig~re 1 is
connectable to a ground for grounding-the housing whereby aclisconnec-tion
of the ground from ~he housing càn be detected by sensing a discon-tinuity
in the interconnection circuit 6 including the housing of
the appliance.
As shown in figure 1, a protective supply
apparatus 18 safety couples a power source (not shown)
provided with a ground to the load circuit 15 of the
electrical appliance 2 via -the safety connector device 8.
The protective supply apparatus 18 comprises input contact
means 20 having two power contacts 22 to be respectively
connected to two power terminals of the source and a ground
contact 24 to be connected to the ground of the power
source. The protective supply apparatus also comprises a
first, second and third outlet having respectively two first
26, two second 46 and two third 48 power contacts, and two
first 28, two second 50 and two third 52 auxiliary con-tacts.
A first one 30 of each pair of first 28, second 50, and
third 52 auxiliary contacts is connected to the ground
contact 24. A first 32, a second 54 and a third 56 power
current path circuits connect respectively the two first 26,
the two second 46 and the two third 48 outlet power contacts
to the input power contacts 22.
The protective supply apparatus 18 further
comprises a step down transforrner 34 having a primary
winding 35, having its two terminals respectively connected
to the two input contacts 22. The transformer 34 also
comprises a secondary winding 36. The ratio of -the
transformer 34 is selected so that a voltage of low
amplitude is produced accross the winding 36 in response to
-the voltage between the contacts 22 supplied to the primary
7~3
winding 35. A first 38, a second 58 and a third 60 low
amplitude current path circui-t respectively connect the two
first 28, the two second 50 and the two -th.ird 52 au~iliary
con-tacts to the two terminals of the secondary wi.nding 36.
A firs-t 40, a second 62 and a -third 64 relay
respectively comprise a first 42, a second 66 and a third 68
control coils respectively connected in series with the
first 38, the second 58 and the -third 60 low amplitude
current path circuits, and a first 44, a second 70 and a
third 72 pairs of normally open switches are respectively
connected in series with the first 32, the second 54 and the
third 56 power current path circuits.
A fourth relay 74 is provided with a fourth
control coil 76, the first one 30 of each pair of auxiliary
contacts 28, 50 and 52 being connected to the input, ground
contact 24 via the fourth control coil 76. The fourth relay
74 is also provided with a pair of normally closed switches
78, the pair of input power contacts 22 being connected to
each pair of outlet power contacts 26, 46 and 48 via the
pair of normally closed switches 78. As can be seen the
power contacts 22 are also connected to the primary winding
35 of the step down transformer 34 via the pair of normally
closed switches 78.
A light bulb 37 is connected in parallel with the
secondary wi.nding 36 to indicate energizing of the step
down transformer 34. A light bulb 43 in series with a
norrnally open switch 45 of the relay 40 is connected in
parallel with the first control coil 42 and is energized in
response to closure of the switch 45 to indicate energizing
of -the coil 42 and closure of the switches 44, a light bulb
67 in series with a normally open switch 65 of the relay 62 is
connected in parallel with the coil 66 and is energized in
response to closure of the swi-tch 65 -to indicate energizing
of the coil 66 and closure of the switches 70, and a light
-- 8
bulb 69 .in series with a normally open switch 71 oE the
relay 64 is connec-ted in parallel with the control coil 68
and is energized in response -to closure oE the switch 71 to
indicate energiging of the coil 68 and closure of -the
swi-tches 72.
The protective supply apparatus is also provided
with fuses 1 for the protection oE certain components of
this apparatus. Two fuses 1 are connected in series with
the primary winding 35 of the step down transformer 34,
while two other fuses 1 are connected in series with the
secondary winding 36 of the step down transformer 34. Other
fuses 1 are connected in series with each of the low power
current path circuits 38, 58 and 60.
When the electric plug of -the safety connector
device 8 is inserted in one of the outlets of the supply
apparatus 18, the power contac~s 10 of the plug are
connected to the power contacts 26, 46 or 48 of the outlet
and the auxiliary contacts .12 of the plug are connected to
the auxiliary contacts 28, 50 or 52 of the outlet with the auxiliary con-
zo tacts identified by the reference 30 connected together. Accordingly,
a low amplitude current flows through the low amplitude current path cir-
cuit 38, 58 or 60, the control coil 42, 66 or 68 to close the switches 44,
70 or 72, the auxiliary contacts 28, 50 or 52, the auxiliary contacts 12
of the plug and the circuit 6 including the housing of the
appliance 2 which interconnects the auxiliary contacts 12.
As the switches 44, 70 or 72 are closed,the load circuit 15
of the electrical appliance 2 is supplied with electric
energy from the contacts 22 through the normally closed
switches 78, the current path circuit 32, 54 or 56, the
closed switches 44, 70 or 72, the power contacts 26, 46 or
48 of the outlet, and the power contacts 10 of the plug.
When a discontinuity occurs in the circui-t 6
interconnecting the auxiliary contacts 12 through the
housing of the appliance 2, which discontinuity can be
g
~L~9~
caused by disconnection oE this houslng from the auxiliary
contact 30 of the plug and -therefore from the ground con-tac-t
24, resulting in unappropriate groundi.ng of -the housing which
can be dangerous for the user of the appliance, the low ampli-
tude current path circuit 38, 58 or 60 is opened so that the
control coil 42, 66 or 68 is de-energized, the switches 44,
70 or 72 are opened to open the corresponding current path
circuit 32, 54 or 56, and the load circuit 15 of the elec-
trical appliance is de-energized. Moreover, a fault detec-
tion switch 14 is responsive to a fault in the circuit 15
to produce a discontinuity in the circuit 6 interconnecting
the two contacts 12 so that the load circuit 15 of the
electrical appliance is deactivated as explained hereinabove.
Upon occurrence of a fault causing application
of a voltage to the housing of the electric appliance, which
application of voltage can be dangerous for the user of
the electrical appliance 2, a high amplitude ground fault
current flows through the housing of the appliance 2, the
one 30 of the auxiliary contacts 12 of E'igure 1, the one
30 of the contacts 28~ 50 or 52 of the outlet, and the con-
trol coil 76 of the relay 74. The ground current in the
coil 76 causes opening of the normally closed switches 78,
whereby both the supply apparatus 18 and the appliance 2
are de-energized to eliminate the situation dangerous for
the user.
OE course, an electrical appliance such as 2 can
be connected to each of the outlets oE the apparatus 18
through its safety connector device 8.
The protective supply apparatus 18 also comprises
a frame enclosure 124, three covers (not shown) advanta-
geously hinged on the frame enclosure 124 for covering
the three outlets, respectively, a first push button me-
chanically operated by the cover of the first outlet and
comprising two switches 126, 126' closed when the cover is
-- 10 --
open and open when the cover i.s closed, a second push button
mechanically operated by the cover of -the second outle-t and
including two switches 128, 1287 which are closed when -the
cover is open and open when the cover is closed, and a
third push button mechanical.ly operated by the cover of the
third outle-t and including two switches 130, 130' both closed
when the cover is open and both open when the cover is closed.
Accordingly, the transformer 34 works only when one of the
three covers is opened to close one of the switches 126',
128' and 130', and thereby to supply the primary winding
35 with electric energy through the closed switch 126',128'
and/or 130'. In the same manner, the controlcoils 42,
66 and 68 can be energized only when the corresponding ones
of the three covers are opened to close the associated switches
126, 127 and 128 disposed on the low amplitude current path
circuits 38, 58 and 60, respectively. When all of the
covers are closed, the switches 126, 126', 128, 128', 130
and 130' are open, whereby no supply of the primary winding
35 nor of the control coils 42, 66 and 68 is possible, thereby
preventing closure o-f the switches 44, 70 and 72 and ener-
gizing oE the power contacts 26, 46 and 48.
Figure 2 illustrates another embodiment of the
invention comprising in combination, an electrical appliance
2 and a safety connector device 8 both similar to those of
Figure 1, and a protective circuit apparatus 18 generally
similar to that of Figure 1 for safely coupling a power sour-
ce (not shown) to the electrical appliance 2. Most of the
elements of Figure 2 correspond to analogous ones of Figure
1 and are therefore identified by the same reference numerals.
The step-down transformer 34 of the protective
supply apparatus 18 of Figure 2 comprises a first 36', a se-
cond 90 and a third 92 secondary winding :Eor respectively
supplying a first, second and third low amplitude voltage.
The first 38, second 58 and third 60 low amplitude current
path circuits connect respectively the two termina]s oE the
secondary windings 36', 90 and 92 -to the pairs oE au~iliary
contac-ts 28, 50 and 52. The protec-tive supply apparatus 18
also comprises relays 110, 111 and 113 having respec~ive
control coils 112, 114 and 116. The con-tacts 30 oE the
pairs of auxiliary contacts 28, 50 and 52 are connected to
the ground contact 24 via the control coils 112, 114 and
116, respectively. The relays 110, 111 and 113 further
include a respective pair of normally closed switches 118, 120 and
122. The pairs of power contacts 26, 46 and 48 are
connected to the pair of power contac-ts 22 via respectively
the switches 118, 120 and 122. When the plug (contacts 10
and 12) of the electrical appliance is inserted in one of
the outlets, (contacts 26 and 28, ~6 and 50, or 48 and 52),
and a ground, fault current from the housing of the
appliance 2 flows through the contact 30 of the auxiliary
contacts 28, 50 or 52, and the control coil 112, 114 or 116,
the switches 118, 120 or 122 open to de-energizing the
electrical appliance.2 by opening the current path circuit
32, 54 or 56.
The two power contacts 22 are, in the embodiment
of Figure 2, connected to the prim~ry winding 35 directly through
the switches 126', 128' and 130', and a pair of fuses 1.
Light bulbs 37' are connected in parallel to each of the
secondary windings 36', 90 and 92 for individually
indicating that the corresponding secondary winding is
energized.
The embodiment of Figure 2 presents the advantage
that, when an electrical appliance is connected to each
outlet of the protective supply apparatus, and when a fault
connection happens be-tween the power contacts 10 of the
safety connector device of one of the electrical appli.ances
and the housing of the latter appliance, only this
electrical appliance is then deactivated. The two other
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~2~23
electrical appliances remaln energized.
Figure 3 illustrates another embodiment of the
invention comprising in combination, a three phase electric
appliance 2, a three phase safety connector device 8 and a
5 three phase protective supply apparatus 18 Eor safely
coupling a three phase power source (not shown) to the -three
phase, load circuit 15 of the electrical appliance 2. The
elements of Figure 3 which correspond to analogous ones of
Figures 1 and 2 are identified by the same reference
10 numerals.
In the embodiment of Figure 3, the safety
connector device comprises three power contacts 10', and the
protective supply apparatus lB comprises three power input
contacts 22' to be respectively connected to the three
15 phases of the power source (not shown), and an outlet with
three power contacts 26' to be respectively connected to the
three power contacts 10' of the safety connector device 8.
A relay 40 comprises three normally open switches 44'
connected between the three power input contacts 22' and -the
20 three power outlet contacts 26'.
Three light bulbs 93 are connected between each
couple of power contacts 26' for indicating that the
electrical appliance 2 is appropriately energized.
In Figure 3, the prirnary winding 35 of the step-
25 down transformer 34 is connected though a pair of fuses 1between two ones of the contacts 22'. The secondary winding
36 of the transformer 34 produces a low amplitude current
flowing through a low amplitude current path circuit 38,
through a control coil 42 of the relay 40 to close the
30 switches 44', to connect the three power outlet contacts 26'
to the three power input contacts 22', respectively, and to
energize the three phase, load circuit 15 of -the
electrical appliance 2 having the plug of its safety
connector device inserted in the outlet of the apparatus
18, and through the eircuit 6 including the elec-trically
eonducting housing of the appli.ance 2 and interconneeting
the two auxiliary eontacts 12. When a ground Eault current
from the housing of the appliance flows through the contaets
30 of Figure 3, and -through a control coil 76' of a relay
74', a normally elosed switeh 78' of the relay 74' open to
interrupt the low amplitude current in the coil 42, to open
the switehes 44' and to de-energize the three-phase electri-
cal appliance 2. The coil 42 is also de-energized and the
switches 44' opened when the circuit 6 opens, which may indi-
cate ungrounding of the appliance housing.
The embodiment of Figure 4 comprises in combina-
tion, an electrical appliance 2 similar to that of Figures
1 and 2, a safety connector device 8 simllar to that of
Figures land 2, and a pro-teetive supply apparatus 18 for
safely coupling a power source (not shown) to the load eir-
euit 15 of eleetrieal applianee 2. Most of the elements
of Figure 4 correspond to analogous ones of Figure 1 and
are identified by the same referenee numerals.
In the embodiment of Figure 4, the pair of power
input eontaets 22 are eonneeted -to the primary winding 35
of the step-down transformer 34 to energize the same. The
seeondary winding 36 has one 78 of its two terminals eonneet-
ed -to one termi.nal 80 of the eontrol winding 88 of an
eleetromeehanical relay 86 and the other 82 of its two
terminals conneeted to one eontae-t 84 amongst the pair of
auxiliary contae-ts 28 via the eontrol eoil 42 of the relay
40. The relay 86 is also provided with a normally elosed
switeh 91 eonneeted in series with the eurrent path eireui-t
32. The eontaet 30 of the pair of auxiliary eontaets 28
is eonneeted -to the ground eontaet 24 via the eontrol. eoil
88 and the low ampli-tude eurrent path eircuit 38. When the
plug (eontacts 10 and 12) of the electrical appliance 2
is inserted in the outlet (con-tacts 26 and 28) of the appa-
., - 14 -
723
ratus 18, a low amplitude current produced by the secondary
winding 36 Elows through the low current pa-th circui-t 38,
through the interconnec-ting circuit 6, through -the con-tacts
12 and 28 and through the con-trol coil 42 to close a normally
open switch 44'' oE the relay 40 and thereby energize the
electrical appliance 2 -through the curren-t path circuit 32.
Upon supply of a ground fault electric curren-t from the
electrically conducting housing of the appliance 2 to the
coil 88 -through the auxiliary contacts 30 and -the current
path circuit 38, the normally closed switch 91 opens to
deactivate the electrical appliance 2.
Of course, a discontinuity in the interconnecting
circuit 6 of Figure 4 interrupts the low amplitude current,
de-energizes the coil 42, opens the switch 44'', and deacti-
vates the load circuit 15, which discontinuity can be caused
by disconnection of the appliance housing from -the ground.
The protective supply appara-tus ]8 of Figure 4 is
also provided with a light bulb 93 connected between -the po-
wer contacts 26 for indicating that the electrical appliance
2 is energized.
It can be appreciated that the above described
embodiments of the present inven-tion carry out a method of
safely grounding the electrically conducting housing of an
electrical appliance by connec-ting the housing to -the ground
oE a power source. The me-thod comprises the step of connect-
ing the ground to a first point oE the housing via a first
contact means, and connecting a second contact means to a
second point oE the housing. The second point is different
from the first point so that -the firs-t and second contact
means are interconnected via an interconnecting circuit in-
cluding the housing. The method also comprises the steps of
establishing a low amplitude electric current through the
first and second contact means and the circuit in-terconnect-
ing these first and second con-tact means, and detecting the
low amplitude electrical current. Detec-tlon oE -the latter
current ls indicative of the elec-trical interconnectlon of
the first and second contact means through the in-terconnec-
tion circui-t including -the housing, and consequen-tly of a
safe connection of the housing of the electrical appliance
to the ground of the power source. The method also comprises
the step of energizing the electrical appliance upon detec-
tion of the low amplitude current.
Although the present invention has been described
hereinabove by way of preferred embodiments thereof, it
should be pointed ou-t that any modification to such pre-
ferred embodiments, within the scope of the appended claims,
is not deemed to alter the nature and scope of the invention.
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