Differential switch including a test circuit
The field of the invention is that of protecting electrical installations and persons.
The invention relates more particularly to a differential switch provided with a test circuit for checking that the differential switch is operating correctly.
Differential switches are circuit-breaker devices that can be tripped automatically to open an electrical circuit subject to a current leakage.
If a device in the electrical circuit to be protected has a fault leading to earthing of the live wire of the circuit, a leakage current is created, in the sense that a portion of the electrical current normally flowing in the circuit is diverted to earth.
For obvious safety reasons, it is necessary, and often legally obligatory, to detect the presence of a leakage current of this kind and to break the electrical circuit accordingly. This task is advantageously performed by a differential switch.
Generally, in a differential switch of this kind, conductors connected to the electrical circuit to be protected are generally surrounded by an induction coil and if the current flowing in one direction is different from the current flowing in the opposite direction (which reveals a leakage current in the electrical circuit to be protected), an induced current is created in the coil and feeds an actuator that trips the mechanism, the consequence of which is to open a pair of power contacts and isolate at least one pole of the circuit.
Differential switches generally further include a test circuit for simulating the presence of a leakage current to check that the differential switch trips correctly.
The technique routinely employed to simulate a
leakage current consists in creating within the differential switch a shunt circuit including a resistor one terminal of which is connected to one pole of the electrical circuit to be protected on one side of the induction coil and the other terminal of which is connected to another pole of the electrical circuit to be protected, on the other side of the induction coil. This produces a simulated leakage current that depends on the resistance of the resistor.
The shunt circuit is held open by a test switch, for example a pushbutton switch, which is accessible on the casing of the differential switch so that a user can activate the test function.
Moreover, for improved safety, it is advantageous to provide a mechanism to inhibit the action of the test switch if the differential switch has been tripped.
This is because pressing the test switch when the differential switch has been tripped connects the terminals of the devices of the electrical circuit to be protected to the terminals of the test resistor, which represents a hazard, in particular if these devices store energy, as is the case with a television, for example.
This kind of inhibition of the action of the test circuit is usually called "automatic breaking".
The document EP 0 165 008 discloses a test device of the above kind in which the test pushbutton switch is inhibited by mechanically immobilising the pushbutton when the differential switch has been tripped.
The document EP 0 456 586 describes a test circuit for a differential tripping device including various springs, one of the springs co-operating with a transmission member of the actuator mechanism of the tripping device to open the test circuit when the differential tripping device has been operated.
The document EP 0 295 167 describes a test system
for a differential electrical protection device. The test system includes a conductive blade with two branches, one of the branches providing the test pushbutton switch function and the other branch providing the automatic breaking function on being moved away from its contact position by a member of the contact opening mechanism that is adapted to open the electrical circuit to be protected.
The invention aims to improve the above kind of differential switch provided with a test circuit, in particular with regard to the automatic breaking function.
To this end it proposes a differential switch including:
- a fixed power contact and a pivoting power
contact that has a closed position in which it is
disposed against the fixed contact and an open position
in which it is separated from the fixed contact, and
- a test switch,
characterised in that it further includes:
- a  conductive  automatic  breaking  branch
connected to one terminal of the test switch and
extending in a direction transverse to a pivot pin of the
pivoting contact, and
- a conductive automatic breaking blade connected
to said pivoting contact and disposed facing the
automatic breaking branch so that when the pivoting
contact is in the closed position the automatic breaking
blade is disposed against the automatic breaking branch
and when the pivoting contact is in the open position the
automatic breaking blade is separated from the automatic
breaking branch.
The components for implementing the automatic breaking function of a differential switch of the above kind are connected directly to the components for
implementing the function of opening the electrical circuit to be protected.
This is because, the automatic breaking blade being connected directly to the pivoting contact and the automatic breaking branch being disposed facing the automatic breaking blade, these components may be mounted directly on the mechanism of the differential switch. For example, it is not necessary for the? casing of the differential switch to support these components, which makes the mechanism independent of dimensional tolerances or variations in the shape of a component attached to the mechanism, such as the casing.
Moreover, disposing the conductive branch so that it; extends in a direction transverse to the pivot pin of the pivoting contact not only exploits the pivoting of the contact to provide the automatic breaking function but also exploits this pivoting in a manner that is virtually independent of the variation in the position of the pivot pin.
If the components constituting the mechanism of the differential switch tend to deform, for example as a result of creep or moisture, the pivot pin of the pivoting contact tends to move in a direction substantially parallel to the automatic breaking branch, which will have little effect on the contact between the automatic breaking blade and the automatic breaking branch, which depends essentially on the position of the automatic breaking blade relative to said pivot pin co which it is connected.
According to a preferred feature, the pivoting contact further includes a projecting distance member adapted to raise the automatic breaking branch when the pivoting contact is in the open position. The distance member may be an insulative material tongue disposed transversely to the automatic breaking branch.
This distance member increases the distance between the automatic breaking branch and the automatic breaking blade when the pivoting contact is in the open position, which improves the isolation between those two members and enhances the independence of the mechanism from fabrication tolerances and deformation of the differential switch.
To position the automatic breaking branch correctly, the distance member may include a notch adapted to guide the automatic breaking branch.
The distance member and the automatic breaking blade are preferably disposed face to face and on respective opposite sides of the pivot pin of the pivoting contact.
This allows the automatic breaking blade and the automatic breaking branch to co-operate with each other so that when the automatic breaking blade moves away from the automatic breaking branch the distance member raises the latter and when the automatic breaking blade approaches the automatic breaking branch the distance member releases it. Thus the effects of these two components are advantageously cumulative.
Moreover, the differential switch may further include a first stop finger disposed on the path of movement of the automatic breaking branch and adapted to limit the raising thereof. Similarly it may further include a second stop finger disposed facing the first stop finger and the automatic breaking branch may be held between the first stop finger and the second stop finger.
These fingers effectively retain the automatic breaking branch to ensure good electrical contact when the automatic breaking blade is placed against the automatic breaking branch.
According to a preferred feature, the test switch includes:
- a test pushbutton having a rest position and an
operated position, and
- a pusher spring connected to the automatic
breaking branch and disposed facing a conductive contact
member,
the pusher spring being operated by the test pushbutton so that when the test pushbutton is in the rest position the spring is separated from the contact member and when the test pushbutton is in the operated position the spring is in contact with the contact member.
The test switch is therefore economical and reliable.
The number of components in the test circuit may be significantly reduced if the pusher spring and the automatic breaking branch are made in one piece.
For reasons of convenience of manufacture, the pivoting contact may be mounted on an insulative material pivoting support including a projecting tongue forming the distance member. Similarly, the mobile contact may be connected to a conductive contact spring leaf which has a projecting portion forming the automatic breaking blade.
Other features and advantages of the invention will become apparent in the light of the following description of a preferred embodiment given by way of non-limiting example, which description refers to the appended drawings, in which:
- figure 1 is a perspective view of an assembly
including a toggle, a fixed contact, a mobile contact
carrying an automatic breaking blade and a component
forming a pusher spring and automatic breaking branch,
showing the mobile contact in a closed position;
- figure 2 is a side view corresponding to
figure 1;
- figure 3 is a view similar to figure 1, showing
the mobile contact in an open position;
- figure 4 is a side view corresponding to
figure 3; and
- figure 5 is a view corresponding to a view from
the left-hand side of figure 4 and including additional
components of the differential switch: a second pair of
contacts and a test pushbutton operating the contact
spring.
Figures 1 to 4 show certain of the components of the test circuit of a differential switch, shown in the positions that they normally occupy in the differential switch, although, for reasons of clarity, the remainder of the mechanism is not shown.
These figures show a fixed contact 1 and a mobile contact 2 adapted to open or close the electrical circuit to be protected under the control of the differential switch.
The operation of a differential switch being familiar to the person skilled in the art, it will not be described in detail here, and for the same reason the corresponding components are not shown. Suffice to say that the mobile contact 2 is operated to move it away from the fixed contact 1 (open position) in the event of an electrical fault.
An opening spring 3 spring-loads the contacts 1, 2 into their rest position, which is the open position.
The mobile contact 2 includes a contact member 4 adapted to be positioned against a similar contact member 5 that is part of the fixed contact 1 when the mobile contact 2 is in its closed position.
The contact member 4 of the mobile contact 2 is mounted in an insulative support 6 and locked by a contact spring leaf 7 also providing the automatic breaking blade function explained hereinafter.
The insulative support 6 is mounted so that it
can pivot about a pivot pin 8 to impart to the mobile contact the degree of freedom necessary to occupy its closed position (figures 1 and 2) and its open position (figures 3 and 4).
The insulative support 6 further includes a tongue 14 projecting in front of the contact spring leaf 7, the two components 7, 14 extending in a direction transverse to the pivot pin 8 on respective opposite sides of the pivot pin 8. The upper portion of the tongue 14 includes a notch 19 adapted to co-operate with an automatic breaking branch 10.
Figures 1 to 5 also show a toggle 9 adapted to be accessible from the outside so that the user can manipulate it. It operates the mechanism of the differential switch and has two positions corresponding to the two positions of the mobile contact 2 shown in figures 1 and 3.
A single component including an automatic breaking branch 10 and a pusher spring 11 is disposed on the mechanism so that the automatic breaking branch extends just above the insulative support 6 and transversely to the pivot pin 8.
The automatic breaking branch 10 is also held in position between two stop fingers 12, 13 attached to a fixed portion of the differential switch (not shown).
Moreover, the automatic breaking branch 10 is attached to a pusher spring 11 formed of a helicoidal winding and a projecting branch 15 disposed in front of a conductive contact member 16.
The conductive contact member 16 is adapted to be connected to one terminal of a test resistor (not shown) the other terminal of which is connected to one pole of the differential switch.
Referring to figure 5, a test pushbutton 17 cooperates with the projecting branch 15 and is adapted to
be retained by the casing (not shown) of the differential switch so that it is able to slide between a rest position in which it does not load the projecting branch 15 and an actuation position in which, when it is pressed by the user, it pushes the projecting branch against the contact member 16.
Figure 5 shows the same components as figures 1 to 4 and additionally a second pair of contacts 18 operated at the same time as the contacts 1, 2 described above, which is standard practice in a differential switch.
In the position shown in figures 1 and 2, the differential switch is set and the mobile contact 2 is in the closed position.
Accordingly, given the disposition of the tongue 14 and the automatic breaking blade 7, the tongue 14 is separated from the automatic breaking branch 10 and the automatic breaking blade 7 is positioned against the automatic breaking branch 10. The retention of the latter by the stop fingers 12, 13 exploits its elasticity to guarantee good electrical contact with the automatic breaking blade 7.
In figures 1 and 2, the projecting branch 15 is held against the conductive contact member 16, which corresponds to operation of the test pushbutton 17 by the user, although, for reasons of clarity, the pushbutton is not shown in these figures.
In this configuration, electrical continuity is assured between the fixed contact 1 (and therefore one of the poles of the differential switch) and the conductive contact member 16 (and thus another pole of the differential switch) via the test resistor.
The automatic breaking function is therefore not activated and pressing the test pushbutton 17 performs the test function.
In figures 3 and 4, on the other hand, the differential switch has been tripped and the mobile contact 2 is therefore in the open position.
The tongue 14 is then held against the automatic breaking branch 10 and raises it, whereas the automatic breaking blade 7 is separate from it.
The distance between the automatic breaking blade 7 and the automatic breaking branch 10 depends on the distance between the tongue 14 (and therefore the pivot pin 8) and the stop fingers 12, 13.
This activates the automatic breaking function, meaning that the electrical continuity of the test circuit is not established even if the test pushbutton 17 is pressed to make contact between the branch 15 and the contact member 16.
More generally, the invention is not limited to the examples described and shown, in particular with regard to the arrangement of the conductive contact member 16 and the pusher spring 11.

CLAIMS
1. Differential switch including:
- a fixed power contact (1) and a pivoting power
contact (2) that has a closed position in which it is
disposed against the fixed contact (1) and an open
position in which it is separated from the fixed contact
(1), and
- a test switch (15, 16, 17),
characterised in that it further includes:
- a conductive automatic breaking branch (10)
connected to one terminal of the test switch (15, 16, 17)
and extending in a direction transverse to a pivot pin
(8) of the pivoting contact (2), and
- a conductive automatic breaking blade (7)
connected to said pivoting contact (2) and disposed
facing the automatic breaking branch (10) so that when
the pivoting contact (2) is in the closed position the
automatic breaking blade (7) is disposed against the
automatic breaking branch (10) and when the pivoting
contact (2) is in the open position the automatic
breaking blade (7) is separated from the automatic
breaking branch (10).

2. Differential switch according to claim 1,
characterised in that the pivoting contact (2) further
includes a projecting distance member (14) adapted to
raise the automatic breaking branch (10) when the
pivoting contact (2) is in the open position.
3. Differential switch according to claim 2,
characterised in that the distance member (14) is an
insulative material tongue disposed transversely to the
automatic breaking branch (10).
4. Differential switch according to claim 3,
characterised in that the distance member (14) includes a
notch (19) adapted to guide the automatic breaking branch
(10) .
5. Differential switch according to any one of
claims 2 to 4, characterised in that the distance member
(I"l) and the automatic breaking blade (7) are disposed
face to face and on respective? opposite; sides of the
pivot pin (8). of the pivoting contact (2) .
6. Differential switch, according to any one of
claims 1 to S, characterised in that it further includes
a first stop finger (12) disposed on the path of movement:
of the automatic breaking branch (10) and f:u:lapted to
11 mi t t he r a i s :i rig t: h e r eo f .
7. Differential switch according to claim 6,
characterised in that it further- includes a second stop
finqer (13) disposed facing the first stop finger (12)
and the automatic breaking branch (10) is held between
the first stop finger (12) and the second stop finger
(13) .
8. Differentia], switch according to any one of
claims 1 to 7, characterised in that the test switch
includes:

- a test pushbutton (.1.7) having a rest position
and. an operation position, and
- a pusher spring (11, 35) connected to the
automatic breaking branch (10) and disposed facing a
conductive contact member (16),
the pusher spring (11, IB) being opereited by the test pushbutton (17) so that when the test pushbutton (17) is in the rest position the spring (11, 1B) is separated from the contact member (IS) and when the test pushbutton (17) is in the operated position the spring (11, lb) is in contact with the contact member (16).
9. Differential switch according to claim 8,
characterised in that: the pusher spring (11, 15) and the
automatic breaking branch (10) are made in one piece.
10. Differential switch according to ariv one of
claims 1 to 9, characterised in that, the pivoting contact
(2) is mounted on an insulative material pivoting support (6) including a projecting tongue (14) forming the
distance member.
11. Differential switch according to any one of
claims 1 to 10, characterised^ in that the mobile contact (2) is connected to a conductive contact spring leaf (7)
which has a projecting portion forming the automatic
breaking blade.