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Title:
A RESIDUAL CURRENT DEVICE MECHANISM AND MODULE
Document Type and Number:
WIPO Patent Application WO/2009/005374
Kind Code:
A1
Abstract:
A circuit-breaking mechanism for use in a residual current device (RCD) comprises a main shaft which defines an axis of rotation about which parts of the mechanism move pivotally. A modular RCD is disclosed having a casing with a length dimension which is greater than transverse dimensions of the casing, housing the circuit-breaking mechanism.

Inventors:
SCOTTORN DAVID (NZ)
SCOTTORN MARTIN (NZ)
Application Number:
PCT/NZ2008/000156
Publication Date:
January 08, 2009
Filing Date:
June 30, 2008
Export Citation:
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Assignee:
SCHNEIDER ELECTRIC NEW ZEALAND (NZ)
SCOTTORN DAVID (NZ)
SCOTTORN MARTIN (NZ)
International Classes:
H01H3/00; H02H3/00
Domestic Patent References:
WO2001097243A12001-12-20
WO2000060628A12000-10-12
Foreign References:
US4409574A1983-10-11
US20070030608A12007-02-08
US7136267B22006-11-14
US20050231861A12005-10-20
US6624991B22003-09-23
US20020154488A12002-10-24
US5933063A1999-08-03
US5517165A1996-05-14
GB2247354A1992-02-26
Attorney, Agent or Firm:
ADAMS, Matthew, D et al. (6th Floor Huddart Parker BuildingPO Box 949, Wellington 6015, NZ)
Download PDF:
Claims:

CLAIMS.

1 A circuit-breaking mechanism for use as part of a Residual Current Device (RCD) assembly, comprising; a main shaft which defines an axis of rotation, a first pair of fixed contacts, spaced from said axis of rotation, each of said first pair electrically separate from the other, a second pair of fixed contacts, spaced from said axis of rotation, each of said second pair electrically separate from the other, and said second pair electrically separate from said first pair, one of said first pair adapted for connection to live supply and one of said second pair adapted for connection to neutral supply, the others of said first and second pairs adapted for connection to live and neutral load respectively, a movable contact carrier, having a main body rotatably mounted onto said main shaft, said movable contact earner including a first contact bridge and a second contact bridge, said second contact bridge electrically independent of said first contact bridge, said movable contact carrier rotatable from an open position where said first and second contact bridges are spaced apart from said respective first and second contact pairs, to a closed position where said first contact bridge spans between each of said first contact pair to form a first current path, and said second contact bridge spans between each of said second contact pair to form a separate second current path, a user-activated latching assembly, adapted to releasably engage with said movable contact earner, a contact earner spnng biasing said movable contact earner towards said open position, and an opposed latch carrier spnng, arranged such that when said latching assembly is engaged with said movable contact carrier, said latch carrier spnng biases said movable contact carrier towards said closed position.

2. A circuit breaking mechanism as claimed in claim 1 wherein said latch carrier spnng has a greater force constant than said contact carrier spring so that said latch carrier spring overpowers said contact carrier spnng.

3. A circuit breaking mechanism as claimed in claim 1 or claim 2 wherein said latch carrier spnng and said contact carrier spnng are coiled torsion springs

4. A circuit breaking mechanism as claimed in any one of claims 1 — 3 wherein said latch carrier spring and said contact carrier spring are mounted about said main shaft

5. A circuit breaking mechanism as claimed in any one of claims 1 — 4 wherein said latching assembly comprises a latch carrier, having a main body rotatably mounted on said main shaft, and a latch having a first end and a second end and mounted on and movable with said latch earner to releasably engage with said movable contact earner.

6. A circuit breaking mechanism as claimed in claim 5 wherein said movable contact carrier includes a latch tongue extending from said contact earner main body to engage with said latch in use.

7. A circuit breaking mechanism as claimed in claim 6 wherein said latch tongue includes a recess, and said first end of said latch includes a notch for engaging widi said recess in the latch tongue.

8. A circuit breaking mechanism as claimed in claim 7 wherein said latch assembly includes a spring, biasing said first end of said latch towards said recess.

9. A circuit breaking mechanism as claimed in any one of claims 5 — 8 wherein said latch is mounted on said latch carrier such that said latch can pivot about a substantially central point, said pivoting motion occurring parallel to said axis of rotation, relative to said latch earner.

10. A circuit breaking mechanism as claimed in claim 9 wherein said pivoting motion of said latch is through a maximum of about 20 degrees.

11. A circuit breaking mechanism as claimed in any one of claims 5 — 10 wherein latch carrier includes a first projection and a second projection extending outwards from said latch carrier main body, said projections angled away from each other.

12. A circuit breaking mechanism as claimed in claim 11 wherein said latch carrier spring has a first end and a second end, said first end held in position, said second projection on said latch cairier acting on said second end so that said latch carrier spring is twisted as said latch carrier main body rotates.

13. A circuit breaking mechanism as claimed in any one of claims 1 — 12 wherein said first and second contact bridges are aligned substantially parallel to said axis of rotation

14. A circuit breaking mechanism as claimed in any one of claims 1 - 13 wherein said first and second contact pairs are aligned substantially parallel to said axis of rotation, said first contact pair at the same radial distance from said mam shaft as said first contact bridge, and said second contact pair at the same radial distance from said main shaft as said second contact bridge.

15. A circuit breaking mechanism as claimed in any one of claims 1 — 14 wherein said contact earner spring has a first end and a second end, said first end held in position, said movable contact carrier acting on said second end so that said contact earner spring is twisted as said movable contact earner rotates.

16. A circuit breaking mechanism as claimed in any one of claims 1 — 15 wherein said contact bndges compnse leaf spnngs, biasing said bridges outwards

17. A module for use with a power supply assembl ) , said module in use located in the current pathway between live supply and load, and neutral supply and load, compnsing; a solenoid assembly, sensing circuitry to sense a current imbalance between said live and neutral current paths and change an activation state of said solenoid assembly on sensing said unbalance, electrical supply contacts adapted for connection to live supply and neutral supply, electrical load contacts adapted for connection to live load and neutral load, a circuit-breaking mechanism, a casing, having transverse dimensions and a length dimension which is greater than said transverse dimensions, enclosing said circuit-breaking mechanism, said solenoid assembly and said sensing circuitr) and adapted to allow external electrical connections to be made to hve and neutral supply and load, a user-operated reset mechanism, said circuit-breaking mechanism comprising, a movable contact carrier carrying at least some of said electrical contacts and mounted for movement about an axis of rotation substantially aligned with said length dimension, and rotatable about said axis of rotation between a position where said contacts are open and current

cannot flow between load and supply, and a position where said contacts are closed allowing current to flow between load and supply, a contact carrier spring adapted to bias said movable contact carrier towards said open position, a latching assembly adapted to engage with and bias said movable contact carrier towards said closed position when said latching assembly and said movable contact carrier are engaged, said solenoid assembly adapted to disengage said latching assembly from said movable contact carrier when said activation state is changed, said reset mechanism being operable by a user to engage said latching assembly with said movable contact carrier, said latching assembly and said movable contact carrier remaining latched until a current imbalance is detected and said activation state changes.

18. A module as claimed in claim 17 wherein said circuit-breaking mechanism includes; a first pair of fixed contacts, spaced from said axis of rotation, each of said first pair electrically separate from the other, a second pair of fixed contacts, spaced from said axis of rotation, each of said second pair electrically separate from the other, and said second pair electrically separate from said first pair, said movable contact carrier including a first contact bridge and a second contact bridge, said second contact bridge electrically independent of said first contact, bridge, said movable contact carrier rotatable from said open position where said first and second contact bridges are spaced apart from said respective first and second contact pairs, to said closed position where said first contact bridge spans between each of said first contact pair to form a first current path, and said second contact bridge spans between each of said second contact pair to form a separate second current path.

19. A module as claimed in claim 17 or claim 18 wherein said solenoid assembly comprises a solenoid and a solenoid frame, said solenoid connected to said sensing circuitry, said solenoid and said solenoid frame arranged so that when said activation state changes, said solenoid frame moves from a neutral position to an unlatching position where said frame disengages said latching assembly from said movable contact carrier.

20. A module as claimed in claim 19 wherein said solenoid and solenoid frame are further arranged such that said frame returns to said neutral position when said solenoid is deactivated.

21. A module as claimed in any one of claim 19 or claim 20 wherein said sensing circuitry is arranged to activate said solenoid only on detection of a current imbalance between said live and neutral current paths.

22. A module as claimed in any one of claims 19 — 20 wherein said solenoid frame is biased towards said neutral position by a spring.

23. A module as claimed in any one of claims 19 — 22 wherein said latching assembly comprises a latch earner, having a main body rotatably mounted on said main shaft, a latch earner spring adapted to bias said latch carrier towards said closed position, and a latch having a first end and a second end, said latch mounted on and movable with said latch earner, said latch adapted to releasably engage widi said movable contact carrier.

24. A module as claimed in claim 23 wherein a first end of said latch carrier spring is located in a recess on the inner surface of said casing.

25. A module as claimed in any one of claim 23 or claim 24 wherein said latching assembly has a main body that includes a first projection and a second projection, said reset mechanism acting on said second projection as it is operated by a user, and causing said latch earner to rotate.

26. A module as claimed in claim 25 wherein said reset mechanism is a reset button which is rotatable inwards about its top edge to act on said second projection.

27. A module as claimed in any one of claims 23 - 26 wherein said solenoid frame is aligned in said casing to act on said second end of said latch when said solenoid is activated, said frame rotating said latch so that said first end disengages from said movable contact carrier.

28. A module as claimed in any one of claims 17 - 27 wherein said module also includes a test button, connected to a test wire, activation of said test button causing at least some of said current between load and supply to flow along said test wire, creating a current imbalance.

29. A module as claimed in any one of claims 17 - 28 wherein a first end of said contact carrier spring is located in a recess on the inner surface of said casing.

30. A module as claimed in any one of claims 17 — 29 wherein said sensing circuitry is arranged to change the activation state of said solenoid assembly on detection of a current imbalance between said live and neutral current paths, or a drop in the voltage level.

31. A module as claimed in any one of claims 17 — 30 wherein said module is sized so that it can be used in a standard module aperture in a standard grid component of an electrical fitting.

32. A module for use with a power supply assembly, said module in use located in the current pathway between live supply and load, and neutral supply and load, comprising; a solenoid assembly, sensing circuitry, adapted to sense a current imbalance between said live and neutral current paths and change an activation state of said solenoid assembly on sensing said imbalance, electrical supply contacts adapted for connection to live supply and neutral supply, electrical load contacts adapted for connection to live load and neutral load, a circuit-breaking mechanism, a casing, having transverse dimensions and a length dimension which is greater than said transverse dimensions, enclosing said circuit-breaking mechanism, said solenoid assembly and said sensing circuitry and adapted to allow external electrical connections to be made to live and neutral supply and load, said circuit-breaking mechanism comprising; a mam shaft which defines an axis of rotation, substantially aligned with said length dimension

33. A module for use with a power supply assembly, said module in use located in the current pathway between live supply and load, and neutral supply and load, comprising, a solenoid assembly, sensing circuitry, adapted to sense a current imbalance between said live and neutial current paths and change an activation state of said solenoid assembly on sensing said imbalance, electrical suppl ) contacts adapted for connection to live supply and neutral supply, electrical load contacts adapted for connection to live load and neutral load, a circuit-breaking mechanism, a casing, having transverse dimensions and a length dimension which is greater than said tiansverse dimensions, enclosing said circuit-breaking mechanism, said solenoid assembly and said sensing circuitry and adapted to allow external electrical connections to be made to live and neutral suppl } and load,

a user-operated reset mechanism, said circuit-breaking mechanism comprising; a main shaft which defines an axis of rotation, substantially aligned with said length dimension, a movable contact earner, mounted on said main shaft and adapted to carry at least some of said electrical contacts, and rotatable about said axis of rotation between a position where said contacts are open and current cannot flow between load and supply, and a position where said contacts are closed allowing current to flow between load and supply, said solenoid assembly adapted to move said movable contact carrier from said position where contacts are closed to said position where contacts are open when said activation state is changed, in use, said reset mechanism operated by a user moves said mo\ able contact carrier into said position where contacts are closed, said movable contact carrier remaining in said position where contacts are closed until a current imbalance is detected and said activation state changes.

34. A module as claimed in any one of claims 17 to 33 wherein the sensing circuitry comprises: a sensor circuit having the live and neutral current paths connected to its input, and an analogue to digital converter having an input connected to the output of the sensor circuit, and a microcontroller having an input connected to the output of the analogue to digital converter, and a tripping device connected to an output of the microcontroller.

35. A module as claimed in claim 34 wherein a threshold value is stored in the microcontroller, the threshold value being indicative of the minimum output value of the analogue to digital converter required to change said activation state

36 A module as claimed in either of claims 34 oi 35 wherein the microcontroller is calibratable by passing a fault current through the input of the sensor circuit and computing the difference between the input of the microcontroller as a result of the fault current to an expected input value and stoiing two thieshold values in the internal memory of the microcontroller based on this input.

37. A module as in claim 36 wherein the input of the microcontroller in normal operation is compared against the two stored threshold values to indicate a change in activation state.

38. A module as claimed in any one of claims 34 to 38 wherein the sensing circuitry is arranged to perform a periodic self-test to check sensor circuit functionality.

39. A module as claimed in any one of claims 34 to 39 wherein the sensing circuitry is arranged to monitor zero crossing and peak state of AC mains connected to the circuitry.

40. A module as claimed in any one of claims 34 to 40 arranged to provide a visual warning on incorrect wiring of the module in circuit.

41. A module as claimed in any one of claims 34 to 41 wherein the sensing circuitry is arranged to monitor the AC mains waveform connected to the circuitry to detect disturbances caused by arcing and change the activation state to activate the tripping circuit on detection of such disturbances.

42. A module as claimed in any one of claims 34 to 41 wherein the sensing circuitry is arranged to change the activation state on overheating.

Description:

"A RESIDUAL CURRENT DEVICE MECHANISM AND MODULE"

FIELD OF INVENTION

This invention relates to residual current devices (RCD's), also known as residual current circuit breakers (RCCB's), ground fault circuit interrupters (GFCFs) or appliance leakage current interrupters (ALCFs).

BACKGROUND OF THE INVENTION

An RCD is an electrical wiring device that disconnects a circuit whenever it detects that die flow of current is not balanced between the live conductor and the neutral conductor. If the current flow is not balanced, this may be because current is leaking from the circuit to earth. If this leakage to earth occurs through the body of a person who is accidentally touching the energized part of the circuit, a shock is likely to result. RCD's are therefore commonly placed in electrical circuits where there is a high risk of a leak occurring. For example, they are commonly placed in bathrooms where electrical devices are used (electric razors, hairdryers, etc), where there is a danger of these devices being accidentally dropped and becoming submerged. RCD's are also commonly used in or with mains powered, hand-operated cutting tools (e.g. lawnmowers) where there is a possibility that the power cord could be accidentally severed or partially cut, exposing the live wire The mechanism of one form of typical RCD is shown in Figure 1. The RCD depicted is designed to be wired in-line with an appliance flex of a type typically rated to carry a maximum current of 13 amperes, and to trip on a leakage current of 30 mA. The incoming live current supply and the grounded neutral conductors are connected to live terminals 101a and 101b respectively, and the outgoing load conductors (live and neutral) are connected to outgoing terminals 102a and 102b respectively The earth conductor (not shown) is connected through from supply to load uninterrupted.

When reset button 103 is pressed, contacts 104 close, allowing current to pass. Solenoid 105 keeps the contacts closed when the reset button is released.

The sensing coil 106 is a differential current transformer which surrounds the live and neutral conductors. In normal operation, all the current flowing in the live conductor returns via the neutral conductor and the current magnitudes are therefore equal and opposite and cancel each other within coil 106

Any fault to earth during operation causes some current to take a different return path, creating an imbalance or difference in the current flow The imbalance causes a current to flow in the sensing coil 106, which is detected by sensing circuitry 107, which then removes power

from the solenoid 105, activating the mechanism so that the contacts 104 are forced apart by a spring, cutting off power to the appliance Test button 108 allows the correct operation of the device to be verified by passing a small current through the test wire 109 This simulates a fault by creating an imbalance in the sensing coil, which should cause the device to trip RCD's are also commonly hard-wired into an electrical system - e g a domestic electrical system Typically, an RCD may be integrally formed as part of an electrical socket assembly installed in a kitchen or bathroom An example of a socket which includes an integrated RCD 203 is shown in Figure 3

One form of (non-RCD protected) socket assembly is shown in Figure 2 It and the socket assembly of Figure 3 include a face plate 200, a switch unit 201 formed as a module which is inserted into a grid component (not shown) behind the face plate and a socket unit 202 The modular switch unit 201 can be used with either a single switched socket as shown or double switched socket or other electrical fittings

SUMMARY OF THE INVENTION

In a first aspect, die present invention may broadly be said to consist in a circuit breaking mechanism for use as part of an RCD assembly, comprising, a main shaft which defines an axis of rotation, a first pair of fixed contacts, spaced from said axis of rotation, each of said first pair electrically separate from the other, a second pair of fixed contacts, spaced from said axis of rotation, each of said second pair electrically separate from the other, and said second pair electrically separate from said first pair, one of said first pair adapted for connection to live supply and one of said second pair adapted for connection to neutral supply, the others of said first and second pairs adapted for connection to live and neutral load respectively, a movable contact carrier, having a main body rotatably mounted onto said main shaft, said movable contact carrier including a first contact bridge and a second contact bndge, said second contact bridge electrically independent of said first contact budge, said movable contact carrier rotatable from an open position where said first and second contact bridges are spaced apart from said respective first and second contact pairs, to a closed position wheie said first contact budge spans between each of said first contact pair to form a fiist current path, and said second contact bridge spans between each of said second contact pair to foim a separate second current path,

a user-activated latching assembly, adapted to releasably engage with said movable contact earner, a contact carrier spring biasing said movable contact carrier towards said open position, and an opposed latch carrier spring, arranged such that when said latching assembly is engaged with said movable contact carrier, said latch carrier spring biases said movable contact earner towards said closed position

Preferably said latch carrier spring has a greater force constant than said contact earner spring so diat said latch carrier spring overpowers said contact carrier spring.

Preferably said latch carrier spring and said contact carrier spring are coiled torsion springs.

Preferably said latch carrier spring and said contact earner spring are mounted about said main shaft.

Preferably said latching assembly comprises a latch carrier, having a main body rotatably mounted on said main shaft, and a latch having a first end and a second end, said latch mounted on and movable with said latch carrier, said latch adapted to releasably engage with said movable contact earner

Preferably said movable contact earner includes a latch tongue, extending from said contact earner main body and adapted to engage with said latch in use.

Preferabl) said first and second contact bridges are aligned substantially parallel to said axis of rotation when said movable contact carrier main body is threaded onto said main shaft.

Preferably each of said first and second contact pairs are aligned substantially parallel to said axis of rotation, said first contact pair at the same radial distance from said main shaft as said first contact bπdge, and said second contact pair at the same radial distance from said main shaft as said second contact bridge. Preferably said latch is mounted on said latch earner such that said latch can pivot about a substantially central point, said pivoting motion occurring parallel to said axis of rotation, relative to said latch earner

Preferably the range of said latch parallel rotation is a maximum of about 20 degrees.

Preferably said latch tongue includes a recess, and said first end of said latch includes a notch, said notch engaging with said recess in use

Preferably said latch assembl) includes a spring, biasing said first end of said latch towards said recess

Preferably said latch carrier includes a first projection and a second projection extending outwards ftom said latch earner mam body, said projections angled away from each other.

- A -

Preferably said latch carrier spring has a first end and a second end, said first end held in position in use, said second projection on said latch carrier acting on said second end so that said latch earner spring is twisted as said latch earner main body rotates.

Preferably said contact earner spring has a first end and a second end, said first end held in position in use, said movable contact carrier acting on said second end so that said contact carrier spring is twisted as said movable contact earner rotates

Preferably said contact bndges include or comprise leaf springs, biasing said bridges outwards. In a second aspect, the invention may broadly be said to consist in a module for use with a power supply assembly, said module in use located in the current pathway between live supply and load, and neutral supply and load, compnsing; a solenoid assembly, sensing circuitry, adapted to sense a current imbalance between said live and neutral current paths and change an activation state of said solenoid assembly on sensing said imbalance, electncal supply contacts adapted for connection to live supply and neutral supply, electrical load contacts adapted for connection to live load and neutral load, a circuit-breaking mechanism, a casing, having transverse dimensions and a length dimension which is greater than said transverse dimensions, enclosing said circuit-breaking mechanism, said solenoid assembly and said sensing circuitry and adapted to allow external electncal connections to be made to live and neutral supply and load, a user-operated reset mechanism, said circuit-breaking mechanism compnsing; a main shaft which defines an axis of rotation, substantially aligned with said length dimension, a movable contact carrier, mounted on said main shaft and adapted to carry at least some of said electncal contacts, and rotatable about said axis of rotation between a position where said contacts are open and current cannot flow between load and supply, and a position where said contacts are closed allowing current to flow between load and supply, a contact earner spring adapted to bias said movable contact carrier towards said open position, a latching assembly adapted to engage with and bias said movable contact carrier towards said closed position when said latching assembly and said movable contact carrier are engaged,

said solenoid assembly adapted to disengage said latching assembly from said movable contact earner when said activation state is changed, in use, said reset mechanism operated by a user to engage said latching assembly with said movable contact carrier, said latching assembly and said movable contact earner remaining latched until a current imbalance is detected and said activation state changes.

Preferably said circuit-breaking mechanism includes; a first pair of fixed contacts, spaced from said axis of rotation, each of said first pair electrically separate from the other, a second pair of fixed contacts, spaced from said axis of rotation, each of said second pair electrically separate from the other, and said second pair electrically separate from said first pair, said movable contact earner including a first contact bridge and a second contact bridge, said second contact bndge electrically independent of said first contact bridge, said movable contact earner rotatable from said open position where said first and second contact bndges are spaced apart from said respective first and second contact pairs, to said closed position where said first contact bndge spans between each of said first contact parr to form a first current path, and said second contact bridge spans between each of said second contact pair to form a separate second current path. Preferably said solenoid assembly comprises a solenoid and a solenoid frame, said solenoid connected to said sensing circuitry, said solenoid and said solenoid frame adapted so that when said activation state changes, said solenoid frame moves from a neutral position to an unlatching position where said frame disengages said latching assembly from said movable contact earner. Preferably said solenoid and solenoid frame are further adapted such that said frame returns to said neutral position when said solenoid is deactivated

Preferably said solenoid frame is biased towards said neutral position by a spring. Preferably said module also includes a test button, connected to a test wire, activation of said test button causing at least some of said current between load and supply to flow along said test wire, creating a current imbalance.

Preferably said latching assembly comprises a latch carrier, having a mam body rotatably mounted on said mam shaft, a latch spring adapted to bias said latch carrier towards said closed position, and a latch having a first end and a second end, said latch mounted on and movable with said latch carrier, said latch adapted to releasably engage with said movable contact carrier.

Preferably said solenoid frame is aligned in said casing to act on said second end of said latch when said solenoid is activated, said frame rotating said latch so that said first end disengages from said movable contact earner

Preferably said latching assembly has a main body that includes a first projection and a second projection, said reset button acting on said second pro j ection as it is operated by a user, and causing said latch earner to rotate

Preferably said first end of said latch carrier spnng is located in a recess on the inner surface of said casing Preferably said first end of said contact carrier spnng is located in a recess on the inner surface of said casing

Preferably said sensing circuitry is adapted to change the activation state of said solenoid assembly on detection of a current imbalance between said live and neutral current paths, or a drop in the voltage level Alternatively said sensing circuitry is adapted to activate said solenoid only on detection of a current imbalance between said live and neutral current paths

Preferably said reset button is adapted to rotate inwards about its top edge to act on said second projection

Preferably said module is sized so that it can be used in a standard module aperture in a standard grid component of an electrical fitting

Preferably said module is sized so that it can be used as a component in a PDL 500 or PDL 600 series device

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred forms of the invention are described by wa j of example, with ieference to the accompanying drawings in which,

Figure 1 shows the mechanism of an RCD of a type well known in the ait Figure 2 shows a prior art modular single switched socket assembl) Figure 3 shows an example of a socket which includes an integrated RCD

Figufe 4 shows a perspective view of an RCD module, comprising a casing containing the rotary RCD mechanism of the invention and associated elements, ready for fitting as part of a modular socket assembly.

Figure 5 shows interior detail of the RCD module of Figure 4 with the casing shown as a transparent outline, the rotary RCD mechanism shown at the front of the casing in an open or unlatched state, and a sensing coil, a solenoid assembly and a circuit board shown in position behind the rotary RCD.

Figure 6 shows a front view of the rotary RCD module of Figure 5 with the casing shown in transparent outline.. Figure 7 shows a perspective view from the left and above of the rotary RCD mechanism of the present invention, unlatched.

Figure 8 shows a perspective view from the right and above of the rotary RCD mechanism of the present invention, unlatched.

Figure 9 shows a perspective view from the left and underneath of the rotary RCD mechanism of the present invention, unlatched.

Figure 10 shows a view from underneath of the rotary RCD mechanism of the present invention, unlatched.

Figure 11 shows a perspective view from the right and underneath of the rotary RCD mechanism of the present invention, unlatched. Figures 12a, 12b and 12c show perspective cutaway views of the front portion of the RCD module of Figures 4 and 5, from underneath, with the front portion of the casing shown as a transparent outline, and the RCD mechanism shown unlatched.

Figure 13a and 13b show perspective cutaway views of the front portion of the RCD module, from underneath, with the reset button depressed so as to latch the RCD mechanism. Figures 14a and 14b show perspective views cutaway views of the front portion of the RCD module, from underneath, with the reset button released, and the RCD mechanism latched.

Figure 15 shows a front view of the RCD module of Figure 4, with the face plate shown as a transparent outline, and the RCD mechanism latched.

Figures 16a and 16b show perspective views of the front portion of the RCD module from underneath with the front portion of the casing shown in outline and the operation of the test button shown, with the solenoid shown tripping the latch.

Figure 17 shows a perspective view of an alternative form of RCD module with a different shaped casing, similar to the view of Figure 4 of the RCD module previously described.

Figure 18 is a perspective view of the RCD module of Figure 17 fitted to the grid component of an electrical fitting, showing a portion of the front face of the electrical fitting.

Figure 19 shows a preferred form of the circuit board circuitry.

Figure 20 shows a preferred functional flow chart of the microcontroller shown in the Figure 10 circuitry

- SI - DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the preferred embodiment, the RCD 1 is enclosed in a casing 100 having a standard modular size, the same as that of the switch unit module 201 in Figure 2 for example so that the RCD module may be fitted into, for example, the grid component of an electrical socket, in a module space which may alternatively accommodate components which provide other functions but which are of the same modular size. 'RCD module' is used to refer to the casing 100 and its contents, which include the rotary RCD mechanism 1 and other components required for the operation of the RCD module — e.g. a solenoid assembly 500. These components and their operation will be described in greater detail below. The width and height of the module are similar and the depth of the module is greater dian either its width or height, so that the complete RCD module has a shape as shown in Figure 4 and Figure 5. The RCD module can therefore be fitted into a standard module aperture in a standard grid component of an electrical fitting such as an electrical socket, to provide RCD functionality. The RCD module provides a current pathway between live supply and live load, and neutral supply and neutral load The RCD mechanism 1 , enclosed in casing 100, is shown in Figure 4. In use, the front face 103 of the casing 100 locates in a standard module aperture in the grid and faceplate of a socket assembl} , with the front face 103 flush with the faceplate.

Figure 5 shows interior detail of the RCD module. The casing 100 is shown as a transparent oudine. Figure 6 shows a front view of the RCD module, with the casing 100 and the front face 103 shown as a transparent outline, and the RCD mechanism 1 in an unlatched position A solenoid assembly 500, a sensing coil 300 and a circuit board 400 are located behind the RCD 1 , inside the casing 100.

The contacts mechanism of the preferred embodiment of the RCD 1 is shown from different angles in Figures 7 — 11 The contacts mechanism of the RCD 1 is assembled from the following main components: A main shaft 5; a latch earner 9; a latch carrier spring 10, a latch 12, a movable contact earner 6; a contact carrier spring 11 ; and two pairs of fixed contacts 14a and 14b, and 16a and 16b. The construction and operation of these main components, and other associated secondary components, is described below.

Main Shaft

In the preferred embodiment, the RCD 1 is mounted directly behind the faceplate 103 in the casing 100 The main shaft 5 is oriented to run from the front to the back of the RCD 1, perpendiculai to the faceplate 103, forming a main axis of rotation. A user operable reset button is located on the faceplate 103 of the casing 100

Latch Carrier

The latch carrier 9 is threaded onto the main shaft 5. That is, the latch earner 9 is mounted rotatably on the main shaft 5 A pair of projecting portions or projections 9a and 9b extend outwardly from the main body of the latch carrier 9, the pro j ections 9a and 9b extending outwards from the main body. Projection 9b is located in front of projection 9a. Viewed from the front, the two pro j ections extend outwards from the main body so that they appear angled at approximately 160-170° from each other. The latch carrier 9 in Figures 7 - 11 is shown in an open or initial position.

Latch Carrier Spring

A latch carrier spring 10 is connected to, and positioned on, the RCD 1 so that as the latch carrier 9 rotates, the latch carrier spring 10 becomes tensioned. In the preferred embodiment, the latch carrier spring 10 is a coiled torsion spring, and the coil of the spring 10 is twisted in use to place it in rotational tension The spring 10 is positioned on the main shaft 5 during assembly of the RCD 1. End 10a of the spring 10 is held in position, located behind a rib on the inner surface of the module case 100. This ensures that the end 1 Oa is held in position and does not rotate. End 10b of the spring 10 is co-located with the pro j ection 9b, so that as the latch carrier 9 moves and rotates, projection 9b acts on the end 10b, causing the spring 10 to be twisted, and tensioning it. It is preferred that the spring 10 is held slightly in tension when the RCD 1 is assembled, so that end 10b exerts a small force on the pro j ection 9b, holding the latch carrier 9 in the initial or first position Projection 9a also includes a recess to hold the latch 12 in position, as described below.

Latch In the preferred embodiment, the latch 12 is a spring-loaded latch, held in place by, and on, the latch carrier 9. As the latch carrier 9 rotates, the latch 12 moves with the latch carrier 9, describing an arc about the main rotation axis defined by the main shaft 5 The latch 12 has two ends, a first end and a second end 39, and a latch projection 37 located approximately midway between the two ends The latch projection 37 is slotted into a recess in piojection 9a, so that the latch 12 is held in position on the latch carrier 9. The fust end of the latch 12 includes a hook or notch 25 The latch 12 and the latch carrier 9 are connected such that the notched end 25 and the second end 39 can move or rotate about latch projection 37 through a very limited range of movement lelative to the latch carriei 9 — approximately 15 degrees, and only effectively parallel to the axis of rotation defined by main shaft 5. Effectively, the latch 12 pivots about the latch pro j ection 37

In the preferred embodiment, the latch carrier 9, the latch spring ??, and latch 12 form a latching assembly, although 'latching assembly' as it is used in this specification can refer to the assembly with our without the spring.

Movable Contact Carrier

In the preferred embodiment the movable contact carrier 6 comprises three flat parts 601, 602, 603 arranged at an angle, and spaced apart. The panels are connected to one another at each end by a pair of flanges 6a and 6b. Each flange 6a and 6b includes a central aperture through which passes main shaft 5, by which the movable contact earner 6 rotatably mounted to the main shaft 5. When viewed from the front of the RCD 1, panels 601 and 602 are the first two panels clockwise from the left, with panel 603 on the far right. Panels 601, 602 are aligned extending generally radially outwards from the rotation axis, and panel 603 is inclined so that it is approximately parallel to the preceding panel, panel 602, with each subsequent panel (602, then 603) spaced from the preceding panel at an interval of approximately 90 degrees. Panel 601 includes a contact area or bridge formed by a pair of electrical contacts or movable contacts 701, 702. Panel 602 includes a separate contact area or live bridge formed by a pair of electrical contacts 703, 704 Each of these pairs (pair 701, 702, and pair 703, 704) are arranged longitudinally, in a plane parallel to the rotation axis. Each half of each pair is in electrical contact with the other half to form the electrical bπdge. That is, contact 701 is permanendy electrically connected to contact 702, and contact 703 is permanently electrically connected to contact 704. Although in the preferred embodiment, the contact bridge on panel 601 is a pair of contact patches 701, 702, it could be formed as a continuous contact portion in alternative embodiments Similarl) the contact bπdge on panel 602 is formed from contacts 703, 704. Panel 603 also includes a latch tongue 20, which extends outwards perpendicularly from the clockwise face of the panel 603 (when viewed from the front). That is, the plane of die tongue 20 is parallel to the rotation plane. The tongue is located approximately halfway along the length of the panel 603. The latch tongue 20 includes an aperture 36 in approximately the centre of the latch tongue 20.

Contact Carrier Spring

The contact carrier spring 11 is similar to the latch carrier spring 10. It is a coiled torsion spring several times weaker than the latch carrier spring 10. The contact carrier spring 11 is arranged around the central rotation axis of main shaft 5, behind the latch carrier spring 10. In the preferred embodiment, one end l ib extends outwards from the main body of the spring 11

along the lower or clockwise face of the panel 603. The other end 11a is held in position so that, the contact earner spring 11 biases the movable contact carrier 6 towards an open position

Fixed Contacts The two pairs of fixed contacts 14a and 14b, and 16a and 16b are flat panels arranged in parallel to the axis of rotation and the panels 601, 602, 603. The fixed contacts 14 and 16 extend backwards from the front of the RCD 1, and are fixed in position (relative to the latch earner 9, latch 12, movable contact earner 6 and the main shaft 5). The ends 21, 22, 23, 24 of each one of these fixed contacts are at the rear of the RCD 1. The ends 21-24 of each of the fixed contacts are adapted for electncal connection to a mains circuit. In the preferred embodiment, these connections are made as follows: End 21 (on contact 14a) and end 22 (on contact 16a) are connected one to each of the live supply and load. End 23 (on contact 14b) and end 24 (on contact 16b) are connected one to each of the supply and load neutral. The pair of fixed contacts 14a and 14b includes a pair of electncal contact areas 30 and 32, one on each of the fixed contacts 14a and 14b. These are located towards the front of the fixed contacts. Similarly, the pair of fixed contacts 16a and 16b include a pair of electrical contact areas 31 and 33, located towards the rear of the fixed contacts. It is preferred that these contact areas are raised slighdy from the surrounding portions of the contacts to allow electncal contact to be achieved more effectively. In die preferred embodiment, the fixed contacts 14 and 16 are arranged so that contact areas 31 and 32 lie in the same plane as each other and are aligned along the rotation axis, and contact areas 30 and 33 lie in the same plane as each other and are aligned along the rotation axis. Also, that the contact areas 31 and 32 are arranged the same radial distance from the axis of rotation as the contacts 701 and 702, and the contact areas 30 and 33 are arranged the same radial distance from the axis of rotation as contacts 703 and 704. Each half of each pair is electrically separate or electncally isolated from the other half of the pair (that is, no current can flow between the two halves of the pair until a further electncal connection between the two halves is established - i.e. no current flows between contact areas 31 and 32, or between 30 and 33 unless a further connection is established). The two pairs are also electncally separate or electrically isolated from each other That is pair 31 and 32 are electrically separate from pair 30 and 33.

Operation

I he associated components and the operation of the RCD 1 will now be described with particular reference to Figures 12 to 15. The RCD 1 is shown located in the casing 100, unlatched, in Figuies 12a, 12b and 12c In operation, a user pushes the reset button 34 to

activate the RCD module. For example, if the RCD module is part of an electrical socket assembly, a user presses the reset button 34 to make the socket live. As shown in Figures 13a and 13b, as the reset button 34 is pressed, it acts on the latch carrier 9, which rotates, taking the latch 12 with it, the latch carrier 9 also acting on and tensioning the latch carrier spring 10 as described above (it can be seen that the latch carrier 9 is user-activated, via the reset button 34). From its initial position, the latch carrier 9 rotates through an arc of approximately 20 degrees. At the end of this arc, the latch 12 engages with the latch tongue 20 on the movable contact earner 6 as follows: As the latch 12 begins to move through its arc, it contacts the leading edge of the latch tongue 20. The end of the latch 12 - the hook 25 - is bias cut (cut at an angle), so that as the latch 12 continues to move through its arc of travel, some of the force on the end of the latch 12 will be converted to a sideways component, forcing the hook 25 sideways and rotating the latch 12 slightly sideways (perpendicular to the direction of travel of the latch 12 as it rotates). This rotation allows the latch 12 to move sufficiently so that it can pass along one side of the latch tongue 20. As the end of the latch 12 is bias cut, the latch 12 will always rotate in the same direction, and the latch 12 will always pass along the same face of the latch tongue 20. In the preferred embodiment, a latch spring 40 is connected between the latch 12 and the latch earner 9. The sideways rotation of the latch 12 compresses the latch spring 40. However, the body of the latch 12 could be formed from a resilient plastic, sized and shaped to allow the latch 12 to elastically bend or deform shghdy, achieving the same effect. At the end of the travel arc, the notch 25 moves beyond the far edge or trailing edge of the latch tongue 20. In this position, the latch 12 can rotate back towards its initial start plane. The compressed latch spnng 40 causes this rotation of the latch 12 back to its initial position. The notch 25 engages in the recess 36 on the latch tongue 20, engaging the latch 12 with the movable contact earner 6. The latch 12 can be disengaged from the movable contact earner by removing the notch 25 from the recess 36. That is, the latch 12 is releasably engaged with the movable contact earner 6.

As shown in Figures 14a and 14b, when the user releases the reset button, the latch earner spring 10, which has been rotationally compressed as the reset button was pressed, rotates the latch earner 9 clockwise, returning the latch earner 9 to a point close to its initial position. As described above, the latch 12 is connected to the latch carrier 9 and so the latch 12 also rotates clockwise back to close to its initial position. As the latch 12 and the movable contact carrier 6 are now engaged, the movable contact earner 6 also rotates clockwise around the central axis, moving with the latch carrier 9. It is preferred that this clockwise rotation of the latch carrier 9 and movable contact carrier 6 also pushes the reset button 34 back out (the reset button may also include a small bias spnng). The latch carrier spring 10 biases the movable

contact carrier 6 towards the closed position when the latching assembly is engaged with the movable contact carrier 6.

As described above, one end l ib of the contact carrier spring 11 extends along the lower or clockwise face of the panel 603 on the contact carrier 6. In the preferred embodiment, the latch carrier spring 10 is approximately three times stronger than the contact carrier spring 11, so the spring forces are unbalanced. Therefore, as the contact carrier 6 rotates clockwise, the latch carrier spring 10 overpowers the contact carrier spring 11, and the panel 603 acts on the end l ib of the contact carrier spring 11 , twisting and tensioning the contact earner spring 11 as the movable contact carrier 6 rotates clockwise with the latch carrier 9, back to a position close to the initial position of the latch carrier 9. The latch earner 9 will not return completely to its initial position, for reasons explained in detail below. As described above, the contact carrier 6 includes independent electncal contact bridges on the panels 601 and 602. As descnbed, each of these contact bridges are arranged on die movable contact carrier 6 longitudinally in a plane parallel to the rotation axis. As the contact earner 6 is rotated clockwise around the central axis, the contact bndge on panel 601 rotates clockwise and is pressed against the fixed contact areas 31 and 32. Similarly, the contact bndge on panel 602 rotates clockwise and is pressed against the contact areas 30 and 33. An electrical pathway or current path is therefore created between contact areas 31 and 32, and an independent electncal pathway or current path is created between the contact areas 30 and 33. Therefore, an electrical connection is made between ends 21 and 22, and a separate electncal connection is simultaneously made between ends 23 and 24. In this manner, a connection is made between live supply and live load, forming a current path between live supply and live load. A separate connection between neutral supply and neutral load is made, forming a current path between neutral supply and neutral load. The RCD 1 is now latched, or 'live'. A front view of the RCD module, with the front face 103 shown as a transparent outline, and the RCD 1 in the latched or live position, is shown in Figure 15.

In the preferred embodiment, a leaf spnng 8a is located behind contacts 701 & 702 to assist in pressing these into position and forming a good contact. The leaf spring 8a runs longitudinally along the panel 601. A similar leaf spring 8b is located running along the panel 602. The leaf springs 8a and 8b are placed slighdy in compression as the latch 12 locks into position, and serve to press the contacts 701, 702, 703, 704 against the contacts 31, 32, 33, and 30 respectively. The leaf springs 8a and 8b provide contact pressure and take up any relative positional difference between two fixed contacts. Because of the pressure exerted by these leaf springs 8a and 8b, the latch carrier 9 will not return completely to its initial position. The leaf springs are biased outwards - that is, away from their mounting points and towards the contacts.

As can be seen from the above, once the reset button 34 is pressed, electrical connections are made within the RCD 1 that allow the assembly of which it is a part to be used as normal. For example, if it is assembled into an electrical socket, once the RCD 1 is latched and is live, electrical appliances can be plugged into the socket and operated as normal. If an abnormal load is detected, the RCD 1 trips and the electrical contacts are broken as described below.

Tripping In order to break the electrical contacts, it is necessary to unlatch the latch 12. Once the latch 12 is unlatched, the contact carrier 6 is no longer engaged with the latch earner 9. The movable contact carrier 6 is therefore free to rotate, and the contact carrier spring 11 rotates it anticlockwise back to its start position. The latch carrier 9 and the latch 12 will also rotate clockwise fully back to their initial position (s), and the reset button will be held in the 'out' position.

The solenoid assembl} 500 shown in Figure 5 includes a solenoid frame 502. The front end of the solenoid frame 502 is located directly behind second end 39 of the latch 12 when the RCD 1 is latched. The frame 502 is held in a neutral position, towards the rear of the casing 100, by a connected spring 503. The latch 12 is unlatched as follows: In a similar fashion to RCD's of the prior art, the sensing coil 300 detects a non-zero current sum, and sensing circuitry located on the board 400 activates the solenoid 501, causing the solenoid frame 502 to move towards the front face 103. As the frame 502 moves towards the front face 103, it contacts second end 39 and moves it forwards towards face 103. This causes the latch 12 to pivot around the latch projection 37, so that the hook 25 moves backwards away from the face 103 and disengages from, or releases from engagement with, aperture 36. The movable contact carrier 6 is no longer held in position by the latch 12, and rotates anticlockwise under the force of the contact carrier spring 11. This breaks the electrical contact.

When the frame 502 moves forwards, this compresses the spring 503. With the solenoid frame 502 in the forward position, the latch 12 cannot be reengaged. The spring 503 returns to a neutral position, returning the solenoid frame 502 to the rear position, when the solenoid 501 is disengaged. However, to re-engage the live and neutral contacts in the RCD 1, a user must press the reset button 34.

As shown in Figures 16a and 16b, the mechanism of the RCD 1 can be tested by depressing the test button 35. When the test button 35 is depressed, test circuitry on the board

400 causes the current to unbalance slightly, activating the solenoid 501 and causing the solenoid frame 502 to move forward. This unlatches the latch 12 and allows the movable contact earner 6 to rotate anticlockwise, breaking the contacts and 'tripping' the rotary RCD 1.

Other

An RCD as described can be manufactured compactly, and can be fitted as a modular component, along with other modular components, to assemble an electrical socket with a 'trip' capability. The preferred embodiment as described above is small and compact enough to be used with a PDL 500 or 600 size module. The casing 100 of the standard modular sized RCD may be designed so that it can be fitted into the grid component of an electrical socket from the front (front loading). That is, after the grid component has been screwed to a mounting box typically mounted behind an aperture through a wall lining which aperture is then covered by the grid component and often a face plate to cover the gπd component, then the RCD module may be inserted from the front of the grid component into a standard module aperture in the gπd component (after wires from within the wall for example extending through this aperture have been terminated to the RCD). Figures 17 and 18 show an alternative embodiment of a modular RCD of the invention, which is a rear loading RCD module. In this embodiment the RCD module is intended to be inserted into a standard module aperture in a grid component, or combined grid faceplate where the two are combined, from the rear of the gπd component, before the gπd component is fixed in position to a mounting box for example. In Figure 17 the same reference numerals as in Figure 4 indicate the same parts of the RCD module, namely the module compnses a casing 100, a front face 103, and reset and test buttons 34 and 35. About the periphery of the forward end of the RCD module are additionally provided parts 180 which are intended to inter-engage, for example by clipping, with matching parts on the rear of the gπd, to attach the module to the grid Figure 18 shows a portion of the front face of an electrical fitting with the module attached to the rear thereof, from which it can be seen that once the module has been clipped to the grid or fitting from the rear (back loading), the front face 103 and reset and test buttons 34 and 35 of the module are exposed through a complementary shaped aperture in the fitting

Microcontroller

In all embodiments the RCD trips when a current imbalance is detected by the sensing coil 300, and iemains tripped until it is manually reset, i.e. by a user pressing the reset button.

A first embodiment of the RCD remains latched during brown-outs or loss of power supply, and onl } trips or unlatches if a fault is sensed This embodiment is useful in devices

where it is in the owners or useis best interests that the RCD trips if there is a fault, but remains latched if there is an external problem, such as intermittent power supply. For example, if an RCD assembly is used with a refrigerator or similar, it is useful for the RCD to trip if a fault is detected but remain latched if the external power supply is intermittent or 'browns-out'. This ensures that when the power supply is restored to normal operating conditions the device operates as normal without a user having to. reset the RCD.

An alternative embodiment trips and remains tripped in the event of a 'brown out' or power loss This embodiment is preferred for situations where the RCD will be used with e g. power tools, where a user will be working with the powered item closely, and will be able to reset the RCD easily if required. If for some reason the user is absent between the point at which the RCD trips, and the point at which normal power balance is restored, the RCD will remain tripped, and a plugged in power tool or similar will not activate while they are absent. For example, if there is a 'brown-out' or similar where the voltage level drops and the RCD consequently trips, it will remain tripped until reset. This is useful if the brown-out lasts for some hours, and a user has abandoned for example a plugged in power tool.

In both of these embodiments, the solenoid 501 is activated by the control circuitry on the circuit board 400. In the first embodiment, the control circuitry energises the solenoid when the mechanism is reset and de-energises it when a fault is detected (hence the mechanism described in the first embodiment also trips/activates during brown-outs or loss of supply power). In the second embodiment the solenoid is only activated to trip the RCD when a current imbalance (indicative of a fault) is detected.

In a preferred form the circuitry on circuit board 400 is based on a microcontroller design as shown in figure 19. The circuit comprises of a microcontroller 401, a sensor circuit 402, amplifier 403 and trip circuit 404. The sensor coil output from sensor circuit 402 is amplified by amplifier 403 and sent to the ADC input of the microcontroller 401 The microcontroller 401 converts the analogue input into digital form which the microcontroller 401 then uses to detect a fault current. When a fault current is detected the microcontroller 401 sends a signal to a silicon-controlled rectifier (SCR) which trips the solenoid, which in turn disconnects the power to the load. It is a desired feature to manufacture RCDs having different sensitivity level The sensitivit) level of RCD refers to the difference in current flowing between phase and neutral wires required to cause the RCD to trip i.e. recognised as a fault condition RCDs generally have three standard sensitivity levels' 6mA, 10mA and 3OmA. The sensitivity level is set at manufacture. Preferred forms of RCD of the invention allow for the sensitivity of the RCD to be set using a separate dedicated hardware set up that teaches the RCD about the sensitivity

level. When the RCD is instructed with the sensitivit) level, the microcontroller 401 sets the threshold for fault current inside the internal memory accordingh . When current imbalance between phase and neutral lines is detected during normal operation, the microcontroller 401 will only send a signal to the SCR if the current imbalance is above the threshold set in memory. In existing RCDs, the sensitivity and tripping time both vary because of tolerance levels of the electronic components within the circuitry. Coils in particular can have ^25% variation in their inductance level. A preferred form of the RCD of the present invention adjusts these variations within the firmware using the same hardware set up, as above. During calibration, a fault current of for example 6mA, 1OmA or 30mA is passed through the coil; the output of the coil passes through amplifier 403 to the microcontroller 401. The output of die coil may vary due to die tolerance of the electronic components in the current sensing and amplifier stages. The microcontroller 401 is arranged to compute the difference between the operational amplifier 403 output and the standard fault currents. This difference is offset by the microcontroller 401. After offsetting the difference between the input fault current and the output current of the operational amplifier 403, two threshold values are stored in the microcontroller 401: one for the highest threshold and, one for the lowest threshold. In use, a detected current imbalance is then compared by the microcontroller against both thresholds to increase accuracy in assessing whether a detected fault current falls within or above the required sensitivity level.

Figure 20 shows a possible embodiment for the microcontroller's 401 functional flowchart 420. At step 421 the system is initialized. A check is first made to ensure the SCR has not activated the solenoid 422. At step 423 the microcontroller 401 checks whether it is in the calibration mode. If so the microcontroller 401 records the output current from the operational amplifier 403 taking note of the absolute highest and lowest current values 425. Once calibration has ended, the highest and lowest current values are stored in memory as the threshold values 427 and the microcontroller 401 returns to step 423. The microcontroller begins to acquire the value of the current output from the operational amplifier 403 and check if the value exceeds the thresholds 429. If so, the solenoid is activated and the circuit is tripped, otherwise the microcontroller returns to step 423.

The sensitivity and calibration settings are done at manufacture. After manufacture these settings cannot be altered. The testing μg for calibration may consist of a calibrated current source 431 and a bed of nails 432 capable of shorting the calibration pins on the RCD PCB board, which subsequendy places the unit in the calibration state A fault current can then be passed through the coil as discussed above to calibrate the device

In a preferred embodiment, an automatic self test is performed periodically (e.g. weekly) to determine the integrity of the RCD circuitry and the mam contacts. A test program instructed

to run weekl) checks the circuit functionality With a successful self test, the main contacts will remain closed The entire self test is performed in less than 100ms. During this time power is not interrupted. Moreover, the circuit is designed to detect residual current faults during the self test sequence to provide additional safety If the RCD fails an automatic self test, it will attempt to trip out This is because the RCD should not remain in circuit if it no longer offers any protection.

In a preferred embodiment diere is provision for the microcontroller to monitor the zero crossing and peak state of the AC mains. In case of a fault condition the microcontroller sends a signal to the SCR so that die circuit opens at a specific wave band only. This prevents arcing at the switching contacts and preserves the life of the main contacts.

In existing RCDs, swapping load and line wires could result in fatal damage to the RCD (and cause fire). In a preferred embodiment an auxiliary contact is used to indicate wrong wiring by flashing an LED visible on the front face of the RCD. The load is also disconnected immediately. Arcing can occur in the wiring, contacts, or switches. This can cause fire for example. A preferred embodiment of the RCD is arranged to monitor the mains waveform periodically, detect disturbances in the waveform caused by arcing, and trip the RCD if there is a distribance.

A preferred embodiment of the RCD is also arranged to protect die unit from overheating due to high current or internal component faults, and trip the RCD if overheating is detected.