GB2204736A - Residual current circuit breakers for sockets - Google Patents

Abstract

A RCCB comprises an outgoing supply socket, a circuit breaker mechanism for interrupting the flow of current to the supply socket in response to a fault signal, and means responsive to the absence of a plug (1) in the supply socket for reducing the energy required to close the contacts (8,9) of the breaker mechanism. The reduced energy requirement is achieved either by reducing the contact gap of the breaker mechanism or by reducing the magnitude of a biasing force tending to open the contact gap. As shown, removal of the plug (1) allows the socket shutter (2) to be spring-biased to the left, to move the contact (9) closer to the fixed contact (8) and hence allow the electromagnet (4) to reclose the contacts without manual intervention. Alternatively, a spring is provided between the movable contact (9) and the shutter (2) to provide contact bias to the open position in conjunction with the armature spring. On plug removal, the shutter movement reduces the bias provided by the contact/shutter spring. A further contact can be provided on the shutter (2) for closing with the movable contact (9) in the absence of a plug, for test purposes. <IMAGE>

Description

RESIDUAL CURRENT CIRCUIT BREAKERS In a residual current circuit breaker (RCCB) where the circuit is broken by opening a pair of contacts, the contact opening force must be high enough to ensure reliable opening, and the resulting contact gap must be large enough to ensure adequate isolation. Accordingly, considerable electrical energy is required by a conventional electromagnetic actuator, such as a relay or solenoid, to initially close the contacts. For this reason RCCB's usually require manual intervention when initially closing the contacts, either to close a relay and thus reduce its power to the comparatively low holding requirements, or to set up a latching machanism which requires relatively little energy to release it.

The manual intervention is usually achieved by the use of a reset button.

The need for manual intervention, combined with the need for manual testing, is a disadvantage of conventional RCCB's. It is clearly desirable to reduce the user's interaction with the RCCB to a minimum.

According to the present invention, there is provided a RCCB in which the energy required by an electromagnetic actuator to close the circuit breaker contacts is automatically reduced in response to the absence of a plug in an associated outgoing supply socket.

In this manner it becomes possible to electrically close the contacts without manual intervention before inserting a plug into the socket, while at the same time providing sufficient contact opening force for reliable opening and a sufficiently wide contact gap for adequate isolation if a fault occurs when an appliance is plugged into the socket.

In a preferred embodiment, the RCCB is provided with mechanical means interacting with the actuator to reduce or eliminate the opening movement and/or the required contact closure force in response to the absence of a plug in the outgoing supply socket.

The mechanical means preferably comprises a conventional shutter for the outgoing supply socket. The shutter normally has an associated return spring, and may also control the state of an additional spring to reduce the force urging the contacts open when the shutter is closed and the socket is vacant. Alternatively, the shutter mechanism may act as a displaceable end stop in the path of one of the contacts to control the contact gap.

The electromagnetic actuator preferably constitutes a relay incorporating a return spriing which biases the contacts to the open position. The shutter, or a spring controlled by the shutter, may then act directly on the relay contacts and/or on the relay armature to control the contact gap or the required opening force.

Two embodiments of this invention will now be described, by way of example only, with reference to the accompanying drawings, in which Fig. 1 is a diagrammatic view of a first RCCB emobodying the invention with a plug inserted in the outgoing supply socket; Fig. 2 shows the RCCB of Fig. 1 with the plug removed; Fig. 3 is a diagrammtic view of a second RCCB embodying the invention with a plug inserted in the outgoing supply socket; and Fig. 4 shows the RCCB of Fig. 3 with the plug removed.

Referring to Figs. 1 and 2, a RCCB includes an electromagnetic relay It with a fixed contact 8 and a movable contact 9 carried by an armature 7. An associated outgoing supply socket is provided with a shutter 2 so arranged as to limit the opening of the relay in the absence of a plug in the socket. Referring to Fig. 1, if a plug 1 is present in the outgoing socket, the shutter 2 is displaced to a first position in which it allows armature 7 to achieve the full contact gap necessary to ensure adequate isolation. Referring to Fig. 2, if no plug is present in the outgoing socket, the shutter return spring 3 urges the shutter to a second position in which it restricts movement of the armature 7 to reduce the contact gap.

The reduced gap means that less electrical power is required to pull in the relay, but isolation requirements are still met because no plug is present in the outgoing supply socket.

With the shutter in its second position, the contact gap is sufficiently small that the contacts of the relay can be closed by an electrical pulse without manual intervention. Such a pulse might be applied, for example, during an automatic test sequence as described in our copending applications 8805593 and 8805595. In this case, an additional contact is provided on the end face 10 of the shutter 2 for engaging the contact 9 when the relay It is in its relaxed state and the socket is vacant (Fig. 2). The detection of this electrical contact provides a check for socket vacancy in a test interlock circuit, as more fully described and separately claimed in our aforesaid applications 8805593 and 8805595.

Referring to Figs, 3 and It, the components of the RCCB are generally the same as in Figs. 1 and 2 and the same references are used to denote like parts. In this embodiment, however, the outgoing supply socket shutter 2 controls the opening force applied to the movable contact 9 of the relay 4. Control is effected through the action of an additional spring 5 which may be a compression or a tension spring. In Fig. 3, with the plug 1 inserted in the outgoing socket and the shutter 2 displaced to its first position, the additional spring 5 co-operates with the relay spring 6 to ensure that the resultant force tending to open the contacts 8, 9 is high enough for reliable opening. In Fig. It, with the plug absent and the outgoing socket vacant, the shutter 2 is urged to its second position by return spring 3, and the state of the additional spring 5 is such that the opening force applied to the contact 9 is reduced. The reduced opening force means that less electrical power is required to pull in the relay. Again, therefore, the relay contacts can be closed electrically without manual intervention.

A third embodiment may be envisaged in which the shutter 2 acts on the relay spring 6 to vary the contact opening force.

Further embodiments may be envisaged in which the preceding embodiments are combined so that movement of the shutter affects both the gap and the contact opening force.

Claims (14)

1. A RCCB comprising an outgoing supply socket, a circuit breaker mechanism for interrupting the flow of current to the supply socket in response to a fault signal, and means responsive to the absence of a plug in the supply socket for reducing the energy required to actuate the breaker mechanism.

2. A RCCB according to Claim 1 in which the reduced energy requirement is achieved by reducing the contact gap of the breaker mechanism.

3. A RCCB according to Claim 2 further comprising a shutter mechanism associated with the supply socket, the contact gap being reduced when the shutter is displaced from a first position to a second position in response to withdrawal of a plug from the socket.

It. A RCCB according to Claim 3 in which full opening of the contact gap is restricted by the shutter mechanism when the socket is vacant.

5. A RCCB according to Claim 3 or Claim It in which a movable contact of the breaker mechanism is carried on a contact arm, and the shutter mechanism controls a displaceable end stop in the path of the movable contact or contact arm.

6. A RCCB according to Claim 5 in which the contact arm comprises the armature of an electromagnetic relay.

7. A RCCB according to Claim 6 in which the end stop carries an electrical contact for engaging the moving relay contact only when the relay is in a relaxed state and the socket is vacant whereby the engaged contacts provide a path for a test signal in an auto-test sequence prior to insertion of a plug into the outgoing socket.

8. A RCCB according to Claim 1 in which the reduced energy requirement is achieved by reducing the magnitude of a biasing force tending to open the contact gap of the circuit breaker mechanism.

9. A RCCB according to Claim 8 in which the biasing force is a spring biasing force.

10. A RCCB according to Claim 9 in which the spring biasing force is dependent on the position of a shutter mechanism associated with the supply socket, the shutter mechanism being displaced from a first position to a second position in response to insertion of a plug into the socket.

11. A RCCB according to Claim 9 in which a movable contact of the breaker mechanism is carried on a contact arm, and the position of the shutter mechanism controls the state of a spring acting on the movable contact or contact arm.

12. A RCCB according to Claim 11 in which the contact arm comprises the armature of an electromagnetic relay.

13. A RCCB substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings.

14. A RCCB substantially as herein described with reference to Figs. 3 and 4 of the accompanying drawing.