GB2348543A

GB2348543A - Circuit breaker

Info

Publication number: GB2348543A
Application number: GB9907548A
Authority: GB
Inventors: Keith Woolston; Mark Christian David Woolston
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-04-01
Filing date: 1999-04-01
Publication date: 2000-10-04
Also published as: GB9907548D0

Abstract

A circuit breaker for use with a fault detection circuit in connecting a power supply and a load comprises a housing 110, an actuator 114 movable relative to the housing from a first position to a second position, a stationary contact 134, a movable contact 132 mounted on the actuator 114 and a switch 138. When the actuator is in the first position the stationary and movable contacts do not engage. One of the stationary contact and movable contact is resiliently biassed toward the other such that when the actuator is operated from the first position to the second position the movable and stationary contacts engage to provide an electrically conductive path between the power supply and the load before the actuator reaches the second position at which it actuates the switch 138 which enables an electrical current to flow between the power source and the load via the contacts.

Description

Electrical Switch The present invention relates to an electrical switch, and in particular to an electrical switch used as a circuit breaker for safely controlling the connection of a power supply and a load.

A circuit breaker is used to control the supply of electrical power from a power supply to a load. They can be used with high electrical power equipment which is potentially dangerous. Some circuit breakers are manually reset once they have broken the circuit. Hence an important requirement of a circuit breaker is that it is safe for manual operation. The safe operation of a circuit breaker, and in particular preventing electrical arcing owing to the large voltages involved, is important in terms of preventing harm to the user, preventing damage to the circuit breaker, preventing fire risks from the electrical arc and/or damage to the circuit breaker, and preventing damage to electrical equipment connected to the circuit breaker.

Fault detection circuits are well known in the art and can be used in conjunction with a circuit breaker to monitor the electrical power supplied from the source to the load and provide a control signal for use by the circuit breaker when abnormalities are detected.

According to an aspect of the invention, there is provided a circuit breaker for use with a fault detection circuit in connecting a power supply and a load, and comprising a housing, an actuator movable relative to the housing from a first position to a second position, a stationary contact, a movable contact mounted on the actuator, and a switch, in which when the actuator is in the first position the stationary and movable contacts do not engage, and one of the stationary contact and movable contact is resiliently biassed toward the other such that when the actuator is operated from the first position to the second position the movable and stationary contacts engage to provide an electrically conductive path between the power supply and the load before the actuator reaches the second position at which it actuates the switch which enables an electrical current to flow between the power source and the load via the conductive path provided by the contacts.

The circuit breaker of the current invention has two contacts which when engaged provide an electrically conductive path between the load and power supply along which an electrical current between the load and power supply can flow. One of the contacts is mounted on an actuator so that it is movable relative to the other contact. Either the movable or stationary contacts is resiliently biassed toward the other. A switch is provided which controls whether an electrical current is supplied to the contacts. The contacts are arranged so that when the actuator is operated, the contacts are brought into engagement before the actuator operates the switch to enable current to flow through the path provided by the contacts.

The resilient biassing of one of the contacts accommodates the extra movement of the actuator that needs to occur before it can actuate the switch. As no electrical power is supplied to the contacts before they engage, arcing is obviated as an electrically conductive path is already present before the supply of current to the path is enabled by the switch.

As arcing is precluded by the circuit breaker of the present invention, it will be appreciated that a number of safety advantages are provided. Arcs are eliminated and so the circuit breaker is suitable for use in environments with flammable materials. Electric shocks to the user are avoided. Damage to the circuit breaker itself by arcing is removed providing a more durable and safer circuit breaker.

The circuit breaker can include a latch, in which when the actuator actuates the switch, the switch enables operation of the latch to hold the actuator in the second position.

In this manner a single switch serves the joint purposes of enabling electrical power to flow and also causing the actuator to be held in position to maintain the electrical path via the engaged contacts. As the switch concomitantly causes the actuator to be locked in position and enables the supply of power to the contacts, the circuit breaker only becomes live once the actuator has locked at which stage a user need not be in contact with the circuit breaker, further adding to its safety of operation. The device is effectively isolated.

The circuit breaker can have the stationary contact biassed toward the movable contact. The movable contact can be biassed toward the stationary contact. Both the movable and the stationary contact can be biassed toward each other.

The biassing of the contact accommodates the motion of the actuator relative to the contacts that the actuator undergoes once the contacts are engaged so as to subsequently actuate the switch.

Preferably, the circuit breaker included a second fixed contact and a second movable contact, in which when the actuator is in the first position the second fixed contact and second movable contact engage to provide an electrically conducting path. A second electrically conducting path can be provided by a second set of fixed and movable contacts which are engaged when the actuator is in the first position. The second set of contacts provides a switch for a second control of the circuit breaker. When the actuator is returned into the first position the second contacts automatically re-engage. Hence the second contacts are particularly suitable for providing a reset control signal as they only engage when the first set of contacts are disengaged.

Preferably, as the actuator is moved out of the first position the second fixed contact and second movable contact disengage. The second set of contacts disengage as soon as the actuator is moved out of the first position. Hence it is possible to configure the circuit breaker such that neither the first nor the second sets of contacts engage at the same time.

The circuit breaker can include a reset device which is activated when the fixed and movable contacts are engaged to allow the circuit breaker to operate. If the second contacts are not engaged to activate the reset device then the circuit breaker prevents the current passing across the path provided by the first contacts even though they are in contact. The reset device prevents the circuit breaker from operating to allow a current to pass from the source to the load if the reset device is not activated by the second set of contacts.

Preferably, the reset device is connected to the switch to enable actuation of the latch only when the reset device has been activated. The reset device can also be connected to the switch so as to prevent the switch from enabling the latching of the actuator unless the reset device has been activated. Hence, the latch can only operate once the reset device has been activated by the second set of contacts engaging. The reset device provides a means of both preventing latching of the actuator and preventing current flow through the first set of contacts even when they provide an electrically conductive path. The reset device can include a capacitor. Activation of the reset device can include charging the capacitor by connecting it to an electrical power supply via the second set of contacts.

Preferably, the actuator includes a conductive part and the latch includes a winding which passes around the conductive part so as electromagnetically to hold the actuator in the second position when the latch actuated. The latch can be provided by a coil through which the actuator passes and actuator having a conductive part so that the actuator can be latched in the second position by the electromagnetic action of the coil on the actuator.

The circuit breaker can include a biassing means which biases the actuator into the first position. In this way. the default position of the actuator is the first position.

Unless the latch is operating the actuator will return to the first position thereby ensuring that the load and power supply remain disconnected. The biassing means also ensures that the second set of contacts are engaged thereby automatically resetting the circuit breaker.

The circuit breaker can include an operating button operable to engage the actuator and move the actuator into the second position. The operating button is manually operable by a user to move the actuator into the second position and activate the circuit breaker to supply power to the load.

Preferably the stationary contact includes a pair of contacts and the movable contact includes a pair of contacts and the pairs of contacts are in registration so that a respective contact of the pairs of contacts engage. A respective contact of each of the pairs are in registration so as to provide two electrically conducting paths when they engage, so as to provide separate paths for live and neutral electrical signals.

According to a further aspect of the invention, there is provided a circuit breaker for use with a fault detection~ circuit in connecting a power supply and a load, and comprising a housing, an actuator movable relative to the housing from a first position to a second position, a stationary contact, a movable contact mounted on the actuator, a latch and a switch, in which when the actuator is in the first position the stationary and movable contacts engage to activate a reset device such that as the actuator is operated from the first position to the second position the movable and stationary contacts disengage and as the actuator reaches the second position it actuates the switch which co-operates with the reset device to enable operation of the latch to hold the actuator in the second position.

The circuit breaker is provided with a set of contacts which engage when the actuator is in a first position to cause a reset device to be activated. The reset device and switch co-operate, when the switch is activated by the actuator in its second position, so as to cause the actuator to latch in the second position. If the contacts are not engaged to activate the reset device, then the actuator does not latch in the second position and so the circuit breaker cannot be operated.

According to a further aspect of the invention, there is provided, a circuit breaker for use with a fault detection circuit in connecting a power supply and a load, and comprising a housing, an actuator movable relative to the housing from a first position to a second position, a first stationary contact, a first movable contact mounted on the actuator, a second stationary contact, a second movable contact mounted on the actuator, and a switch, in which when the actuator is in the first position the first stationary and first movable contacts engage to activate a reset device such that as the actuator is operated from the first position to the second position the first movable and first stationary contacts disengage, and when the actuator reaches the second position it actuates the switch which co-operates with the reset device to enable a current to flow between the load and power supply via the second stationary and movable contacts.

The circuit breaker is provided with a first set of contacts which engage when the actuator is in a first position to cause a reset device to be activated. The circuit breaker is also provided with a second set of contacts, which provide a conducting path between the power supply and load, and which can engage before the actuator activates the switch in the second position. The reset device and switch co-operate, when the switch is activated by the actuator in its second position, so as to enable a current to pass from the power supply to the load. If the first set of contacts are not engaged to activate the reset device, then the reset device and switch do not permit a current to pass via the second set of contacts and so the circuit breaker cannot be operated, even if the second set of contacts are manually held in engagement.

An embodiment of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a cross sectional view of a circuit breaker according to the invention, with an actuator in a first position; Figure 2 shows a cross sectional view of the circuit breaker of Figure 1, with the actuator in an intermediate position; Figure 3 shows a cross sectional view of the circuit breaker of Figure 1, with the actuator in an second position; Figure 4 shows a cross sectional view of the circuit breaker of Figure 1, with the actuator latched in the second position; and Figure 5 shows a schematic circuit diagram including a circuit breaker according to the invention.

The same items in different Figures share common reference numerals.

With reference to Figures 1 to 4 there are shown cross sectional side views of a circuit breaker, designated generally by reference numeral 100, according to the present invention. The circuit breaker has a housing 110 defin-ng an internal cavity 112. An actuator 114 is provided in the housing and located within the cavity. The actuator is in the form of a right circular cylindrical barrel. The actuator can move relative to the housing and along a longitudinal axis of the housing. The actuator includes a conductive metal insert 116. A coil 117 is wound around the housing to provide a part of an electromagnetic latch as will be described later. A first end of the actuator 118 bears a first electrical contact 120. The first electrical contact is a movable contact as it moves with the actuator barrel. A further electrical contact 122 is provided borne on the housing. This contact is a stationary contact.

Contacts 120 and 122 provide a first set of contacts providing a switch 124 part of a reset mechanism as wil be described later contacts.

A spring 126 engaging about a second end of the barrel provides a resilient biassing means which urges the contacts 120 and 122 together. A pair of electrical contacts 128 are provided toward a second end 130 of the actuator. The pair of contacts are mounted on the actuator by a leaf spring 132 which provides a resilient biassing means. Another pair of electrical contacts 134 are also provided at a second end of the housing 110. The contacts of a pair are in registration with the respective contacts of the other pair. The contacts 128 on the actuator are movable contacts and the contacts 134 at the second end of the housing are stationary contacts. The movable contacts 128 are resiliently biassed by the leaf spring towards the stationary contacts 134.

Electrical contacts 132 and 134 provide a second set of contacts which can provide two conductive paths of a switch 136 between a power supply and load as will be described later.

A switch 138 is provided below the actuator and which forms part of a reset circuit as will be described later.

A first end of the housing 139 includes a manually operable button 140 located in a cavity. The button has an extended stem 142 which is directed toward the first end of the barrel. A spring 144 is provided to resiliently bias the button away from the barrel. The button is captured in the cavity by notches 146 co-operating with the button edge 148.

The actuator barrel is shown in Figure 1 in a first position, in which the first set of contacts 120,122 are engaged. The second set of contacts 128,134 are not engaged and the circuit breaker is inactive.

Operation of the circuit breaker in conjunction with a fault detection circuit to connect a power supply to a load will now be described with further reference to Figure 5. Figure 5 shows a schematic circuit diagram illustrating use of the circuit breaker. The circuit breaker is used with a fault detection circuit 142 which is of conventional design in this field of art. The output of a 240V ac supply is provided to the fault detection circuit from an electrical power supply on two lines. A transformer 141 provides a low voltage dc supply to the fault detection circuit to provide operating power. A latch signal is provided by the fault detection circuit to the winding 117 of the circuit breaker via a triac 146 to provide an electromagnetic latch mechanism. The triac 146 is controlled by a reset circuit signal as will be described later. The 240V ac is output on two lines from the fault detection circuit 142 and provided to a switch 136 provided by the second set of contacts of the circuit breaker via a first transistor 143 and a second transistor 144. The transistors 143,144 are controlled by an electrical signal from the triac which in turn is controlled by a signal from a reset circuit 150.

The reset circuitry provides that after a fault has occurred and the circuit breaker has stopped passing power to the load, the circuit breaker can only operate to pass electrical power to the load once the circuit breaker has been reset'back into an operable condition.

The reset circuit 150 is provided in parallel with the fault detection circuit. The reset circuit includes the first set of contacts providing switch 124 in series with capacitor 148 which provides a reset device further in series with switch 138 which is actuable by the actuator 114. The reset circuit provides a reset signal which controls the output of the triac 146. Hence the reset circuit can provide a signal which can enable operation of the triac 146. Part of the output signal from the triac is connected to the base of each of the transistors 143,144 so that they can be enabled to pass the main power current to the switch 136.

With the actuator in thefirst position as shown in Figure 1, the first contacts~l22 and 120 are engaged and switch 124 is closed. Switch 138 is open. The reset device capacitor 148 is activated and charges up. Switch 136 provided by the second set of contacts is open and so the load and supply are isolated. As there is no reset signal provided to triac 146, no latch signal is enabled to be provided from the fault detection circuit to the latch windings 117. Further as triac 146 is not enabled, there is no signal to transistors 143,144 and so no electrical current is supplied through transistors 143,144 to the switch contacts 134.

When button 140 is manually operated, as shown in Figure 2, contacts 120 and 122 disengage and switch 124 is opened. As the actuator moves downward in Figure 2, the movable contacts 128 engage the stationary contacts, at an intermediate position of the actuator, providing a pair of electrically conducting paths and closing switch 136 of Figure 5. However, as switch 138 is still open as it has not been actuated by the actuator end 130, no enable signal is present to activate triac 146 and so no enable signal is provided to the transistors 144 and so no electrical current passes to the contacts. Hence electrical arcing is precluded as a conducting path is provided before an electrical signal is provided to the main power switch 136.

The switch is 136 is isolated.

As the button is fully depressed, the actuator continues moving downward and pairs of contacts 128 and 134 remain stationary with the leaf spring accommodating the further motion of the actuator. The actuator reaches a second position as shown in Figure 3, in which the end of the actuator 130 actuates and closes switch 138. This allows capacitor 148 to discharge providing a reset signal enabling the triac 146 to pass an output latch signal from the fault detection circuit to energise the winding 117 which co-operates with the conductive insert to electromagnetically latch the actuator in the second position. The signal passed by the triac also enables the transistors 143,144 to allow the current to pass from the fault detection circuit through the transistors and through switch 136 to the load. As an electrically conducting path is present before the current, the build up of a large voltage prior to closing the contacts is precluded and arcing is prevented.

The push button 140 can be released and the actuator is electromagnetically latched in the second position with switches 138 and 136 closed, as shown in Figure 4.

If a fault in the power supplied to the load is detected by the fault detection circuit, then the latching signal provided to the triac is removed and spring 126 causes the actuator to return to the first position, opening switch 136 and isolating the load and power supply. In the first position, contacts 120 and 122 automatically engage closing switch 124 and activating the reset device by charging up capacitor 148.

It will be appreciated that switches 124,138 and capacitor 148 provide a circuit that resets the circuit breaker for correct operation, as if the capacitor is not recharged, then the circuit breaker will not operate to allow current to pass from the power supply to the load. The triac will only pass a signal if the capacitor has been re-charged and can enable it. In the absence of the signal from the traic, the latch cannot operate. Further, the transistors 143,144 cannot be enabled and so power will not be transmitted to the switch 136. Hence, even if the actuator is held down to engage contacts 128 and 134, no electrical power can be provided to the load. The capacitor must be recharged by returning the actuator to the first position so as to close switch 124. If a fault is detected, then the circuit breaker has to return to its reset position before power can be supplied to the load, assuming a no-fault condition detected by the fault detection circuit.

Although the movable contacts are shown as being resiliently biassed, it will be appreciated that the stationary contacts 134 could be provided with resilient supports as well or alternatively. Further, although contacts 134 are referred to as stationary it will be appreciated that all that is required to effect an aspect of the invention is that there be relative movement between the contacts 128 and 134 so that they can be brought into contact before switch 138 is actuated. The term stationary is merely to distinguish them from the contacts mounted on the actuator.

Numerous advantages are provided by the various aspects of this invention. The absence of arcing means that the circuit breaker is suitable for use in flammable environments. The compact construction makes the circuit breaker smaller than previously provided devices owing to its differing actuation geometry. Power is only supplied to the load after the switch locks and so the user does not handle the circuit breaker while it is already active. If a fault is detected, then the circuit breaker has to return to its reset position before it can be operated again and therefore power will be available. The circuit breaker provides extremely good isolation.

Claims

CLAIMS:

1. A circuit breaker for use with a fault detection circuit in connecting a power supply and a load, and comprising: a housing; an actuator movable relative to the housing from a first position to a second position; a stationary contact; a movable contact mounted on the actuator; and a switch, in which when the actuator is in the first position the stationary and movable contacts do not engage, and one of the stationary contact and movable contact is resiliently biassed toward the other such that when the actuator is operated from the first position to the second position the movable and stationary contacts engage to provide an electrically conductive path between the powersupply and the load before the actuator reaches the second position at which it actuates the switch which enables an electrical current to flow between the power source and the load via the contacts.

2. A circuit breaker as claimed in claim 1 and including a latch, in which when the actuator actuates the switch, the switch enables operation of the latch to hold the actuator in the second position.

3. A circuit breaker as claimed in claim 1, in which the stationary contact is biassed toward the movable contact.

4. A circuit breaker as claimed in claim 1, in which the movable contact is biassed toward the stationary contact.

5. A circuit breaker as claimed in claim 1 and including a second fixed contact and a second movable contact, in which when the actuator is in the first position the second fixed contact and second movable contact engage to provide an electrically conducting path.

6. A circuit breaker as claimed in claim 5, in which as the actuator is moved out of the first position the second fixed contact and second movable contact disengage.

7. A circuit breaker as claimed in claim 5 or claim 6, and including a reset device which is activated when the fixed and movable contacts are engaged to allow the circuit breaker to be operated.

8. A circuit breaker as claimed in claim 7, in which the reset device is connected to the switch to enable actuation of the latch only when the reset device has been activated.

9. A circuit breaker as claimed in claim 1, in which the actuator includes a conductive part and the latch includes a winding which passes around the conductive part so as electromagnetically to hold the actuator in the second position when the latch actuated.

10. A circuit breaker as claimed in claim 1, and including a biassing means which biases the actuator into the first position.

11. A circuit breaker as claimed in claim 1, and including an operating button operable to engage the actuator and move the actuator into the second position.

12. A circuit breaker as claimed in claim 1, in which the stationary contact includes a pair of contacts and the movable contact includes a pair of contacts and the pairs of contacts are in registration so that a respective contact of the pairs of contacts engage.

13. A circuit breaker for use with a fault detection circuit in connecting a power supply and a load, and comprising: a housing; an actuator movable relative to the housing from a first position to a second position; a stationary contact; a movable contact mounted on the actuator; a latch; and a switch, in which when the actuator is in the first position the stationary and movable contacts engage ~ activate a reset device such that as the actuator is operated from the first position to the second position the movable and stationary contacts disengage and as the actuator reaches the second position it actuates the switch which co-operates with reset device to enable operation of the latch to hold the actuator in the second position.

14. A circuit breaker for use with a fault detection circuit in connecting a power supply and a load, and comprising: a housing ; an actuator movable relative to the housing from a first position to a second position; a first stationary contact; a first movable contact mounted on the actuator; a second stationary contact ; a second movable contact mounted on the actuator; and a switch, in which when the actuator is in the first position the first stationary and first movable contacts engage to activate a reset device such that as the actuator is operated from the first position to the second position the first movable and first stationary contacts disengage, and when the actuator reaches the second position it actuates the switch which co-operates with the reset device to enable a current to flow between the load and power supply via the second stationary and movable contacts.