Field of the Invention

The present invention relates to an electrical device, particularly for connection to an extractor fan with an overrun timer.

Extractor fans of the kind that are used in public and domestic toilets are often connected in parallel with the lighting for the toilet. Such fans are often fitted with an overrun timer which allows the fan to continue to operate even after the lights have been switched off.

The fan is provided with a neutral connection, a permanent live connection and a switched live connection which is interrupted by the light switch. When the power supply to the switched live connection is interrupted, the fan continues to be powered by the permanent live connection for a period of time controlled by the overrun timer.

It is desirable to protect such extractor fans with the same fuse for both the permanent live and the switch live. However, in many commercial installations this is not practical as the extractor fan circuit includes a lighting load. Consequently, if a single fuse is located - - -between the live-supply and the lighting load to-protect-th& extractor fan, the- supply to the lights will also be interrupted when the fuse blows.

The present invention provides a simple electrical device which can protect both the permanent live and the switched live connections of an extractor fan with a single fuse.

According to the present invention, there is provided an electrical device for connection between respective inbound neutral, permanent live and switched live connections and respective outbound neutral, permanent live and switched live connections. The device comprises: a fuse device between the inbound permanent live connection and the outbound permanent live connection; a switch controller between the inbound switched live connection and a neutral connection; a switch operable by the switch controller in use to connect the inbound permanent live via the fuse device to the outbound switched live connection, whereby the fuse device protects both the outbound permanent live connection and the outbound switched live connection.

According to the invention, the supply to the outbound switched live connection is provided from the inbound permanent live connection via the fuse device and the controlled switch. The controlled switch is closed when the switch controller is energised by current between the inbound switched live connection and the outbound neutral connection. In this way, a single fuse device protects both the outbound permanent live connection and the outbound switched live connection.

The switch controller may be any device that is capable of closing the switch when supplied with current. For example, the switch controller may be a suitable electronic device. In the presently preferred embodiment, the switch controller is a relay coil.

The fuse device may be any device that is capable of interrupting current flow in response to excessive current through the fuse device. For example, the fuse device may be a circuit breaker, preferably a miniature circuit breaker. In the presently preferred embodiment, the fuse device is a fuse.

Desirably, the electrical device is contained within a housing that includes access for the inbound and outbound connections. For example, the device may be contained within a housing corresponding in size to that for a standard fuse spur. The configuration of

standard fuse spurs and sockets are defined, for example, in British Standards BS4662 and BS1363 and European Norm EN60669.1

Conveniently, the electrical device may comprise an isolator switch arranged to break at least one of the inbound connections. Preferably, the isolator switch is arranged to break at least the inbound live connections. In the presently preferred embodiment, the isolator switch is a three-pole single throw isolator switch arranged to break each of the inbound connections.

Desirably, the isolator switch is located in the housing of the electrical device to provide a combined isolator switch and fuse. Desirably, this housing corresponds in size to a standard switch box or fuse spur.

Brief Description of the Figures

An embodiment of the invention will now be described by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a circuit diagram showing the connection of a lamp and extractor fan to a mains supply;

Figure 2 is a circuit diagram in which the electrical device according to an embodiment of the invention has been incorporated into the circuit of Figure 1.

Detailed Description of the Figures

Figure 1 illustrates a known configuration for connection of a lamp 1 and an extractor fan 2 to a mains supply 3.

As shown in Figure 1, the live connection L from the mains supply 3 is protected by a main fuse 4. The main fuse 4 protects both the lamp 1 and the extractor fan 2. Consequently, the main fuse 4 must be rated sufficiently highly that it does not trip under normal operation of the lamp 1 (or lamps). Typically therefore, a three amp fuse is used

in this position. In series with the main fuse 4 is a two-pole, single-throw isolator switch 5 which can interrupt both the neutral N and live L connections from the mains supply 3.

The lamp 1 is connected in parallel between the neutral connection N from the two-pole isolator switch 5 and a switched live connection Ls in a ceiling junction 6. In the ceiling junction 6, the live connection L from the two-pole isolator switch 5 is connected to a pull switch 7. The pull switch 7 is connected between the live connection at the ceiling junction 6 and the switched live connection at the ceiling junction 6. Consequently, when the pull switch 7 is closed, the switched live connection is live and the lamp 1 lights. When the pull switch 7 is open, the switched live connection is broken and the lamp 1 is off. The pull switch 7 is by way of example only and any other type of switch could also be used.

The circuit shown in Figure 1 further includes a three-pole, single-throw isolator switch 8 which is connected to the neutral N, switched live Ls and live L connections at the ceiling junction 6. The extractor fan 2 has three electrical connections: a permanent live connection L, a switched live connection Ls and a neutral connection N. The live L, switched live Ls and neutral N connections of the extractor fan 2 are connected to the corresponding outbound connections of the three-pole isolator switch 8, such that the three-pole isolator switch 8 can make or break all connections to the extractor fan 2. The three-pole isolator switch 8 is a recommended, but optional, component of the circuit and allows the extractor fan 2 to be electrically isolated for maintenance.

The permanent live connection L provides the power to the motor of the extractor fan 2. When the pull switch 7 is activated, the switched live connection Ls goes live and the extractor fan 2 begins to operate. When the supply to the switched live connection Ls is interrupted by opening of the pull switch 7, the extractor fan 2 continues to operate under the control of an overrun timer for a predetermined period of time.

It is generally recommended that the extractor fan 2 is protected by a single fuse to the live L and switched live Ls connections. In the circuit shown in Figure 1, the only fuse is the three amp main fuse 4 which protects all live connections, but when tripped interrupts the power supply to both the lamp 1 and the extractor fan 2. This is undesirable in a

bathroom or toilet installation, where the malfunction of the extractor fan 2 could result in darkness.

Figure 2 shows a circuit diagram incorporating the invention. Corresponding components are given the same reference numerals as in Figure 1 and will not be described in detail for the avoidance of repetition.

As shown in Figure 2, the three-pole isolator switch is provided in a housing, together with a relay 9 and a fan fuse 10. According to the invention, the fan fuse 10 is a one or two amp fuse conforming to British Standard 1362. The fan fuse 10 is connected between the live switch of the three-pole isolator switch 8 and the live connection L to the extractor fan 2. In parallel with the live connection L to the extractor fan 2, the switch 9b of the relay 9 is connected between the fan fuse 10 and the switched live connection of the extractor fan 2. The coil 9a of the relay 9 is connected between the switched live switch of the three-pole isolator switch 8 and the neutral connection N to the extractor fan 2.

When the switched live connection Ls from the ceiling junction 6 is live, the relay coil 9a is energised and closes the relay switch 9b to provide power from the permanent live connection L at the ceiling junction 6 to the switched live connection Ls of the extractor fan 2 via the fan fuse 10. When the power to the switched live connection Ls at the ceiling junction 6 is interrupted, the relay coil 9a is not energised and the relay switch 9b is open, interrupting the switched live connection Ls to the extractor fan 2.

In the event of a power surge, the fan fuse 10 breaks the connection to both the live L and switched live Ls connections of the extractor fan 2. In this way, a single fan fuse 10 protects both the live L and switched live Ls connections of the extractor fan 2, without interrupting the power supply to the lamp 1.

Conveniently, the isolator switch 8, fan fuse 10 and relay 9 are provided in a single housing corresponding in size to a standard switch box or fuse spur. In this way, the device according to the invention can easily replace an existing three-pole isolator switch 8. Alternatively, the device may also be housed in a double socket sized housing.

It will be appreciated that it is not necessary for the relay coil 9a to be connected to the neutral connection N of the extractor fan 2. It is only necessary that the relay coil 9a is energised when the switched live connection Ls from the ceiling junction 6 is live. For example, it is possible for the relay coil 9a to be connected between a switched live connection and an earth connection or a separate neutral connection.

Furthermore, although the three-pole isolator switch 8 has been included in the housing for the fan fuse 10 and the relay 9 in the embodiment shown, this is not essential. For example, the fan fuse 10 and the relay 9 may be included in a separate housing with the three-pole isolator switch 8 provided separately, if at all. The three-pole isolator switch 8 may be in the form of a pull cord switch. In this case, the device may be housed in a pull cord switch housing.

In summary, there is disclosed herein an electrical device for connection between respective inbound neutral, permanent live and switched live connections and the neutral, permanent live and switched live connections of an extractor fan with an overrun timer.

A fuse is provided between the inbound permanent live connection and the permanent live connection of the extractor fan A relay coil is provided between the inbound switched live connection and a neutral connection. A switch is operated by the relay coil to connect the inbound permanent live via the fuse to the switched live connection of the extractor fan. In this way, the fuse protects both the live and switched live connections of the extractor fan.