GB2535992A

GB2535992A - Power socket fascia

Info

Publication number: GB2535992A
Application number: GB1503237.8A
Authority: GB
Inventors: Delamare Andrew
Original assignee: EN Twyn Ltd
Current assignee: EN Twyn Ltd
Priority date: 2015-02-26
Filing date: 2015-02-26
Publication date: 2016-09-07
Also published as: GB201503237D0; WO2016135496A1; EP3262764A1

Abstract

A power socket fascia arranged to be fitted to a power socket box, comprising a plurality of power sockets 11, at least one signal port 20 for transmission and/or reception of a signal, and a circuit board assembly (35, figure 3). The circuit board assembly comprising a processor (32, figure 3) and at least one power bus (154, 156, figure 3). Each power socket is arranged to receive a plug of an electrical device whereby corresponding coupling elements of each power socket are electrically coupled to a power line via the at least one power bus of the circuit board. The integral power bus thereby removes the need for conventional bus-bars, leaving more space between the fascia and the back of the wall box. The integrated power line communications may include HomePlug technology and the circuit board may further comprise a plurality of filters.

Description

POWER SOCKET FASCIA

Field of the Invention

The present invention relates to a power socket fascia.

Background of the Invention

Power-line communications systems allow communications signals to be transmitted over power cables. A carrier signal is modulated with a communications signal and transmitted from one point on a cable to another point. Various systems and standards of power-line communications exist for use in the home and office environment. For example, HomePlug® is the name of a family of standards aimed at providing additional networking in the home environment Devices conforming to the HomePlug® technology standard comprise pins for insertion into a power socket (or other suitable means for electrically coupling the devices to a power-line). The devices additionally comprise processing circuitry and a data port for receiving a data cable linked to a network device. Data transmitted from (or to be received by) the network device can be transferred to/from a power-line by means of the HomePlug® device located in the power socket. In uploading a data signal to the power-line, the processing circuitry HomePlug® device processes the data signal received from the network device and subsequently uploads the processed data signal to the power-line through the pins of the HomePlug® device. Downloading a data signal from the power-line to the network device occurs in a similar manner, but the steps are reversed. A system incorporating such HomePlug® devices allows the network device to communicate with another network device coupled to the power-line via another HomePlug® device by using the power-line as the data signal transmission medium.

Alternative devices to adapters include power socket fascias such as those disclosed in GB 2,450,904 A, which is a UK patent application in the name of the applicant, En-Twyn Limited. The contents of GB 2,450,904 A are incorporated herein by reference. In such a fascia, the communications port is formed in the front face of a standard power wall socket. The power-line processor and other components are formed behind the fascia. Such a device has the benefit of removing the clutter produced by adapter devices, while also making the power sockets in the fascia available to other electrical devices. WO 2009/007730 A2, in the name of the applicant, discloses a power socket fascia, which includes power-line communications equipment and an operating system. The contents of WO 2009/007730 are also incorporated herein by reference. The inclusion of an operating system allows for more sophisticated network control.

In a traditional multi-gang power sockets fascia there is a set of bars (commonly referred to in the art as "bus bars") that respectively join the live, neutral and earth connections of a power socket to corresponding connections of the remaining power sockets of the multi-gang power sockets fascia. Each of the bus-bars are in turn respectively connected to the live, neutral and earth wires of a power-line cable, thereby allowing power to be supplied to the power sockets.

An example of the bus-bars connections behind a double-gang power socket fascia 100 is illustrated in Figure 1. As shown in Figure 1, the live connections 106a, 106b of each socket are connected to each other by bus bar 116, the neutral connections 104a, 104b are connected to each other by bus bar 114, and the earth connections 102a, 102b are connected to each other by bus bar 112. Wiring connections are provided at a top-centre section of the fascia 100, including a live connector 126, a neutral connector 124, and an earth connector 122. As shown in Figure 1, the bus bars 112, 114, 116 are respectively connected to these connectors. The wires of the power-line cable (not shown) are then connected to the respective connectors and placed into the top-centre section of fascia 100 which when in place constitutes the centre of a standard wall box.

As known in the art, bus bars are made of fairly bulky metal bars or copper strips that occupy a substantial amount of the internal space between the fascia and the back of the wall box. This leaves very limited space for devices, such as those described in GB 2,450,904 A and WO 2009/007730 A2, to be installed within a multi-gang power socket Thus, the present invention seeks to provide an improved power socket fascia that maximises the available internal space between the power socket fascia and the back of a wall box.

Further problems associated with prior art devices have also been identified. In particular, it has been noted that a power-line device, such as those described in the above paragraphs, plugged in a multi-gang socket fascia is subjected to electromagnetic interference (EMI) (or "noise") when a multi-gang power sockets extension is plugged in a neighbouring socket of the same multi-gang power socket fascia. The interference is particularly high when electrical devices, such as laptops and mobile phone chargers, are plugged in the multi-gang power sockets extension. This is caused by noise generated by those electrical devices travelling through the extension cable of the multi-gang sockets extension and into the socket in which the power-line device is plugged in. Consequently, this has an effect on the performance of the power-line device in maintaining a reliable connection.

1Therefore, the present invention further seeks to provide an improved power socket fascia Therefore, the present invention further seeks to provide an improved power socket fascia that reduces EMI on a power-line device, particularly when the power-line device is plugged in a common multi-gang power sockets fascia as a multi-gang power sockets extension having electrical devices connected to it.

Summary of the Invention

In a first aspect the present invention provides a power socket fascia arranged to be fitted to a power socket box, comprising: a plurality of power sockets, each power socket arranged to receive a plug of an electrical device and each power socket including coupling elements; at least one signal port for transmission and/or reception of a signal; and a circuit board assembly comprising a processor coupled to said at least one signal port and arranged to be electrically coupled to said power-line and arranged to transfer a signal between said at least one signal port and said power-line so that said signal can be transmitted and/or received from said power-line, said circuit board assembly further comprising at least one power bus through which one of the coupling elements of one of said plurality of power sockets is coupled to a corresponding coupling element of at least one other said plurality of power sockets, and wherein said power bus is further arranged to be electrically coupled to the power-line.

The advantage of the present invention is that the internal space of the power socket box is maximised by providing the power bus on the same circuit board as the processor.

Preferably, said at least one power bus includes at least one conductive track formed on a surface of said circuit board. This provides a further advantage of easy manufacturing process as the conductive tracks can be formed together with printed circuit tracks printed on the surface of the circuit board during manufacturing. Furthermore the assembly process is further simplified by replacing metal power bus bars (or copper strips) with printed conductive tracks.

The conductive track may be formed with a width of between 2 mm and 10 mm, and preferably, with a width of 5 mm.

Preferably, said circuit board assembly comprises a laminar dielectric substrate, defining a first and second opposing planar surfaces, said laminar dielectric substrate being arrange substantially parallel to a planar surface of said power socket fascia. By arranging the circuit board to be parallel to the power socket fascia provides an advantage of further maximising the internal space of the socket box, particularly its depth Preferably, said processor is located on said first planar surface, and a ground element being formed on said second planar surface to provide a ground plane in respect of said processor.

Preferably, said conductive track is formed on said first planar surface of said laminar dielectric substrate.

The coupling elements of each power socket may comprise a live element, a neutral element, and an earth element, each coupled respectively to a corresponding AC line of said power-line Preferably, the live elements of the power sockets are coupled to each other via a first said at least one power bus, and further coupled to an AC live line of said power-line.

Preferably, the neutral elements of the power sockets are coupled to each other via a second said at least one power bus, and further coupled to an AC neutral line of said power-line.

Preferably, the earth elements of the power sockets are coupled to said ground element of said laminar dielectric substrate, and further coupled to an AC earth line of said power-line.

Optionally, said circuit board assembly further comprises a power converter for converting the AC power supply to a DC power supply for supplying voltage to at least said processor of said circuit board assembly.

The power-line may include an AC power supply line comprising a live line, a neutral line, and an earth line, for supplying AC power to said plurality of sockets.

In a second aspect, the present invention provides a power socket fascia arranged to be fitted to a power socket box, comprising: a plurality of power sockets, each power socket arranged to receive a plug of an electrical device and including coupling elements for electrically coupling said power socket to a power-line; at least one signal port for transmission and/or reception of a signal; a processor coupled to said at least one signal port and arranged to be electrically coupled to said power-line and arranged to transfer a signal between said at least one signal port and said power-line so that said signal can be transmitted and/or received from said power-line; a circuit board assembly comprising a plurality of filters, each configured to filter interfering signals occurring in the vicinity of said plurality of power sockets.

The provision of a filter at each socket is advantageous because it allows electromagnetic interference to be significantly reduced, thereby allowing the processor to operate in its maximum performance Preferably, each of said plurality of filters includes a filter circuit formed between said power line and at least two of said coupling elements of each power socket.

Preferably, said coupling elements of each power socket comprises a live element, a neutral element, and an earth element, each coupled respectively to a corresponding AC line of said power-line.

Preferably, each filter circuit comprises a first inductor coupled between said live element and a corresponding AC live line, a second inductor coupled between said neutral line and a corresponding AC neutral line, and capacitor coupled between said live element and said neutral element.

Preferably, each of said plurality of filters is configured to filter electromagnetic interference from an electrical device plugged in at least one of remaining said plurality of power sockets.

The power-line may include an AC power supply line comprising an AC live line, an AC neutral line, and an AC earth line, for supplying AC power to said plurality of power sockets.

Preferably, said circuit board assembly comprising a laminar dielectric substrate, defining a first and second opposing planar surfaces, said laminar dielectric substrate being arrange substantially parallel to a planar surface of said power socket fascia.

Preferably, said plurality of filters is located on said first planar surface, and a ground element being formed on said second planar surface to provide a ground plane in respect of said filter.

Preferably, said processor is located on said first planar surface.

In a third aspect, the present invention provides a power socket fascia arranged to be fitted to a power socket box, comprising: a plurality of power sockets, each power socket arranged to receive a plug of an electrical device and each power socket including coupling elements; at least one signal port for transmission and/or reception of a signal; and a circuit board assembly comprising: a processor coupled to said at least one signal port and arranged to be electrically coupled to said power-line and arranged to transfer a signal between said at least one signal port and said power-line so that said signal can be transmitted and/or received from said power-line; at least one power bus through which one of the coupling elements of one of said plurality of power sockets is coupled to a corresponding coupling element of at least one other said plurality of power sockets, and wherein said power bus is further arranged to be electrically coupled to the power-line; and a plurality of filters, each configured to filter interfering signals occurring in the vicinity of said plurality of power sockets.

Brief Description of the Drawings

The present invention is illustrated by way of example, and not by limitation, in the figures of the accompany drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein: Figure 1 is a rear view of the inside of a prior art power socket fascia; Figure 2 illustrates a perspective view of a power socket fascia according to an embodiment of the present invention; Figure 3 illustrates a schematic diagram of the circuitry of the power socket fascia when coupled to a power-line according to the embodiment of the present invention shown in Figure 1; Figure 4 is a rear view of the inside of a power socket fascia according to an embodiment of the present invention; Figure 5 is a side view of the inside of a power socket fascia according to an embodiment of the present invention, Figure 6 illustrates a schematic diagram of the circuitry of a power socket fascia provided with a filter circuit according to an embodiment of the present invention; and Figure 7 illustrates a schematic diagram of the circuitry of the power socket fascia provided with a filter circuit according to the embodiment of the present invention.

Detailed Description

The present invention will be described in further detail on the basis of the attached diagrams.

In the following description, a number of specific details are presented in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to a person skilled in the art that these specific details need not be employed to practice the present invention.

Figure 2 illustrates a double-gang power sockets fascia 10, which comprises two sockets 11a, 11b, each having apertures 12a, 14a, 16a (and 12b, 14b, 16b) associated with female terminals for receiving the pins of an electrical plug. The fascia 10 further comprises switches 18a, 18b for controlling the supply of electricity to the terminals of the respective sockets, and data ports 20a, 20b each arranged to receive a plug attached to a network cable.

In the illustrated arrangement, each of the data ports 20a, 20b is suitable for receiving an RJ45-type plug, but may be adapted to receive any type of network cable plug, or plug of a wireless terminal.

In Figure 2, the socket apertures 12a, 14a, 16a (or 12b, 14b, 16b) are shown in an arrangement suitable for receiving a standard United Kingdom electrical three-pin plug (i.e. according to British Standard (B S) 1363) but it will be evident to the person skilled in the art that the present invention may be readily adapted for use with power sockets in any country.

Further, Figure 2 illustrates a double-gang type power socket, but it should be appreciated that other multiple arrangements, i.e. triple-gang or quadruple-gang sockets, are possible Figure 3 illustrates the internal circuitry of the power socket fascia 10 schematically.

As can be seen, a power-line cable 22 (e.g. of a household "ring-circuit") which contains an earth line 24, a live (phase) line 26, and a neutral line 28, is coupled to connecting terminals 29a, 29b, 29c of the power socket fascia 10 Contacts 120a, 140a, 160a of a power element 30a correspond to the socket apertures 12a, 14a, 16a of socket lla in Figure 2 for receiving the pins of an electric plug. Thus, when a plug is inserted into the socket lla of the power fascia 10, a pin inserted into terminal 1 2a will make electrical contact with contact 120a, a pin inserted into terminal 14a will make contact with contact 140a, and a pin inserted into terminal 16a will make contact with contact 160a. This arrangement is well known in the art of coupling a power socket fascia to a power-line. Similarly, Contacts 120b, 140b, 160b of a power element 30b correspond to the socket apertures 12b, 14b, 16b of socket 1lb in Figure 2 Contact terminal 140a is coupled to contact terminal 140b via a power bus 154 which in turn is coupled to connecting terminal 29b Similarly, contact terminal 160a is coupled to contact terminal 160b via a power bus 156 which is in turn coupled to connecting terminal 29c.

As will be described in further detail in the forthcoming paragraphs, the power buses 154, 156 are conductive tracks printed on a planar surface of a printed circuit board (PCB) 35. An opposing surface of the PCB 35 provides a ground plane (not shown) in respect of circuits provided on the planar surface of the PCB 35.

In this example, contact terminals 120a, 120b are connected directly to the earth line 24. In an alternative arrangements, contact terminals 120a, 120b may be connected to connecting terminal 29a, either via a common ground, such as for example the ground plane (not shown) of the PCB, or directly to an earthed metal surface of a wall box (not shown) in which the double-gang power sockets fascia is installed.

In addition to the standard arrangement to provide power to the power socket fascia, the power socket fascia is also provided with a data processor 32 located on a surface of the PCB 35.

The operation of the data processor 32 will be briefly described.

The data processor 32 comprises various elements, namely: a power-line interface 36 a signal amplifier 38; a signal converter 40; and a data port interface 42.

The data processor 32 is coupled to the live (phase) and neutral lines 26, 28 of the power-line cable 22 by means of power-line interface. For clarity of the illustrating the features of the embodiment, direct connections between the power-line interface 36 and the live and neutral lines 26, 28 are not shown in the figure.

Power-line interface 36 is coupled to signal amplifier, 38 and the signal amplifier 38 is coupled to signal converter 40 In turn, signal converter 40 is coupled to data port interface 42 which, finally, is coupled to data ports 20a, 20b As stated above, the data port 20a (or 20b) is arranged to receive an RJ45-type plug attached to a Cat5 cable (or indeed any other suitable network cable) to allow a network device (e.g. a computer) to be connected for data exchange with a power socket fascia 10. A data signal transmitted by the network device (not shown) is received at the power socket fascia 10 by the data port 20a (or 20b) (shown also in Figure 2) and subsequently transferred to data port interface 42. The data signal is subsequently transferred to signal converter 40 which is arranged to convert a digital data signal into an analogue data signal. This converted analogue data signal is then transferred to signal amplifier 38 and amplified to allow for better quality transmission of the signal over the power-line. After amplification in the signal amplifier 38, the converted analogue data signal is transferred to power-line interface 36 which transfers the converted analogue data signal to the live and neutral lines 26, 28 of the power-line 22.

A different network device situated at a different location is able to receive the data signal uploaded to the power-line 22 from the first network device by way of another power socket fascia 10, similar the one described in the paragraph above, and which is connected to the same power circuitry as the first power socket. In this second power socket fascia, the power-line interface 36 is arranged to extract the analogue data signal from live and neutral lines 26, 28 and transfer this data signal to signal amplifier 38 for amplification. In an example, the signal amplifier 38 determines if a data signal received from the power-line has amplitude above a predetermined threshold. If this is the case, amplification is not necessary prior to transfer to the network device, but if the signal amplitude is below the predetermined threshold amplification of the data signal occurs.

After processing by the signal amplifier 38, the received data signal is transferred to signal converter 40 for conversion to a digital data signal The converted digital data signal is subsequently transferred to data port interface 42 which then transfers the converted digital data signal to data port 20a (or 20b) for onward transmission to the second network device.

As shown in Figure 3, a power converter 37 may optionally be provided and located on a same surface of the PCB. The power converter 37 is coupled to the live (phase) and neutral lines 26, 28 to receive AC power from the power-line. The power converter 37 then converts the AC power to a suitable DC voltage for supplying power to the data processor 32. It would be appreciated by the skilled person that other means of supplying DC power to the processor may be implemented. Furthermore, the power converter 37 may not be implemented on the same circuit board as the processor.

Of course, and as stated previously, the present invention is easily adaptable to suit power socket fascias in countries other than the UK and so an earth line 24 (and corresponding earth pin terminal) may not always be required.

Figure 4 and Figure 5 illustrate the physical layout of the internal components of a power socket fascia 200 according to an embodiment of the present invention. Figure 4 shows the rear view of the inside the power socket fascia 200, and Figure 5 shows a side view of the inside of the power socket fascia 200.

As described in the above paragraphs, in a traditional socket fascia there is a set of bars that join the live, neutral and earth connections in a circuit. The wiring connections are then placed into the centre of the socket which when in place constitutes the centre of the wall box.

In the present embodiment, the internal physical layout has been changed in order to maximise the internal space the power socket fascia 200. In particular, the present embodiment does not require usage of bulky metal bars to join the live, neutral and earth connections.

As shown in Figure 4, a printed circuit board (PCB) 280 is provided over the sockets 220a, 222b. The PCB 280 is metallised on both its planar surfaces. A front surface of the PCB 280 is shown in Figure 4, and includes a data processor 282 mounted thereon, a live power bus 242c, and a neutral power bus 262c. It would be appreciated by the person skilled in the art that other components may be provided on the front surface of the PCB 280. However, for simplicity and clarity of the description of the invention, only a minimum number of components are illustrated and described. Further, the functional features of the data processor have been described in detailed above with reference to Figure 3, and therefore will not be repeated The PCB 280 also includes a ground plane (not shown) printed on a back surface of the PCB 280. The PCB 280 is a standard FR4 PCB, although it would be appreciated that it could be made of other materials suitable for forming circuit tracks and mounting circuit components, such as a data processor.

The live power bus 242c and the neutral power bus 262c are conductive tracks formed on the front surface of the PCB 280. In this example, the width of each of the conductive track is 5 mm. However, the skilled person in the art would appreciate that the width of the conductive track could be any dimension that is suitable for transmission of AC power. For example, the width of the conductive track may be between 2 mm and 10 mm. In this example, the thickness conductive track is 0.2 mm. However, the skilled person would appreciate that other suitable thickness may also be implemented.

The substitution of large metal bars with printed conductive tracks on a PCB provides more internal space in the power socket fascia. This is of particular advantage where the available internal space of a power socket fascia is limited for installation of power-line devices. Another advantage of implementing the power bus on a PCB is that heat generated by the internal components of the power socket fascia can be dissipated more efficiently through the PCB.

Two opposing ends of the live power bus 242c are respectively connected to a first end 244a of live connecting element 242a and a first end of live connecting element 242b. In this example, the live connecting elements 242a, 242b may be any electrical conductive means, such as cables or copper strips, that are suitable for conveying AC power. Similarly, two opposing ends of the neutral power bus 262c are respectively connected to a first end 264a of neutral connecting element 242a, and a first end of neutral connecting element 242b. Similarly, the neutral connecting elements 242a, 242b include wires or copper strips that are suitable for conveying AC power. In the illustrated example, copper strips of approximately 2 mm in width are used as the connecting elements. IL)

The second ends of the live connecting elements 242a, 242b are respectively connected to connecting terminals 240a, 240b and are connected to the live line of a power cable (not shown) Similarly, the second ends of the neutral connecting elements 262a, 262b are respectively connected to connecting terminals 260a, 260b and are connected to the neutral line of a power cable (not shown).

In an alternative arrangement, and depending, for example, on the area of the front surface of the PCB 280, the live connecting elements 242a, 242b and/or the neutral connecting elements 262a, 262b can be provided directly as printed conductive tracks on the front surface of the PCB 280. This provides an advantage of reducing the number of wires, and therefore further maximises the internal space of the power socket fascia 200 and also ease the assembly process.

Although a rectangular shaped PCB is illustrated, the skilled person would appreciate that any shape or size suitable for fitting within the internal space of the power socket fascia could be utilised As shown in Figure 5, the live connecting elements 242a, 242b are respectively in connection with live terminals (not shown) of the sockets 220a, 220b via connecting elements 246a, 246b. The neutral connecting elements 262a, 262b are respectively in connection with neutral terminals (not shown) of the sockets 220a, 220b via connecting elements 266a, 266b. The connecting elements 246a, 246b, 266a, 266b may include conductive pins or wires that are capable of establishing electrical connections between the connecting elements 242a, 242b, 262a, 262b and the corresponding terminals of the sockets 220a, 220b. The connecting elements (for example, 220a and 246a) can be physically connected to each other by, for example, soldering the elements at the point of contact.

It is illustrated in Figure 5 that electrical connections between the live connecting elements 242a, 2426 and the power bus 242c (see Figure 4) are established on the front surface of the PCB 280. In contrast, electrical connections between the neutral connecting elements 262a, 262b and the power bus 262c (see Figure 4) are established from the back surface of the PCB 280 through conductive via holes 270a, 270b. It is noted that in an alternative arrangement, the electrical connections between the neutral connecting elements 262a, 2621) and the power bus 262c could also be established directly on the front surface of the PCB 280.

Figure 6 illustrates the internal circuitry of a socket of the power socket fascia 10 schematically. For simplicity, only one socket is illustrated in this example As shown in Figure 6, a power-line cable 22 which contains an earth line 24, a live (phase) line 26, and a neutral line 28, is coupled to terminals 29a, 29b, 29c of a power element 30 of the power socket fascia 10. That is, the power element 30 of the power socket fascia 10 is electrically connected to the power-line cable 22 by way of terminal 29a connecting to earth line 24, terminal 29b connecting to live (phase) line 26, and terminal 29c connecting to neutral line 28. Terminals 29a, 29b, 29c are coupled to contacts 120, 140 and 160 respectively, and these contacts 120, 140, 160 correspond to the socket apertures 12, 14, 16 (see Figure 1) for receiving the pins of an electric plug. Thus, when a plug is inserted into the power socket fascia 10, a pin inserted into terminal 12 will make electrical contact with contact 120, a pin inserted into terminal 14 will make contact with contact 140 and a pin inserted into terminal 16 will make contact with contact 160.

As can be seen, the power socket fascia 10 is provided with a filter circuit 33 on a circuit board 31. The filter circuit 33 comprises two inductors Li and L2, and a capacitor Cl. The inductors may be choke inductors, each taking a value of 2.2p11. As shown in Figure 6, contact 160 is coupled to inductor Li which is in turn coupled to the neutral line at terminals 29c. Similarly, contact 140 is coupled to inductor L2 which is in turn coupled to the live line 28 at terminals 29b. The capacitor Cl is provided between terminals 140 and 160, and it takes a value of 100nF. In an alternative arrangement, the components of the filter circuit may be implemented directly on the terminals of socket, without the use of a circuit board.

It is noted that EMI typically occurs either symmetrically or asymmetrically on an AC line. As symmetric interference can be envisioned as a source connected between a live line and a neutral line. Therefore, a "line-to-line" capacitor implemented between the live line and the neutral line could effectively remove any symmetric interference. On the other hand, asymmetric interference is represented by a source between the live (or neutral) line and the ground. Thus, the provision of inductors at the live and neutral terminals of the socket would effectively reduce such interference.

It is appreciated that the values of the components of the filter circuit 33 can be selected such that the filter circuit 33 effectively filters any unwanted electromagnetic interference (EMI) in the vicinity of the socket Thus, the skilled person would appreciate that the values of the components are not limited to those described in the above example.

In an embodiment of the present invention, the filter circuit 33 is provided in the double-gang power socket fascia described above with reference to Figure 3. The filter circuit may be provided directly on the front surface of the PCB 35 together with the data processor 32, and the power buses. This arrangement is illustrated schematically in Figure 7.

As shown in Figure 7, filter circuits 170, 172 are implemented on PCB 32 of the power socket fascia 10. The filter circuit 170 comprises two inductors 171 and 173, and a capacitor 181. As shown in the figure, contact 160a is coupled to inductor 171, and contact 160b is coupled to inductor 175. The inductors 171 and 175 are in turn coupled to power bus 156 which is coupled to connecting terminal 29c. The capacitor 181 is located between terminals 140a and 160a. Similarly, contact 140a is coupled to inductor 173, and contact 140b is coupled to inductor 177. The inductors 173 and 177 are in turn coupled to power bus 154 which is coupled to connecting terminal 29b. The capacitor 183 is located between terminals 140b and 160b.

It will be appreciated by those already skilled in the art that the present invention can be embodied in other specific forms without departing from the essential character thereof The presently-disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalents therefore are intended to be embraced therein.