WO 98/56079 PCT/GB98/00741 1 LINE PROTECTION DEVICES The present invention relates to line protection devices and more especially, but not exclusively, to electrical surge suppression devices for electrical and electronic equipment connected through power lines to a mains source of electricity. Electrical and electronic equipment such as computers can be damaged by voltage spikes and electromagnetic interference conducted through power lines. One source of electromagnetic interference is lightning strikes which generate electromagnetic fields which, in turn, induce high voltages. Other sources include fluorescent lights, air conditioning equipment. The energy transferred from these fields can damage or destroy sensitive electronic equipment, particularly sensitive solid state input circuits of computers and peripheral equipment, scanners, printers, facsimile machines and other specialised electrical and telecommunications equipment. Line protection devices are known which operate to protect sensitive electronic and telecommunications equipment from voltage spikes electrical transients and electromagnetic interference. Typically, these devices are bulky and expensive. Generally, they require a separate power plug and include a housing for the suppression circuitry connected by cabling to the plug. This cabling can be in excess of one metre in length and can impose WO 98/56079 PCT/GB98/00741 2 impedances sufficient to reduce the effectiveness of the suppression circuitry. One example of such a line protection device is disclosed in GB-A 2161659. The device is a cable unit for connecting electrical devices and includes a lengthwise extending electrically conductive screening cover and two electrically conductive housings connected by a screened cable and coarse over voltage protection means positioned in one of the housings and fine over voltage protection means positioned in the other housing, the length of the cable unit being at least one metre. Another example of a known line protection device is disclosed in GB A-2209893. The device includes at least one 2-stage protection circuit housing located with an electro-magnetically shielded enclosure in the form of a closed metal box. This box is releasably fitted to an external wall surface of an equipment cabinet so that the output socket of the line protection device communicates directly with the interior of the cabinet. Clearly, the need for enclosures, cabling and other items of hardware increases production and distribution costs, as well as imposing a space penalty on the end user. Surge suppression circuitry can also be included within the electronic equipment to be protected. This reduces the space penalty referred to above but suffers from the disadvantage that repair or replacement after a voltage surge is time consuming and expensive. EP-A-259180 discloses a different type of known circuit protection device. This device can be incorporated into a coaxial cable connector for protecting the circuit from voltage transients and includes an annulus having a central aperture for receiving a pin of the connector. The annulus is electrically insulating and has a central electrode for connection to the WO 98/56079 PCT/GB98/00741 3 connector pin and a peripheral electrode for connection to the connector housing and the coaxial cable screen. A portion of the electrodes overlap each other and are separated by a layer of semi conductor switching material which changes to a low resistance state when the cable is subjected to a voltage variant. GB-A-2274030 discloses a voltage transient limiting device which can be slipped over the male pins of an electrical plug and is thin enough to allow the plug to be positioned within a female socket without interference from the device. Both EP-A-259180 and GB-A-2274030 suffer from a number of practical disadvantages. One object of this invention is to provide a line protection device which overcomes, or at least alleviates, the disadvantages discussed above. According to the present invention in one aspect, there is provided a line protection device which comprises a single-piece module having at one of its ends a connector for connection to a male IEC connector and at its other end a connector for connection to a female IEC connector, the module having within its central section circuitry for suppressing voltage transients received from a mains source to which one or other of the IEC connectors is connected. The device may be produced as a moulding from a flame retardant plastics material. The device may include an indicator light which is illuminated when the device circuitry is active. The indicator light may be positioned in an elevated location on the module. The device may additionally or alternatively include an electrically operated audible alarm which operates in the event of WO 98/56079 PCT/GB98/00741 4 a voltage transient occurring. The alarm may automatically reset after a voltage transient has passed. The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view of a surge suppression device in accordance with the invention and a computer to be protected thereby; Figures 2 to 5 are respectively plan, side and end views of a suspension device in accordance with the invention; and Figures 6 to 9 are sectional views taken respectively along lines VI-VI, VII-VII, VIII-VIII and IX-IX of Figures 2 to 5. The device illustrated in the drawing comprises a single piece module 1 positioned in line between an IEC (International Electrotechnical Commission) power socket connected to a mains supply of electricity and an IEC plug connected to electronic equipment to be protected from voltage transients. The module 1 is typically produced as a moulding from a flame retardant plastics material. Typically, the module has a voltage rating of 230 volts (this of course being dependent on the power source to which it is to be connected), a maximum current rating of 10 amps and a maximum current surge handling of 2500 amps. Power consumption of the module is typically 0.6 watts. Typical module dimensions are length 80mm, width 37mm and depth 27mm. The weight of the module is typically 60 grams. In Figure 1, the electronic equipment is a computer 2. Other electronic and/or telecommunications equipment can also be protected, these including colour monitors of personal computers, scanners, printers, WO-98/56079 PCT/GB98/00741 5 plotters and facsimile machines. These are just examples of electrical and telecommunications equipment for which protection can be provided. The module 1 has a central section 3 which houses the necessary electrical circuitry for suppressing voltage transients. At one of its ends, the module has a male IEC plug connector 4 which, in use, is connected to pins of a female IEC socket connector 5 set in the rear of the computer 2. At its other end, the module has a female IEC socket connector 6 which receives a male IEC plug connector 7 connected by a suitable cable and plug to a mains supply. An indicator neon light 8 is provided to indicate, when lit, that the circuitry is active when the module is connected in-line between the power supply and the computer 2. If the device has been subjected to a severe surge overload which cannot be contained, the circuitry is broken and is no longer active. In this circumstance, the light switches off and the module or the light must be replaced. Before replacement, the associated equipment continues to operate normally but without surge protection. An audible alarm is also provided, this sounding in the event that the circuitry is inactive. This audible alarm may be in addition to or as an alternative to the indicator light 8. The presence of an audible alarm is preferred because in use the line protection device locates neatly behind the computer and will accordingly be rarely visible. The alarm is automatically reset after a voltage surge has passed. Alternatively, the module is replaced. Even when the line protection device is inactive, power will still be supplied to the computer 2. Turning now to Figures 2 to 9, in which integers discussed above in relation to Figure 1 have been given the same reference numerals, the central section 3 of the module 1 is raised to ensure that the indicator light is generally visible. The plug and socket connectors 4, 6 can be seen from Figures 4, 5, 8 and 9 to be of 3-pin construction; 2-pin or other configurations could, of course, be adopted.
WO 98/56079 PCT/GB98/00741 6 The voltage suppression circuitry is indicated generally by reference numeral 10 and comprises of a standard protection circuit with three metal oxide varristors 11 giving full premium three mode protection (L-N, L-E and N-E). If a significant surge is experienced the varristors 11 are sacrificed and two thermal fuses (not shown) will isolate the surge circuitry. This action in turn will activate an alarm 12 to warn the operator that the unit is no longer protecting the equipment and the unit needs to be replaced. The circuitry is mounted on a board 15 below which the alarm is positioned. The alarm operates to warn the operator that the inline surge unit needs to be replaced. The indicator light 8 is connected to the circuitry 10 via a lead 15 and remains lit while the circuitry is active. Thermal overload protection for the module is provided. In use, the modular line protection device 1 is simply connected in line between the power supply and the electrical or telecommunications equipment to be protected through conventional IEC connectors. The space taken by the modular device 1 is minimal and replacement of the device when rendered inactive by an uncontained surge overload is relatively easy. Line protection devices in accordance with this invention can be used for two or three cored products; they can additionally be employed for multi core products including data carrying cables. The devices provided protection from degradation damage and downtime, thereby increasing operator productivity. It will be appreciated that the foregoing is merely exemplary of line protection devices in accordance with this invention and that various modifications can be made without departing from the true scope of this invention as set out in the appended claims.