AU715499B2

AU715499B2 - Decoupling unit for overvoltage protection device

Info

Publication number: AU715499B2
Application number: AU20096/97A
Authority: AU
Inventors: Ing. Karl Suchentrunk
Original assignee: Felten and Guilleaume Austria AG
Current assignee: Felten and Guilleaume Austria AG
Priority date: 1996-05-07
Filing date: 1997-05-07
Publication date: 2000-02-03
Anticipated expiration: 2017-05-07
Also published as: SK284784B6; AT404650B; ATA81296A; EP0806826B1; PL319847A1; GR970300051T1; HU221493B; AU2009697A; ATE237190T1; HUP9700819A3; CZ293858B6; HU9700819D0; SK58197A3; CZ137497A3; PL188063B1; EP0806826A2; ES2109912T1; EP0806826A3; HUP9700819A2; DE59709740D1

Abstract

The decoupling element has first and second tapping elements (1,2) and first (E1) and pref. at least second (4) decoupling components . At least all the first type of decoupling components are mounted in a common housing. The outermost connectors of the upper and lower rows of connectors in the housing are connected together electrically. The one or more decoupling elements of the second type are mounted in the same housing with the first decoupling element.

Description

Our Ref: 638689 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Felten Guilleaume Austria AG Eugenia 1 A-3943 Schrems

AUSTRIA

DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Address for Service: Invention Title: Decoupling unit for overvoltage protection device The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 P:\WPDOCS\NRC\SPECIE\638689. 19/11199 -1- Description Decoupling unit for overvoltage protection circuit The invention is directed to a decoupling unit for an overvoltage protection circuit which can be installed in control cabinets, comprising first and second arrester elements as well as decoupling components. For the protection of mains connections, two arrester elements per phase are often connected in parallel and decoupled from each other. The public three-phase system has three active conductors, all of which, as well as the neutral conductor, are to be protected in relation to the protective conductor, and in relation to one another against overvoltages. This inevitably results in a relatively large number of components four separate protective devices.

Furthermore, overvoltage protection devices are customarily the first to be arranged in the 15 system supply lines, thus resulting in wiring of larger cross section which is therefore difficult to manipulate.

The two given factors a large number of requisite elements, and wiring which is difficult to manipulate together result in time-consuming and badly configured wiring.

The present invention seeks to propose a design of decoupling components, whereby an overvoltage protection device can be arranged in a control cabinet following a particularly clear method, thus making the wiring task easy.

In accordance with the invention, this is achieved by at least all the first decoupling components being arranged in a common casing, and the outermost connecting terminals of the upper and the lower row of terminals of this casing respectively are electrically interconnected.

Through the use of a decoupling unit designed in this manner, the component expenditure is substantially reduced, and the electrical connection of the connecting terminals mentioned above P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -2render several leads, which are difficult to install, superfluous.

A further development of the invention proposes that at least one second decoupling component is arranged in a common casing with the first decoupling component.

Thereby all decoupling components are combined in a single casing, which results in a further simplification of the circuitry.

One embodiment of the invention proposes that the first connections, as well as the second connections, of the first decoupling components are run to connecting terminals located in the upper row of terminals of the common casing.

All leads required for the subsequent connections of the decoupling components can thus be installed exclusively in a position above the decoupling unit, leading to a methodical and easily 15 practicable wiring task.

.0 •In accordance with another embodiment of the invention, it is proposed that the first connections :*of the first decoupling component are run to plugs arranged in the front wall of the casing, and the second connections of the first decoupling component are run to connecting terminals 20 positioned in the upper row of terminals.

Thus the first connections of the decoupling components can be made by means of connectors being run along the front wall of the casing, a method which leads to a further simplification of the wiring.

It can further be envisaged that the first connections of the first decoupling components are, additionally, also run to connecting terminals situated in the lower row of terminals.

This design allows for a parallel connection of several decoupling units with minimum wiring, whereby the nominal current of the overvoltage protection device can be increased in a p:\WPDOCS\NRC\SPECIE\638689. 1911/99 -3straightforward manner.

An especially preferred embodiment of the invention proposes that the decoupling components be in the form of coils, and such components can be easily produced in the power range required for this application.

In this context, a further development of the invention proposes that at least one second decoupling component is in the form of a closed coil, preferably an inductive ring, such as a ferrite ring, and that all operating current-carrying conductors are run through this coil.

By this method, the component input is reduced, and thus the cost of production, and the functional reliability of the decoupling unit, is increased.

Furthermore, the invention seeks to propose a configuration of components of an overvoltage 15 protection device in a control cabinet, whereby between each phase conductor and the neutral :conductor, and between each phase conductor and the protective conductor, as well as, preferably, also between the neutral conductor and the protective conductor respectively two overvoltage arrester elements, decoupled from each other, are connected, and which are combined in a decoupling unit as described above. The wiring of this configuration can be S: 20 performed with minimum effort and in a methodical manner.

3 9..

S• In accordance with the invention, this is achieved by all the first arrester elements and all the second arrester elements being arranged immediately adjacent to one another, combined in groups, and the decoupling unit being arranged between the groups of the first and the second arrester elements.

It is hereby achieved that all conductors, those of the supply leads and of the shunt leads, can be connected to the protective device from above, a method which contributes significantly to a methodical wiring. Through the configuration of the individual components in accordance with the invention, these can be interconnected by means of standard assembly P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -4systems, which results in an easy and speedy installation.

In accordance with a preferred embodiment of the invention, it is proposed that the first connections of the first decoupling components be connected by means of connectors run along the front wall of the casings of arrester elements and decoupling units.

Plug connections are substantially faster to install than screw connections; thus, by using this method, a further simplification of the installation can be achieved. In this context, a further development of the invention is proposed, namely for at least one second decoupling component to be arranged within the connector. This results in free space being created in the casing of the decoupling unit, and enabling the first decoupling component to be constructed geometrically larger, therefore being rendered more efficient.

In accordance with a preferred embodiment of the invention, it is proposed that the 15 decoupling unit and the first arrester elements form a single component, which offers the oo o advantage of rendering some connections, which would otherwise have to be made externally, superfluous.

In this context it can further be envisaged that all first arrester elements, the decoupling unit 20 and connector can be designed as a single component.

This allows permanently installed wiring to be substituted for the connectors, resulting in Soolower transition resistances between the individual circuit components. It can be advantageous that the first arrester element is in the form of arc interrupters, such as air, gas or vacuum spark gaps or the like, as such elements are able to discharge relatively large amounts of energy without suffering damage.

Further, in this context, it can be of advantage that the second arrester elements are in the form of varistors, suppressor diodes or the like.

P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 Such components reduce an overvoltage to a relatively small magnitude, resulting in sufficient protection for all subsequent connections of users.

The present invention according to one aspect seeks to provide a decoupling unit for overvoltage protection circuits for installation in control cabinets, comprising first and second arrester elements as well as first decoupling components having first and second connections, characterised in that at least all first decoupling components are arranged in a common casing, comprising a front wall and connecting terminals being arranged in two rows being positioned adjacent the upper respectively adjacent the under lateral edge of said front wall and that the first and the last connecting terminals of each rows of connecting terminals are short-circuited.

In another preferred form of the invention it is sought to provide a decoupling unit, characterised in that the overvoltage protection circuit further comprises at least one second decoupling component, which is arranged in the common casing of the first decoupling components.

The present invention according to another aspect seeks to provide a decoupling unit, 9 characterised in that the first as well as the second connections of the first decoupling components are run to connecting terminals situated in the upper row of terminals of the common casing.

S: In another preferred form of the present invention it is sought to provide a decoupling unit, characterised in that the first connections of the first decoupling components are run to plugs 9 arranged in the front wall of the casing and the second connections of the first decoupling components are run to connecting terminals situated in the upper row of terminals.

The present invention according to yet another aspect seeks to provide a decoupling unit, characterised in that the first connections of the first decoupling components are, in addition, also run to connecting terminals situated in the lower row of terminals.

The present invention according to yet another aspect seeks to provide a decoupling unit, P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -6characterised in that the first decoupling components are in the form of coils.

The present invention according to yet another aspect seeks to provide a decoupling unit, characterised in that at least one second decoupling component is formed by a closed coil, preferably an inductive ring, such as a ferrite ring, through which coil all operating currentcarrying conductors are run.

In a broad form, the present invention seeks to provide an overvoltage protection circuit in a control box being used to protect a three phase mains system comprising three phase conductors, one neutral conductor and one protective conductor, whereby between each phase conductor and the neutral conductor and between each phase conductor and the protective conductor as well as preferably also between the neutral conductor and the protective conductor respectively a first and a second overvoltage arrester elements, decoupled from each other, are connected, and a decoupling unit for example a decoupling unit being in accordance 15 with a decoupling unit hereinbefore disclosed is provided characterised in that all first arrester elements and all second arrester elements are arranged immediately adjacent to one another and a.

combined in respective groups, and that the decoupling unit is arranged between the groups of the first and the second arrester elements.

20 Preferably, the present invention provides a circuit comprising a decoupling unit in accordance with claim 3, characterised in that the first connections of the first decoupling components can be made by a connector run along the front walls of the casing of the arrester elements and decoupling unit.

The present invention according to yet another aspect seeks to provide a circuit characterised in that at least one second decoupling element is arranged within the connector.

In accordance with a specific embodiment of the present invention there is provided a circuit characterised in that all first arrester elements together with the decoupling unit form a single component.

P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -7- In a further embodiment of the present invention there is provided a circuit characterised in that all first arrester elements, decoupling unit and connector form a single component.

The present invention according to yet another aspect seeks to provide a circuit characterised in that the first arrester elements are in the form of arc gaps, such as air, gas or vacuum spark gaps or the like.

The present invention according to yet another aspect seeks to provide a circuit characterised in that the second arrester elements are in the form of varistors, suppressor diodes or the like.

In another preferred form of the invention there is provided a decoupling unit substantially as hereinbefore described with reference to the drawings.

0** The invention is described in more detail by reference to the drawings. The drawings show 15 Fig. 1 a schematic diagram of an overvoltage protection device; 00..

Figs. 2 a, b two alternatives for an embodiment of the proposal outlined in Fig. 1 in a three- Sphase current system; Fig. 3 a front view of a protective device installed in a control cabinet as per Fig. 2 a; °,Fig. 4 a front view of a configuration in accordance with the invention of the protective device 20 as per Fig. 2b in a control cabinet.

a SFig. 5 a simplification of the configuration in Fig. 4; Figs. 6 a, b a side view of the decoupling unit, in accordance with the invention; 0 Fig. 7 two decoupling units connected in parallel and Figs. 8 a, b 12 a, b circuit diagrams for overvoltage protection devices in different network systems, and their embodiment by means of a decoupling unit, in accordance with the invention.

A variety of components are known for the protection of electrical connections against intolerably high overvoltages, such as can occur with a direct or indirect lightning stroke The most important of these are arc gaps, varistors and suppressor diodes. They vary from P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -8one another in their electrical functions, which must therefore be taken into consideration when making the selection.

For instance, arc interrupters can discharge particularly energy-rich overvoltages; however, they have the disadvantage of having relatively high residual voltage the voltage to which the overvoltage is reduced).

By contrast, varistors and suppressor diodes have a comparatively low residual voltage, but only a small discharge capacity.

In order to be able to utilise the positive functions of both types of overvoltage arrester elements simultaneously, these are connected in parallel, that is to say staggered, one behind the others as shown in the corresponding schematic diagram in Fig. 1.

o: 15 The arrester element 1, which shows the greater discharge capacity, is connected closer to the supply line in order to form "rough protection" in that area. This component discharges ea most of the overvoltage energy, substantially reducing the overvoltage, however in most cases not sufficiently.

20 The voltage still remaining after the "rough protection" is further reduced by another arrester element 2, the "''fine protection" component. After most of the overvoltage energy has a already been discharged by the "rough protection", the voltage reduction performed by the "fine protection is now accompanied only by a relatively small energy discharge. The "fine protection" should therefore, in essence, have a lower residual voltage than the "rough protection"; a particularly high discharge capacity is no longer required.

As a rule, the staggering of overvoltage arrester elements is always executed in a manner in which they are connected in series, relative to the magnitude of their residual voltages.

In the case of such staggering, it must, however, be taken into consideration that the response P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -9voltages of the arrester elements 1, 2 employed also vary from each other. An arrester element with lower residual voltage, as a rule also has a lower response voltage, so that when the overvoltage occurs, the "weak" component (fine protection) always responds first and therewith reduces the overvoltage below the response voltage of the "rough protection".

In order to avoid this problem, the arrester elements 1,2 are decoupled from each other, which is achieved by series connection of the decoupling components El, E2 to the "weaker" arrester element 2. The decoupling components El,E2 can be in the form of coils, capaciton or resistors and cause an additional voltage drop in the branch of the 'weaker component", whereby the response voltage of the "fine protection" branch is increased.

In the event that a three-phase current connection is to be protected with such an overvoltage *P 9 9 protection device, an arrangement as per Fig. 2a can for instance be proposed. In this case, between each phase conductor L1, L2, L3 and the neutral conductor N, as well as between 15 the neutral conductor N and protective conductor PE respectively, a separate protective device is to be installed.

99 9 The second decoupling component, shown as E2 in Fig. 1, between the phase conductor and I* 0.

the neutral conductor are in this case not designed as separate series components. The 0 20 resulting voltage drop is produced by the first decoupling components El, which are 9 accordingly dimensioned larger, or, in the case of coils, with greater inductivity. The latter arrangement leads to a complicated configuration whose wiring in the control cabinet is time and material consuming (compare Fig. 3).

An essential disadvantage is that the phase conductors L1, L2, L3, as well as the protective conductor PE, of the supply lead must be connected from above, whilst the neutral conductor N by contrast must be connected from below. The same problem arises with regard to the subsequent connections leading to the users; the phase conductor, as well as the protective conductor, can be tapped off the upper rows of terminals, but the neutral conductor must be tapped off the lower row of terminals and run on from there.

P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 In electrical installations, it is however desirable to be able to make all connections of supply leads and shunt leads of a configuration of equipment at its upper row of terminals, and merely distribute the necessary electrical connection within the arrangement to the upper and the lower rows of terminals.

In the circuitry as per Fig. 2b the decoupling component E2 arranged in the neutral conductor N in Fig. 2 a is not envisaged. Its electrical function is performed by a current-compensated coil 4. This coil 4 is closed, and in its simplest version is in the form of an inductive ring, for instance a ferrite ring. All operating current-carrying conductors in the case of a threephase current system these are L I, L2, L3 and N are run through this coil 4.

From an electro-technical perspective, such a coil 4 has the same effect as series inductances which are connected in a star-shape to the protective conductor PE. Thus, this coil, for currents flowing from one of the conductors L1, L2, L3 or N to the protective conductor PE, 15 causes a voltage drop and thus has a decoupling effect. Thereby the effect of the first *decoupling element E 1 is strengthened so that the function of the missing decoupling component E2 is partially or totally performed by coil 4, and the first decoupling component E 1 can therefore be dimensioned correspondingly smaller.

4444 20 An essential advantage of such a current-compensated coil 4 is that it has no effect under nonfault conditions, and therefore does not cause any losses by contrast thereto, during normal operations reactive power is taken up by series inductances.

In accordance with the invention, the configuration of components of an overvoltage protection device in the control cabinet is undertaken as per Fig. 4. This configuration is an embodiment of the schematic diagram shown in Fig. 2b. All first arrester elements 1 and all second arrester elements 2 are arranged, combined in groups, immediately adjacent to one other. Positioned between these two groups is the core component of the configuration, the decoupling unit 3. This combines at least all the first decoupling components El in one common casing. In the embodiment shown in Fig. 4, the second decoupling component 4, in P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -11the form of a current compensated coil, is also arranged in the common casing. The first decoupling components El are as is shown in Fig. 2 b arranged in series between supply and shunt leads and is preferably in the form of coils, however, as an alternative, they could also be in the form of resistors or capacitors.

The second essential construction detail of the decoupling unit 3 is the electrical connection executed within the casing interior, of the outermost connecting terminals 6, 7, 8, 9 of the upper and the lower row of terminals.

The use of the decoupling unit 3 formed in the described manner, results, as is seen in the drawing, in a particularly simple and methodical wiring of the entire overvoltage protection device.

In the event of the casings of the individual components being made according to a standard S 15 width in electrical installations, in this context, one refers to "standard units" (Teilungseinheiten); each casing has a width which is an integer multiple of a standard unit the few remaining connections, which are to be made externally, are easily designed so that standard connecting systems 10, 100 and also standard connecting bridges 11 can be used, so that the wiring tasks are essentially reduced to the tightening of several terminal screws.

Furthermore, all supply and shunt lines are connected to the upper rows of terminals.

The embodiment shown in Fig. 4 where the first, as well as the second, connections of the *o first decoupling components El are run to connecting terminals in the upper row of terminals, can be simplified by designing it in the manner as shown in Fig. 5. In this case, the first connections of the first decoupling components El are led to plugs 12, arranged at the front wall of the casing, and the second connections of the first decoupling component El to connecting terminals in the upper row of terminals.

Also, the casings of the first arrester elements 1 arranged in the phase conductors L1, L2, L3 have plugs 13 at their front walls, these plugs being connected to the phase conductors L1, P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 12- L2, L3 of the supply line. This allows for the substitution of the connection 10 in Fig. 4, which must be installed manually, with a connector 31, which is located along the front walls of the casing (compare Fig. 6a). In this case, the decoupling unit 3 can be narrower on the one hand, and on the other hand, further connections, which would have to be installed manually, are superfluous.

Since the coil 4 forming the second decoupling component E2 is relatively small, it can, as is proposed in Fig. 6b, be arranged within the connector 31. A prerequisite is naturally that at least a section of the electrical connection 5 of the connecting terminals 6, 7, 8, 9 of the neutral conductor are also run within the connector 31, so that the lead 5 is surrounded by coil 4.

Yet another further development of the invention leads to all first arrester elements 1 and the decoupling unit 3 to be designed comprising one single component. This renders the bridge 15 10, which is to be connected externally, superfluous; if the connector 31 is also incorporated into the one-component design, it can then be replaced by wiring running through the interior of the casing.

oo°0* The first decoupling element El, through which the operating current of the supplied electrical 20 equipment flows, must be dimensioned in a manner taking into consideration the heating generated by the current flow. In order to be able to use homogenous and therefore costeffectively manufactured decoupling units 3 for different values of nominal currents, it is desirable to design these in such a way that they can be connected in parallel in an easy manner for the purpose of greater total current flow.

This allows for the embodiment of the invention shown in Fig. 7. Here, the first connections to the first decoupling components El are, additionally, also run to connecting terminals in the lower row of terminals.

30 Two, or if necessary also a plurality of decoupling units 3, are arranged one below the other, and P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 13are connected in the manner shown in the drawing. Even if this is not illustrated in a separate drawing, the embodiment of the invention shown in Fig. 4 can be further developed in the manner shown in Fig. 7, that is to say that the first connections of the first decoupling components El are run to the connecting terminals in the lower row of terminals.

In principle, all the components mentioned at the outset can be used as representing the two arrester elements 1,2. However, the preferred version is to have the first arrester elements as arc interrupters, such as for instance air, gas or vacuum spark gaps or the like, and that the second arrester elements 2 are formed by varistors, suppressor diodes or the like, where in particular a combination air spark-gap/ varistor is used.

The decoupling unit in accordance with the invention, as well as the configuration of the components of the overvoltage protection device in accordance with the invention, are- 0000 O particularly functional for practical use, because it allows for a plurality of different protective 00.0 15 devices for different network systems to be configured. This is finally shown in more detail in I Figs. 8 to 12.

0 Fig. 8 a shows the circuit diagram of a protective device for a TT system. Here the configuration in accordance with the invention, as already shown already in Fig. 5, can be used.

20 For clarity, this configuration is again illustrated in Fig. 8b.

*I O @000.. O Fig. 9a shows a circuit diagram of a TT system where an isolating switch 14 is proposed in addition to the one in Fig. 8a. The configuration, in accordance with the invention, is an 0 embodiment of this circuit diagram and is illustrated by Fig. 9b.

Fig 10 a shows an overvoltage protection device for a TN-C-S-system. The neutral conductor N and the protective conductor PE are interconnected in this case, so that no voltage difference, and therefore no overvoltage, can occur between them. This makes the arrester elements, as well as the decoupling components, between neutral conductor N and protective conductor PE, as well as the coil 4, superfluous. This has also been taken into consideration in the control box P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -14in Fig. Fig. 11 a, b finally shows the invention for a TN-S-system and Fig. 12 a, b for an IT-system.

Here two overvoltage-arrester elements 1,2, decoupled from each other, are connected between each phase conductor L1, L2, L3 and the protective conductor PE, and between neutral conductor N and protective conductor PE.

The drawings exclusively show three-phase current systems, however the invention is not restricted to such systems. The invention can also be applied to two-phase connections, consisting merely of a phase conductor, a neutral conductor and a protective conductor, for systems without a neutral conductor etc. Depending on the number of lines of the system to be protected, the number of the arrester elements and the decoupling components merely need to be varied.

000 15 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

0 0 S

S

Claims

1. Decoupling unit for overvoltage protection circuits for installation in control cabinets, comprising first and second arrester elements as well as first decoupling components having first and second connections, characterised in that at least all first decoupling components are arranged in a common casing, comprising a front wall and connecting terminals being arranged in two rows being positioned adjacent the upper respectively adjacent the under lateral edge of said front wall and that the first and the last connecting terminals of each rows of connecting terminals are short-circuited.

2. Decoupling unit in accordance with claim 1, characterised in that the overvoltage protection circuit further comprises at least one second decoupling component, which is arranged in the common casing of the first decoupling components. 15

3. Decoupling unit in accordance with claim 1 or 2, characterised in that the first as well as the second connections of the first decoupling components are run to connecting terminals situated in the upper row of terminals of the common casing. S

4. Decoupling unit in accordance with claim 1 or 2, characterised in that the first 20 connections of the first decoupling components are run to plugs arranged in the front wall of the casing and the second connections of the first decoupling components are run to connecting terminals situated in the upper row of terminals. o•

5. Decoupling unit in accordance with any one of the claims 1 to 4, characterised in that the first connections of the first decoupling components are, in addition, also run to connecting terminals situated in the lower row of terminals.

6. Decoupling unit in accordance with any one of the claims 1 to 5, characterised in that the first decoupling components are in the form of coils. P:\WPDOCS\NRC\SPECIE\638689.- 19/11/99 -16-

7. Decoupling unit in accordance with one of the claims 1 to 6, characterised in that at least one second decoupling component is formed by a closed coil, preferably an inductive ring, such as a ferrite ring, through which coil all operating current-carrying conductors are run.

8. An overvoltage protection circuit in a control box being used to protect a three phase mains system comprising three phase conductors, one neutral conductor and one protective conductor, whereby between each phase conductor and the neutral conductor and between each phase conductor and the protective conductor as well as preferably also between the neutral conductor and the protective conductor respectively a first and a second overvoltage arrester elements, decoupled from each other, are connected, and a decoupling unit for example a decoupling unit being in accordance with one of the claims 1 to 7 is provided characterised in that all first arrester elements and all second arrester elements are arranged immediately adjacent to one another and combined in 15 respective groups, and that the decoupling unit is arranged between the groups of the first and the second arrester elements. 0*

9. A circuit in accordance with claim 8 comprising a decoupling unit in accordance with claim 3, characterised in that the first connections of the first decoupling components 20 can be made by a connector run along the front walls of the casing of the arrester elements and decoupling unit. o 9

10. A circuit in accordance with claim 9, characterised in that at least one second decoupling element is arranged within the connector.

11. A circuit in accordance with any one of the claims 8, 9 or 10, characterised in that all first arrester elements together with the decoupling unit form a single component.

12. A circuit in accordance with any one of the claims 8 to 11, characterised in that all first arrester elements, decoupling unit and connector form a single component. P:\WPDOCS\NRC\SPECIE\638689. 19/11/99 -17-

13. A circuit in accordance with any one of the claims 8 to 12, characterised in that the first arrester elements are in the form of arc gaps, such as air, gas or vacuum spark gaps or the like.

14. A circuit in accordance with any one of the claims 7 to 13, characterised in that the second arrester elements are in the form of varistors, suppressor diodes or the like. A decoupling unit substantially as hereinbefore described with reference to the drawings. Dated this 8th day of October, 1999 FELTEN GUILLEAUME AG By It's Patent Attorneys

15 DAVIES COLLISON CAVE *e