EP0308553A1 - Transient suppressor device assembly - Google Patents

Transient suppressor device assembly Download PDF

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Publication number
EP0308553A1
EP0308553A1 EP87308446A EP87308446A EP0308553A1 EP 0308553 A1 EP0308553 A1 EP 0308553A1 EP 87308446 A EP87308446 A EP 87308446A EP 87308446 A EP87308446 A EP 87308446A EP 0308553 A1 EP0308553 A1 EP 0308553A1
Authority
EP
European Patent Office
Prior art keywords
device assembly
transient suppressor
fail
clip
suppressor device
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP87308446A
Other languages
German (de)
French (fr)
Inventor
Christopher George Howard
Norman Doughty
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Semitron Industries Ltd
Original Assignee
Semitron Cricklade Ltd
Semitron Industries Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Semitron Cricklade Ltd, Semitron Industries Ltd filed Critical Semitron Cricklade Ltd
Priority to EP87308446A priority Critical patent/EP0308553A1/en
Priority to US07/215,301 priority patent/US4866563A/en
Priority to AU22768/88A priority patent/AU2276888A/en
Publication of EP0308553A1 publication Critical patent/EP0308553A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T1/00—Details of spark gaps
    • H01T1/14—Means structurally associated with spark gap for protecting it against overload or for disconnecting it in case of failure
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
    • H02H9/06—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage using spark-gap arresters

Definitions

  • Transient suppressor device assem­bly is known, for example, from EP-A-0 123 126. Telecommuni­cation systems are commonly protected from transient voltage surges, such as those derived from lightning, by gas discharge tubes (G.D.T.). Figure 1 shows a typical configuration where a three terminal device is placed between the two telephone lines and earth. Frequently main distribution frame systems are fit­ted with one three-terminal G.D.T. per pair of lines.
  • the G.D.T. has massive current carrying capability but it has three major disadvantages.
  • the first disadvantage is that the device is not fail-safe in the event of its overheating.
  • the application of a continuous over-current such as might be deriv­ed from a mains contact of the system, causes excessive heat­ing and serious damage to the main distribution frame.
  • Over-­temperature fail-safe devices are known from DE-A 29 11 110, EP-A-0 040 522, EP-A-0 134 718 for example.
  • degrada­tion of the parameters of the G.D.T. cannot be detected. It is possible for the DC spark-over voltage of the device to increase progressively due to a lack of device hermeticity. This problem is solved by the invention described here.
  • the device is relatively slow in its operation.
  • the increasing use of semi­conductor devices in telecommunication applications has led to situations where the G.D.T. cannot give adequate protection.
  • Semiconductor devices are extremely sensitive to overvoltage conditions and can be destroyed by voltage surges of less than a nanosecond.
  • Semiconductor protection devices have been devel­oped with faster response times than this, which solve the overvoltage problem, but are unable to cope with the huge cur­rents (of the order of 5KA) which protection devices are expect­ed to carry.
  • the invention described here shows how a small transient suppression device of similar size to a G.D.T. can be made to have fast response and high current carrying capability.
  • Figure 2 shows the G.D.T. fitted with two bidirectional avalanche diodes and thermal cut-outs.
  • the thermal cut-outs ensure that the unit fails short-circuit in the event of its overheating.
  • the short-circuit function is carried out by a spring-loaded contact which is released by the melting of a solder slug as in DE-A-2911110.
  • the bidirectional diodes are specified either to provide protection aganist an increase in G.D.T. spark-over voltage or to protect electronic components against rapidly rising transient pulses or to protect against both effects. Protection against an increase in G.D.T. spark-over voltage can be achieved by selecting diodes which have breakdown voltages considerably above those of the DC spark-over voltage of the G.D.T. and very low power ratings.
  • the G.D.T. will not respond fast enough to a rapidly rising pulse (e.g. the CCITT 5KV lightning test with 10 ⁇ sec rise time). Whilst the G.D.T. may be comfortably rated in terms of DC spark-­over voltage, response time of the order of 1 ⁇ sec can allow a large excess voltage to develop before the device switches. In­deed voltages in excess of 700V can be obtained across the ter­minals of a nominal 250 volt G.D.T. when this test is carried out.
  • Figure 3 shows an oscilloscope trace of this test, which was carried out on a T83-C250GB G.D.T. manufactured by Siemens.
  • Protection against fast-rising transient pulses can be obtained by using the circuit in Figure 2 with high power transient suppression avalanche diodes.
  • the avalanche diodes are selected to have a greater breakdown voltage than the DC spark-over volt­age of the G.D.T. and to be capable of handling the power dissipated in them prior to the switching on of the G.D.T. They must also not exceed the clamp voltage at this stage. Once the G.D.T. has triggered the voltage across the diodes falls below their breakdown voltage and they turn off. The system then behaves as a G.D.T. alone.
  • a transient suppressor device assembly according to claim 1, with circuit design as in Figure 2, provides improved fail-safe opera­tion, prevents the main distribution frame from excessive heat­ing and serious damage, provides a small transient suppression device which can be easily, speedily and cheaply manufactured and provides a device which shows robust and reliable properties.
  • the parameters of the avalanche diodes can be selected so that the unit is protected against increases in G.D.T. spark-over voltage or so that the unit provides protection against transient pulses with fast rise times. In principle, it may be possible to select diodes which carry out both functions simultaneously.
  • the electrical components of the transient suppressor device assembly are held in intimate thermal contact so that these elec­trical components are never permitted to overheat (ref. European Patent Application number 8530 6408.7).
  • the avalanche diodes in Figure 2 are selected to give protection against an increase in G.D.T. breakdown voltage.
  • the circuit is fitted with a G.D.T. whose DC spark-over voltage is in the range 280-420 volts, and 1 watt diodes whose breakdown voltages are in the range 500-800 volts.
  • the unit is intended to clamp at voltages below 1000 volts on a standard CCITT 5KA pulse with 8 ⁇ sec rise time and a time to half current decay of 20 ⁇ sec.
  • the presence of the diodes ensures that this clamp voltage is never exceeded, even in the event of an open circuit G.D.T. device. Should the G.D.T. go open circuit, the huge current through the diode will render it short-circuit.
  • the avalanche diodes of the circuit in Figure 2 are selected to protect elec­tronic components against rapidly rising pulses.
  • Figure 4 shows an oscilloscope trace of the CCITT 5KV lightning test with 10 ⁇ sec rise time.
  • the G.D.T. used for these measurements was type T83-C250GB manufactured by Siemens and this was fitted with Semi­tron diodes type L8B280C which break down at 280 volts ⁇ 5%.
  • Typical measured G.D.T. DC breakdown voltages were 240 volts.
  • the diode chip assemblies consist of passivat­ed silicon chips sandwiched between two protective electrodes.
  • Figure 7 and 8 show one assembly embodiment of the transient suppressor device assembly of Figures 5 and 6.
  • Figures 9, 11 and 12 show the clip 2 of Figures 5 to 8 in its operating position under tension.
  • the clip 2 should be under tension of approximately 1.5lbs in the X direction ( Figure 11).
  • Figure 10 shows the clip 2 of Figures 5 to 8 in the relaxed state.
  • the clip 2 may consist of stainless steel or of a beryllium-copper alloy.
  • a comparison between Figures 10 and 11 shows how part 11 of Clip 2 moves from the operating position of Figure 11 to the relaxed state pro­file of Figure 10.
  • Figures 13 and 14 show sections of another assembly embodiment of a transient suppressor device assembly in full correspondence to Figures 7 and 8. Only the geometry of the diodes 3, 4 is changed and the clip 2 is modified accordingly.
  • Figures 15 to 18 show details of a clip 2 of Figures 13 and 14.
  • Figures 15, 17 and 18 show the clip 2 of Figures 13 and 14 in its operating position under tension.
  • Figure 16 shows the clip 2 of Figures 13 and 14 in the relaxed state.
  • Figures 15 to 18 correspond fully to Figures 9 to 12.
  • the specification of the diodes 3, 4 depends on which functional embodiment of the invention is being made. They are fitted to provide protection against an increase in G.D.T. spark-over voltage or to give protection against rapidly rising pulses or to carry out both functions. If the power dissipated in the diodes 3, 4 exceeds their rating, they will go short-circuit, ensuring fail-safe operation of the unit.
  • the four functions of the clip 2 are:-

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  • Emergency Protection Circuit Devices (AREA)

Abstract

A transient suppressor device assembly comprises at least two electrical components (1, 3, 4) and a fail-safe clip (2). The fail-safe clip (2) has means for simultaneously providing the necessary electrical conductive paths, providing fail-safe operation if an electrical component (1, 3, 4) becomes over­heated and holding together the electrical components (1, 3, 4).

Description

  • This invention relates to a transient suppressor device assem­bly according to claim 1. Transient suppressor device assem­blies are known, for example, from EP-A-0 123 126. Telecommuni­cation systems are commonly protected from transient voltage surges, such as those derived from lightning, by gas discharge tubes (G.D.T.). Figure 1 shows a typical configuration where a three terminal device is placed between the two telephone lines and earth. Frequently main distribution frame systems are fit­ted with one three-terminal G.D.T. per pair of lines.
  • The G.D.T. has massive current carrying capability but it has three major disadvantages. The first disadvantage is that the device is not fail-safe in the event of its overheating. The application of a continuous over-current such as might be deriv­ed from a mains contact of the system, causes excessive heat­ing and serious damage to the main distribution frame. Over-­temperature fail-safe devices are known from DE-A 29 11 110, EP-A-0 040 522, EP-A-0 134 718 for example. Secondly, degrada­tion of the parameters of the G.D.T. cannot be detected. It is possible for the DC spark-over voltage of the device to increase progressively due to a lack of device hermeticity. This problem is solved by the invention described here. Thirdly, the device is relatively slow in its operation. The increasing use of semi­conductor devices in telecommunication applications has led to situations where the G.D.T. cannot give adequate protection. Semiconductor devices are extremely sensitive to overvoltage conditions and can be destroyed by voltage surges of less than a nanosecond. Semiconductor protection devices have been devel­oped with faster response times than this, which solve the overvoltage problem, but are unable to cope with the huge cur­rents (of the order of 5KA) which protection devices are expect­ed to carry. The invention described here shows how a small transient suppression device of similar size to a G.D.T. can be made to have fast response and high current carrying capability.
  • Figure 2 shows the G.D.T. fitted with two bidirectional avalanche diodes and thermal cut-outs. The thermal cut-outs ensure that the unit fails short-circuit in the event of its overheating. The short-circuit function is carried out by a spring-loaded contact which is released by the melting of a solder slug as in DE-A-2911110. The bidirectional diodes are specified either to provide protection aganist an increase in G.D.T. spark-over voltage or to protect electronic components against rapidly rising transient pulses or to protect against both effects. Protection against an increase in G.D.T. spark-over voltage can be achieved by selecting diodes which have breakdown voltages considerably above those of the DC spark-over voltage of the G.D.T. and very low power ratings. They normally take no part in the operation of the device. However, if the spark-over voltage of the G.D.T. increases, for instance as a result of gas leak­age from the capsule, the diodes then provide the fail-safe characteristic. A progressive degradation of G.D.T. parameters will lead firstly to the diodes clamping during surges and then to their ratings being exceeded and the diodes failing short-­circuit.
  • The G.D.T. will not respond fast enough to a rapidly rising pulse (e.g. the CCITT 5KV lightning test with 10µsec rise time). Whilst the G.D.T. may be comfortably rated in terms of DC spark-­over voltage, response time of the order of 1µsec can allow a large excess voltage to develop before the device switches. In­deed voltages in excess of 700V can be obtained across the ter­minals of a nominal 250 volt G.D.T. when this test is carried out. Figure 3 shows an oscilloscope trace of this test, which was carried out on a T83-C250GB G.D.T. manufactured by Siemens. Protection against fast-rising transient pulses can be obtained by using the circuit in Figure 2 with high power transient suppression avalanche diodes. The avalanche diodes are selected to have a greater breakdown voltage than the DC spark-over volt­age of the G.D.T. and to be capable of handling the power dissipated in them prior to the switching on of the G.D.T. They must also not exceed the clamp voltage at this stage. Once the G.D.T. has triggered the voltage across the diodes falls below their breakdown voltage and they turn off. The system then behaves as a G.D.T. alone.
  • A transient suppressor device assembly according to claim 1, with circuit design as in Figure 2, provides improved fail-safe opera­tion, prevents the main distribution frame from excessive heat­ing and serious damage, provides a small transient suppression device which can be easily, speedily and cheaply manufactured and provides a device which shows robust and reliable properties. The parameters of the avalanche diodes can be selected so that the unit is protected against increases in G.D.T. spark-over voltage or so that the unit provides protection against transient pulses with fast rise times. In principle, it may be possible to select diodes which carry out both functions simultaneously.
  • The electrical components of the transient suppressor device assembly are held in intimate thermal contact so that these elec­trical components are never permitted to overheat (ref. European Patent Application number 8530 6408.7).
  • In order that the invention may be more fully understood, embod­iments thereof and their operating characteristics will be de­scribed by way of illustrative examples, reference being had to the accompanying drawings wherein:
    • Figure 1 shows a transient suppressor device accord­ing to prior art,
    • Figure 2 illustrates the principle of a transient suppressor device assembly according to the invention,
    • Figures 3 and 4 show oscilloscope traces illustrating the responses of devices of Figures 1 and 2 to rapidly rising pulses,
    • Figures 5 and 6 show a transient suppressor device assembly according to the invention,
    • Figures 7 to 12 show a first assembly embodiment, and
    • Figures 13 to 18 show a second assembly embodiment.
  • In a first functional embodiment of the invention, the avalanche diodes in Figure 2 are selected to give protection against an increase in G.D.T. breakdown voltage. The circuit is fitted with a G.D.T. whose DC spark-over voltage is in the range 280-420 volts, and 1 watt diodes whose breakdown voltages are in the range 500-800 volts. The unit is intended to clamp at voltages below 1000 volts on a standard CCITT 5KA pulse with 8µsec rise time and a time to half current decay of 20µsec. The presence of the diodes ensures that this clamp voltage is never exceeded, even in the event of an open circuit G.D.T. device. Should the G.D.T. go open circuit, the huge current through the diode will render it short-circuit.
  • In a second functional embodiment of the invention, the avalanche diodes of the circuit in Figure 2 are selected to protect elec­tronic components against rapidly rising pulses. Figure 4 shows an oscilloscope trace of the CCITT 5KV lightning test with 10µsec rise time. The G.D.T. used for these measurements was type T83-C250GB manufactured by Siemens and this was fitted with Semi­tron diodes type L8B280C which break down at 280 volts ±5%. Typical measured G.D.T. DC breakdown voltages were 240 volts.
  • These aforementioned principles have been incorporated in the design of the Semitron SL22A series of surge suppressors, por­trayed in Figure 5. A standard 3 terminal G.D.T. is fitted with a spring clip 2. This locates cylindrical avalanche diode chip assemblies 3 and 4 and solder pellets 5 and 6.
  • If, during an overload the solder melts, the spring 2 moves so that it contacts the G.D.T. electrode at 7, 8, 9 or 10, shorting the G.D.T. terminals. The diode chip assemblies consist of passivat­ed silicon chips sandwiched between two protective electrodes.
  • Figure 7 and 8 show one assembly embodiment of the transient suppressor device assembly of Figures 5 and 6. Figures 9, 11 and 12 show the clip 2 of Figures 5 to 8 in its operating position under tension. The clip 2 should be under tension of approximately 1.5lbs in the X direction (Figure 11). Figure 10 shows the clip 2 of Figures 5 to 8 in the relaxed state. The clip 2 may consist of stainless steel or of a beryllium-copper alloy. A comparison between Figures 10 and 11 shows how part 11 of Clip 2 moves from the operating position of Figure 11 to the relaxed state pro­file of Figure 10.
  • Figures 13 and 14 show sections of another assembly embodiment of a transient suppressor device assembly in full correspondence to Figures 7 and 8. Only the geometry of the diodes 3, 4 is changed and the clip 2 is modified accordingly. Figures 15 to 18 show details of a clip 2 of Figures 13 and 14. Figures 15, 17 and 18 show the clip 2 of Figures 13 and 14 in its operating position under tension. Figure 16 shows the clip 2 of Figures 13 and 14 in the relaxed state. Figures 15 to 18 correspond fully to Figures 9 to 12.
  • The specification of the diodes 3, 4 depends on which functional embodiment of the invention is being made. They are fitted to provide protection against an increase in G.D.T. spark-over voltage or to give protection against rapidly rising pulses or to carry out both functions. If the power dissipated in the diodes 3, 4 exceeds their rating, they will go short-circuit, ensuring fail-safe operation of the unit.
  • The four functions of the clip 2 are:-
    • 1. The clip 2 is the fundamental assembly element. No other components, solders or glues are required to complete the assembly of the electronic components and the over-tem­perature protection solder preforms to form the finished transient suppressor device assembly.
    • 2. The clip 2 is able to provide the necessary electrical conductive paths between the components of the unit.
    • 3. The clip allows the components of the unit to be ther­mally connected.
    • 4. The clip, in conjunction with the over-temperature pro­tection solder preforms, is able to provide fail-safe operation if any part of the unit becomes overheated.
  • The use of one single component (clip 2) to carry out all these functions is unique.

Claims (4)

1. Transient suppressor device assembly comprising at least two electrical components (1, 3, 4) characterised by a fail-safe clip (2) having means for simultaneously:
(a) providing the necessary electrical conductive paths between at least two of the electrical components (1, 3, 4);
(b) providing fail-safe operation, if at least one of the at least two electrical components (1, 3, 4) becomes overheated, and
(c) holding together at least two of the electrical com­ponents by resilience.
2. Transient suppressor device assembly according to claim 1, characterised by a gas discharge tube (G.D.T.) (1) as an elec­trical component.
3. Transient suppressor device assembly according to claim 1 or 2, characterised by a semiconductor device ( 3, 4) as an electrical component.
4. Transient suppressor device assembly according to one of the claims 1 to 3, characterised in that the fail-safe clip (2) consists of a beryllium-copper alloy.
EP87308446A 1987-09-24 1987-09-24 Transient suppressor device assembly Withdrawn EP0308553A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP87308446A EP0308553A1 (en) 1987-09-24 1987-09-24 Transient suppressor device assembly
US07/215,301 US4866563A (en) 1987-09-24 1988-07-05 Transient suppressor device assembly
AU22768/88A AU2276888A (en) 1987-09-24 1988-09-23 Transient suppressor device assembly

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP87308446A EP0308553A1 (en) 1987-09-24 1987-09-24 Transient suppressor device assembly

Publications (1)

Publication Number Publication Date
EP0308553A1 true EP0308553A1 (en) 1989-03-29

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP87308446A Withdrawn EP0308553A1 (en) 1987-09-24 1987-09-24 Transient suppressor device assembly

Country Status (3)

Country Link
US (1) US4866563A (en)
EP (1) EP0308553A1 (en)
AU (1) AU2276888A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2222023A (en) * 1988-08-10 1990-02-21 Sankosha Co Ltd Arrester apparatus
ES2133124A1 (en) * 1994-05-04 1999-08-16 Cymem S A Improvements introduced into patent of invention number P- 9400938/4, for "External short-circuit device for telephone-equipment protection modules and the like"

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US5369543A (en) * 1992-08-13 1994-11-29 Adc Telecommunications, Inc. Thyristor fail-safe device
DE4330178B4 (en) * 1993-08-31 2005-01-20 Epcos Ag Gas-filled surge arrester with copper electrodes
US5836791A (en) * 1994-10-21 1998-11-17 Psi Telecommunications, Inc. Modular telecommunications terminal block
US6266223B1 (en) 1999-06-30 2001-07-24 Tyco Electronics Corporation Line protector for a communications circuit
US6327129B1 (en) 2000-01-14 2001-12-04 Bourns, Inc. Multi-stage surge protector with switch-grade fail-short mechanism
WO2001082670A1 (en) * 2000-04-20 2001-11-01 Siemens Aktiengesellschaft Interference suppressor
DE20202579U1 (en) * 2002-02-19 2003-04-03 Ccs Technology Inc Protective device for protecting against the effects of electromagnetic fields
DE102005016848A1 (en) * 2005-04-12 2006-10-19 Epcos Ag Surge arresters
US20080165466A1 (en) * 2007-01-05 2008-07-10 Luke Timothy Gritter Method and Apparatus For Providing a Carbon Nanotube Plasma Limiter Having a Subnanosecond Response Time
DE102008022794A1 (en) * 2008-01-31 2009-08-06 Epcos Ag Electrical protection component with short-circuit device
CA2722362A1 (en) * 2008-04-25 2009-10-29 Access Business Group International Llc Input protection circuit
US9748764B2 (en) * 2015-01-06 2017-08-29 Hubbell Incorporated Surge protective devices
DE102015121438B4 (en) 2015-12-09 2023-12-28 Tdk Electronics Ag Electrical protective component with short-circuit device

Citations (4)

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EP0017337A1 (en) * 1979-03-22 1980-10-15 Reliance Electric Company Line protector for a communications circuit
EP0027061A1 (en) * 1979-10-05 1981-04-15 Citel Lightning arrester device allowing an external short-circuiting and corresponding protection assembly
WO1986000463A1 (en) * 1984-06-28 1986-01-16 Siemens Aktiengesellschaft Vacuum switch with vacuum control device
GB2172453A (en) * 1985-03-11 1986-09-17 Dubilier Beswick Div Overvoltage protection arrangements

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US4212047A (en) * 1976-08-31 1980-07-08 Tii Corporation Fail-safe/surge arrester systems
US4062054A (en) * 1976-08-31 1977-12-06 Tii Corporation Multi-function fail-safe arrangements for overvoltage gas tubes
US4303959A (en) * 1977-10-18 1981-12-01 Tii Industries, Inc. Fail safe surge arrester systems
US4326231A (en) * 1978-02-24 1982-04-20 Gerald Coren Clip-on protector
US4544983A (en) * 1983-04-28 1985-10-01 Northern Telecom Limited Overvoltage protection device
DE3323687C2 (en) * 1983-07-01 1986-12-18 Krone Gmbh, 1000 Berlin Surge arrester magazine for connection strips in telecommunications technology

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0017337A1 (en) * 1979-03-22 1980-10-15 Reliance Electric Company Line protector for a communications circuit
EP0027061A1 (en) * 1979-10-05 1981-04-15 Citel Lightning arrester device allowing an external short-circuiting and corresponding protection assembly
WO1986000463A1 (en) * 1984-06-28 1986-01-16 Siemens Aktiengesellschaft Vacuum switch with vacuum control device
GB2172453A (en) * 1985-03-11 1986-09-17 Dubilier Beswick Div Overvoltage protection arrangements

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2222023A (en) * 1988-08-10 1990-02-21 Sankosha Co Ltd Arrester apparatus
US4984125A (en) * 1988-08-10 1991-01-08 Sankosha Corporation Arrester apparatus
GB2222023B (en) * 1988-08-10 1992-10-28 Sankosha Co Ltd Arrester apparatus
ES2133124A1 (en) * 1994-05-04 1999-08-16 Cymem S A Improvements introduced into patent of invention number P- 9400938/4, for "External short-circuit device for telephone-equipment protection modules and the like"

Also Published As

Publication number Publication date
US4866563A (en) 1989-09-12
AU2276888A (en) 1989-04-06

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