DE1927007C - Method for determining electrical faults in a multi-stage switching network, in particular in a telephone exchange - Google Patents

Description

The multi-level switching network of an indirectly controlled switching system usually has wiring which are quite extensive. It is therefore not completely over with such a switching network to conclude that possibly as a result of electrical errors in the processing of Verbin Adequate requirements undesirable effects occur It is now already known that measures can be taken in order to resolve such errors as early as possible and to prevent them from becoming disruptive works. So it is B. known (see. German Patent writing 1 261 173) to build test connections each of which leads via one of the possible connecting routes. Any such test connection is then checked with the help of test equipment. Tuesday

tu i a test connection is put together after the other develop- ments, in which in Zwigstell. Allocation relays are inserted so that all possible connection routes to the connection line cores are inserted, grasp, of course a certain amount of that becomes an indirectly controlled, switching system, Time required. It can not be especially a telephone exchange, avoid having to own a newly created electrical 5 that has a connection request error only after a more or less large change in the switching network to be switched through connection period is detected and is therefore divided into partial routes beforehand, which are initially already switched through one after the other because of a connection request Connection path in the disturbing one, in which with such a partial connection Way affects. It can, for. B. Doppelverbin- 10 it is checked whether the relevant partial route fertilize or fork connections come about. an inadmissible one due to an electrical fault Fs is now already a method of avoiding potential or an impermissible current, and Incorrect settings are only made for comparable items, on the other hand, when the entire connection path is only used known directions through which double connections are switched through if no un- or fork connections are avoided (see clear 15 permissible potential or no impermissible current see patent specification 1186 913). For this purpose, test triggers have occurred. This has made this process successful used, which identifies the to the coupling matrix that the holding current belongs to the holding Coordinate switches occurring marches at all coupling field inputs and all couplings series resistors connected upstream for their correctness and permissibility watch. Monitoring results obtained in this way have to flow that on the occurrence of inadmissible exploited the occurrence of sigem potential or impermissible current in each case on Incorrect settings of these crossbar switches to connect point between coupling field input or prevent. However, it cannot be ruled out that · the switching network output and the associated series resistor Irrespective of this, malfunctions due to electrical faults are checked so that after the entire. > occur; those outside the area of the Tioordi- »5 th connecting path via at least one of the data switches occur, especially at the connection points between associated coupling connecting points Intermediate lines. In addition, at the field input and upstream Vorwiderstana, this is the case Procedure for access to the connections as between the associated switching matrix output and of all crossbar switches required for test purposes. Such errors can be avoided if 30 is performed, the in cooperation with the affect holding current flowing through holding windings due to a connection request in the coupling The connection path to be switched through in the field is divided into parts of the coupling relays and the occupancy relays to the response which initially brings each chen one after the other, which then solely through the holding current be switched through for themselves, and if held at one that the occupancy relay to such partial connection is checked in each case, 35 responding current pulse only added whether the partial route in question is due to an electrical one, after having previously corresponded with the help of an m error an impermissible potential or an inappropriately caused by a test pulse casual current occurs; the entire connection path of the current pulse is the through-connection of the connection on the other hand it is only switched through if it has been confirmed in advance and that test pulses are used no inadmissible potential or no inadmissible 40 which are so low in energy that they in turn siger current had occurred (see SEL messages, no relay belonging to the switching network for the An-1963, Volume 3, pp. 98, 131). This ensures that you can speak.

that connection paths on which an electrical The invention thus shows how the test itself

Errors could have a disruptive effect, must even be carried out and not as intended for this purpose must first be switched through. 45 technical measures can also be used for this purpose

The object of the invention is now to provide a method to indicate the information inserted in intermediate lines, how to make the test relay relay respond in an expedient manner, andw. can be carried out for a partial route. beforehand, advantageously in a corresponding manner, it is also possible to proceed necessary for this in order to be able to confirm the circuitry measures at the same time for connecting through the connection path. speak of occupancy relays, which are used in In all these cases, the for P ™ feweckerfor intermediate lines are inserted, and moreover access to switching network inputs, and Y - from a confirmation of the connection of the switching network outputs

Depending on the subdivision of the connection ^{path into 6} ° of a stream is detected.

Partial routes result in a more or less precise The features and characteristics given above

Limitation of the location of the error, possibly effects of the invention, are shown below

except for a part of the way, z. B. in the form of an intermediate of several Auslührungsbeispielen explain in more detail

management. tcrt. Reference is made to FIG. I to 4 reference

The invention thus relates to a method for use.

Detecting electrical faults in a multi-F i g. 1 schematically shows a four-stage coupling-stage coupling field, which consists of relay couplers from field with crossbar switches and two-way coupling relays with trigger windings and holding lines;

5. 6th

Fig. 2 shows the course of a response artery between z. B. with the help of the

between a coupling field input and a coupling end contacts ei 2 and ez2 as well as with the help of the

field output; * The marking contact w2 is energized. Will

F i g. 3 shows the associated holding wire and all three contacts mentioned are closed at the same time.

Holds belonging to another connection path, then all response windings become simultaneous

wire as well as a conductive contact between the energized, which is not intended here

Holding wires; is sighted. According to the method according to the invention

F i g. FIG. 4 shows the speech cores which the in FIG. 3 ren, however, are z. B. initially by closing

shown holding wires are assigned. of contacts ei2 and n \ 2 the pick-up windings

There are now application options IA2a and IA2b energized , whereby the ten for the test procedure to determine electrical one half of the entire connection path as Irish errors in the multi-stage switching network is switched through to the first partial path. Then, hand of the four-stage coupling shown in FIG. 1, the contact et 2 is reopened and the field is explained instead. This coupling matrix has the coupling contact ez2 closed, whereby the other half stages A, B, C and D. Each coupling stage has 15 of the connection path as a second partial path through several coordinate switches. B. is switched by the response windings coupling stage A of the crossbar switch KA 1 and I A 2c and \ A2d are energized . With coupling stage D the coordinate switch KD 1. With the help of the dashed marking contacts an already switched connection path m21 and m22 can be switched through. B. the switching matrix input 71 connected to the coupling path in a different way divided into partial paths panel output Zl. Due to a connection request, which has already been indicated, the connection of partial routes using the connection path is z. B. the switching matrix input 72 mentioned marker contacts also has to connect to the paths with the switching matrix output Z 2. The routing in the switching network has to be taken into account, and this latter connection path can be divided into sub-paths in different ways, to the extent that the respectively activated con-ways. In any case, the relevant partial route is clocked in a manner known per se, and it is expedient that the partial routes as a whole are to be clearly defined in each case.
form the entire connection path. It will now be shown how to check whether z. B. each partial route just form half of the entire one partial route of the connection connection route to be switched through. But it can also z. B. 30 way a potential occurs, which lead from one already the first partial path only over a coupling stage of the switched through other connection path over the coupling field from the coupling field input or from the head inadmissible conductive contact of two line cores pelfeldausgabe, and it can be delivered afterwards. In doing so, a series of partial paths is switched through by the test, which is potentially detected by a potential occurring regularly on the respective via a further coupling stage including the line cores of the previously connected partial path leading to other connection paths. If a total of only two partial routes are co-determined. The check takes place at the stopping points, if this is done in the shortest possible time over which the stopping coil is wound in the coupling field. If a switched-through partial path leads in each case to lungs of the coupling relays of relay couplers via a further additional coupling stage, then 40 other are connected. If the connection paths are already connected, the location of any connection paths that may be present can be particularly easily and precisely delimited via these holding wires. Holding current for the coupling relays, which has the consequence

It can also be useful that a partial path that also on these holding wires each have a specific

in each case across all coupling stages except for one coupling potential occurs. If an improper contact

stage leads, which is on the edge of the switching matrix. 45 nmg of two such holding wires is present, it works

Is there a risk that the potential in question at the other edge of the

Coupling matrix lying coupling stage from an error on a partial route and can there with the help

occurs, especially small, it can then also be detected under test equipment, whereby this elec-

Under certain circumstances, the connection of a copy error is detected via this. In Fi g. 3 is now

pelstufe leading partial path shown at least in many 50 an example, such as a circuit arrangement

Cases can be saved. It is useful if it is necessary to build to prevent the occurrence of such inadmissible

to detect a partial path in each case via a potential at the edge of the coupler on a partial path. In the

The coupling stage lying in the field leads, since the previous in F i g. 3 are shown in FIG

seen testing then only connecting means having h designated holding wires in all Koppelfeld-

are required that arrive at the edge of the switching network and 55 pre-resist all switching network outputs.

are to be provided, which is usually connected upstream for this purpose, via which the holding current is supplied

is technically particularly easily accessible. has flow. In FIG. 3, however, only the holding

2 shows an example of how the switching matrix input 71, the setting wire e of the connection path connecting between and the switching matrix output Zl and the switching matrix input 72 and the coupling 60 to which the switching matrix input 72 are shown and the switching network output Z2 is to be switched through, the connection path connecting the switching field output Z2 is genetically constructed. It is assumed that you will hear. Accordingly, the crossbar switches of the switching network are only represented by these two connecting relay couplers. It is shown because of this. The series resistors Rv 1 in a structure known per se (see German 65 belong to the connection path between the Kop patent specification 1048956, Fig. 6). The input 71 and the coupling output Zl. stcliadcr inserted response windings I A 2a, the series resistors Rv2 belong to the connection ] A2b, IA 2c and lA2d of coupling relays are communication path between the Koppclfcldcingang 72 and

7 8

the coupling network output Z 2. There is a potential drop in the holding wires / i, which goes from potential + to the holding windings of the coupling relays in each case to ground potential. At the contact point, of the inserts and their associated upstream relay by invalid conductive contact contacts s given. So are in the holding wire between is, therefore a different potential than the potential switching matrix input Ύ2 and the switching matrix output 5 tial + occurs. This normally occurring Po- 71 the holding windings II A2a, IIAlb, UA2d tcntial also determines the potential that is inserted. In addition, these holding wires have an effect on the test device Ph and occupancy relays are inserted, which signal the operating state that is no longer equal to the potential + of the associated intermediate lines, as in the case described above. Have that yourself. These are the occupancy relays BAB2, io now effective potential represents an impermissible BBC2 and BCD 2. So it is a potential, and it is therefore through the test a holding wire, the switching device Ph in a known manner of the electrical fault in the form of which is technically structured (see German patent - inadmissible conductive contact reported. It is written 1048 956, Fig. 10). In a very corresponding way, therefore, the entire connection path in this case are in the holding wires A, which are not switched through by the switching matrix 15, since this only happens when input Tl leads to switching matrix output Zl that does not have an impermissible potential.
Pickup windings Il Ala, HAib, II A Ic and If the conductive contact is not present II A Id of coupling relays and the associated Re-, then, as already explained, no impermissible relay contacts are inserted. Occupancy relays are also inserted potential at the connection point between the coupling point, which are designated with BABl, BBCl and BCDl 20 field input T2 and associated series resistor RV 2 . So that the exam is on. A further partial switched partial path is then subsequently detected in each case the potential that is carried out, for which purpose the other connection paths that are regularly opened again by a contact et 2 that was previously closed on the holding wires is opened and then the contact ez 2 is closed, emerging potential is also determined in the event of a fault, »5 As already explained, the second partial path is switched through to the occurrence of impermissible potential of the connection path to be switched through at the connection point between the switching network, which has the consequence that the input or switching network output and associated holding windings II A 2 c and II A 2 d upstream series resistor tested. For this purpose, a test device relay contacts are closed. To check for Pft with the help of a contact at each of the 30 occurrences of impermissible potential, the connection point is switched on that belongs to a test device Ph via the contact hz 21 now through a partial connection to the connection point between the switching matrix part . For the connection path between output Z 2 and the associated series resistor, the switching matrix input T 2 and the switching matrix output Rv 2 are switched on. If there is no electrical fault path Z 2, the contacts Af 22 and ftz21 are used for this. 35 is present, then also this time it flows over the Haltewick-! gang 7Ί and the switching matrix outputZl are here II A2c and \\ A2d no holding current. It j is intended for the contacts ht 12 and hz 11. This time, therefore, the ground potential has an effect on the The operation of the circuit arrangement according to the test device Ph via the relevant Vorwider-Fig. 3 is now based on an operating example 40, R ν2 was outstanding. But this is not the case when explained. Due to the first partial connection for an impermissible conductive contact (not shown here) between the switching matrix input Γ 2 and the connection with a holding wire of another connection already switched through-switching matrix output Z2, ϊη this path is the one from switching matrix input T 2 to the case would arise the testing device Ph have an unacceptable potential for intermediate conduction between the coupling stages B 45. The entire connection and C leading partial route through. For this purpose, the connection path is switched through if no impermissible potential has occurred in both parts of the convergence in the manner already described. bars et 2 and wi2 closed. The consequence of this is that other parts of the entire pel relay can also form the connection path for the holding windings Π A 2 a and 5 °, as explained in the case of the above HA 2 b upstream relay contacts Operational example was provided.
will. In order to check for the occurrence of inadmissible As already stated, the contact Ar 22 closed through-connection can also be checked in each case with a partial potential, whether because of sen. If there is no electrical fault, an impermissible current flows through the series resistor Rv 2 and the holding winding 55 occurs. This stream can e.g. B. also because of genII / 42a and HA2b no power. As a result of an impermissible conductive contact with a line, the test device Ph is under the influence of the line wire of the connection path to be switched through at the free end of the relevant series resistor with a line wire of an already through-connected Rv 2 potential +. If, on the other hand, the other connection paths flow. A conductive contact s shown in FIG. 3, which is checked in this way, can be constructed in exactly the same way as the one shown in FIG. 3, which incidentally also leads via relay windings. As series resistors can then be used, so a moderate rectifier acts on the testing device PA, which has a different potential than before. The fact is that the holding current in the passage is suspended via it, so that the connection path between the 65 direction flows. To check for current, the jc switching matrix input 71 and the switching matrix output are already switched through at the connection point between the Koppclfeld-Zl. Via the Halteadcr /; Therefore, if a rectifier occurs, the relevant mentioned equilibrium

209637/369

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Richter hears in the direction demanding electrical. In the same way as for the previous be test pulse. For this purpose, the in FIG. 3 test, the contacts ht 21 function also result in a current flow when an inadmissible contact is provided for the test of the partial contact with the holding wire of another connection path that has already been connected through the connection path 5 to be transmitted is. between the switch fabric input Tl and the LAD In this operation example, the entire Verbinpelfeldausgang Z 2 is used. These contacts only pass through if the contacts Ar 11 and hzl2 speak beforehand, for which no impermissible current had occurred. The connection path that has already been switched through can be subdivided into partial paths in different paths between the switching matrix input Tl and the io way, as were to be used in an switching matrix output Zl. the context of which has already been explained. As for the operating example angenom- also ohmic resistors is vermiemen into the retaining wires that first a partial path is switched, the are is at the same time avoiding that there one of the leads to the switching matrix input Tl and then a disturbing heat generation occurs. Partial path is switched through, which leads to the switching matrix 15 In the circuit arrangement according to FIG. 3 who output Z 2 leads and each half of the total uses the switching points, which includes the coupling connection path. Accordingly, field inputs and the switching network outputs are in the through-connection of the first partial route which the These nodes must be accessible, since holding windings UAIa and 11/4 25 h upstream in the holding with there impermissible for the presence Potenader relay contacts closed. 20 tials can be checked or so there electrical In addition, the Kon test pulses can be supplied to test for current. The Zugängtakt Λί21 temporarily closed, causing the Iichkeit these nodes can now vorteilam switching matrix input Tl connected direct way legally be also exploited to judge claimed to reverse. If the operation of a switching network to which the switched partial path is not from an electrical circuit arrangement according to FIG. 3 refers to seeing errors is concerned, so the test pulse did not ease. With such a switching matrix, the result is that a current flows. The switched-through relay coupler is composed, whose coupling partial path ends on the one hand at the rectifier mentioned in relay response windings and holding windings in the blocking direction, and in which in intermediate lines occupancy and has a free end on the other side. If relays have been inserted, namely after switching through the inadmissibly conductive pressure of the entire connection path, marked with s , there is also contact with the holding wire of the other connection path already switched through the occupancy circuit inserted in the holding wires, this results in response bring. There now flows a current path for the electrical test pulse, the holding wires, into which these occupancy relays are inserted via the holding winding UA la including the associated 35, a holding current which is dimensioned so that it reaches from the forward relay contact, the occupancy relay, to the coupling relay , to which the there- IiARl. the holding winding UAIa including the associated holding windings, continue to be held, upstream relay contact, the occupancy relay after they have already responded. In many cases BABl, the occupancy relay BBCl, the Haltewick- is this current not sufficient to trigger the insertion II Λ ic including the associated upstream Re- 40th occupancy relay, and relay contact, the occupancy relay BCD 1, the hold- if it is actually the If it were, it would be winding II A id including the associated upstream for these relays at least an unnecessarily high relay contact and the current at the switching network output Zt, since a loop-connected rectifier leads to ground to hold the relay. A lower current is sufficient than is sufficient for their response. The accessibility of the mentioned occurs is connected to a current that is determined by the switching points, the device Uh delivering the test pulse at the coupling field inputs and located at the coupling network outputs, whereupon the presence of the mentioned electrical system is advantageously exploited to avoid the situation Error is reported. The current can e.g. B. supply relays with a current pulse that makes them respond through the voltage occurring at a resistor. It will therefore be determined for this after a drop in voltage. If the check through the entire connection path over to current shows that a current actually occurs, at least one of the connection points between the entire connection path, the coupling field input that does not belong through, and the upstream one is switched. If, on the other hand, it has emerged that there is no current series resistor, which also occurs through a rectifier, the corresponding test can be formed for the 55, as well as carried out between the associated head-second partial path, this time the panel field output and the series resistor connected upstream, contact ftz22 there for the test on current which can also be formed by a rectifier, is closed and the device Vh this time a current pulse is supplied which, in cooperation, delivers an electrical test pulse which test current of the rectifier 60 connected upstream of the halo coupling field output Z2 that is already flowing with the holding windings Coupling relay has to claim the occupancy relay to the Anin Sjicrrichtung. When speaking first brings about the test described solely by the Haltcstuifii, a positive test pulse is to be held. For this purpose, those already mentioned can be used. When testing the second part, contacts ht 21 and hz 22 are used. On the other hand, a negative test pulse is to be used as a minimum, one of these contacts must be used accordingly. In this case, too, the occurrence of the entire connection path of a current can be temporarily closed by the occurrence of a voltage, and at this drop in a resistor it is to be determined at the point in time from the device Vh as large as the test pulse supplying device Vh ge current pulse / α supply that the desired effect

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is achieved in the occupancy relay. One of the contacts Iu 11 and was previously placed in a different way in connection paths that were already connected. The occurrence of impermissible potential hi \ 2 for the already connected connection is then used on the speech wires of the coupling path / 'between the coupling field input T1 and the field input or coupling field output of the Dutch coupling field output ZI. 5 connected connection path checked. For this

Advantageously, this and the test device Pa. To protect them appropriate other contacts yet for against excessive currents, the test potential Ua will exploit achieve further effects. This is because it is applied across one of the resistors Rp 1 or Rp2. It is advisable to also check the connection of a connection path because of a connection request, i.e. to check whether the connection partial paths of the connection path to be connected clocks of the coupling relays have actually taken their position between the coupling field input T 2 and the Kop working position. To this end, superiors pel field output Zl successively revised for himself that one can be switched on by a test pulse using, so here the following day before calling Before playing current pulse through the circuit transitions from. First of all, it is ensured that the connection path is confirmed. It is a 15 speech lines a, z. B. at the coupling network inputs such test pulse also with the help of one of the already through-connected connection paths, supplied to the mentioned contacts and applied by the test test potential Ua . Delivered at the switching matrix facility Uh. Appropriately, at input T1, the contact at 1 is used for this purpose in test pulses that are so low in energy, the operating position shown. Then when durchdaß they in turn no part of the switching matrix ao to be switched connection path z. B. which can bring the Kop relay to respond. The half leading to the panel field input T2 as part of the confirmation of the connection is only switched. In addition, the contact at 2 is brought into the operating position drawn from the delivery of a test pulse, through which a current flow is also connected. Because of the tests that took place before the test device Pa on the associated speech wire a , the partial switch-through »5 is switched on. When lines have already been switched through, it has already been ruled out that a connection path is all crosspoint contacts in such a current because of an electrical fault in the working position. When the connection is to be switched through, flows. The occupancy relay to respond brin- away only the crosspoint contacts ala and constricting current pulse is then alb'm after implementing working position. If there is no inadmissible conducting of the test for switching through the connection between two speech wires α, then the connection path is supplied. does the test potential Ua not affect the test

An example for a testing device Pa will now be given. However, this is the case when the

purifies, in which a potential is detected. In this case, impermissible conductive contact is indicated with an s

In this case, it is a potential that exists between two speech cores α. The bug will

by one only for test purposes in each case to the relevant 35 then reported with the help of the test device Pa , and

Fenden line cores of already through-connected it is prevented that the entire connection path

Connection paths temporarily created test is switched through. If necessary, it is now

potential is determined. For this, in particular, that half of the

other speech arteries in question, on which the connection path is connected as a partial path without special, Measures normally no potential occurs. It can 40 lead to the switching matrix output Z 2, whereby the coupling

but also other line cores in this way pelpunktkontaktea2c and ali in the working position.

checked if they are suitable for this. men. The test device Pa is now in place over

Are shown in Fig. 4 to the already treated at the contact az 2 via the contact 2 to the supplied communication paths belonging to a speech wires overall hearing opening vein α turned on. There is an electrical sign. They present fresh faults via the coupling contacts ala, al b, 45, so it is not under the input alc and aid and via the coupling point contacts the test potential Ua. The entire a2a, alb, alc and aid can then be used. When the coupling field inputs connection path are switched through, genes and coupling network outputs are also connected here can expediently be applied with a test device for holding. Combined with the intended test. Ir hear the contacts at 1, azl, at2 and az2. The test of the manner in question can auct potential Ua be tested on the speech wires α at the head all line field inputs belonging to the connection paths or at the coupling field outputs adem.

1 sheet of drawings

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Claims (10)

Patent claims: 1. A method for detecting electrical faults in a multi-stage coupling network, which is composed of relay couplers from coupling relays with pick-up windings and holding windings, in which in the intermediate line cores occupancy relays are inserted, which belongs to an indirectly controlled switching system, in particular a telephone exchange, in which one because a connection request in the switching network is divided into partial routes, which are initially connected one after the other in each case, in which in such a partial connection is checked whether an inadmissible potential or an inadmissible current occurs on the partial route in question due to an electrical fault, and in which the entire connection path, on the other hand, is only switched through if no inadmissible potential or no inadmissible current had previously occurred, characterized in that the holding current via the holding wires (h) at all heads field inputs (Tl ... Tl ...) and all coupling network outputs (Zl ... Z 2) upstream series resistors must flow, so that the occurrence of impermissible potential or impermissible current at the connection point between coupling network input (T 2) or Coupling matrix output (Z 2) and associated series resistor (RVl, RVl) is checked that after switching through the entire connection path (7 "2-Z 2) via at least one of the connection points between the associated coupling matrix input (Tl) and upstream series resistor (RvI) and between the associated Coupling network output (Z 2) and upstream series resistor (R ν 2), a current pulse is supplied which, in cooperation with the holding current of the coupling relays (BABl, BBCl, BCDl) already flowing via holding windings (UAIa, UlAIb, WAIc, UAId) , is used to respond brings, which are then held solely by the holding current, that the current pulse causing the occupancy relay to respond is only supplied after previously with H With the aid of a current pulse generated in a corresponding manner by a test pulse, the connection of the connection path was confirmed, and test pulses are used which are so low in energy that they cannot trigger any relay belonging to the switching network. 2. The method according to claim 1, characterized in that ohmic Vorwiderstäiide (/ ir I, RvI) are used and that a check is made for the occurrence of impermissible potential. 3. The method according to claim 1 or 2, characterized characterized in that it is checked whether a potential occurs that is already switched through Another connection path via the impermissible conductive contact between two conductors is delivered. 4. Atispii method: ·. ■■ ·> "* thereby rejects, that the test has a potential that is co-determined by a potential occurring regularly on the relevant line cores (h) from other connection paths (e.g. Γ 1-Zl) that have already been switched through. 5. The method according to claim 3, characterized in that the test detects a potential (z. B. Tl-Zl) through a only for test purposes each to the respective line wires (a) by already switched connection paths temporarily applied test potential (Ua ) is determined. 6. The method according to claim 5, characterized in that the test potential (Ua) is applied to the speech wires (α) at the switching network inputs (z. B. Tl) or at the switching network outputs (e.g. Zl) of already switched connection paths and that on the occurrence of impermissible potential on the speech wires (a) of the switching matrix input (T 2) or switching matrix output (Z 2) of the connection path to be switched through is checked. 7. The method according to claim 1, characterized in that rectifiers are used as series resistors (RvI, RvI) through which the holding current has to flow in the forward direction, and that to test for current at the connection point between switching network input (T 2) or switching network output (Z 2) and the associated rectifier, an electrical test pulse demanding the relevant mentioned rectifier in the reverse direction is supplied. 8. The method according to claim 7, characterized in that it is checked whether a current occurs because of an impermissible conductive contact with a line core of the Connection path with a line core of another connection path that has already been switched through can flow. 9. The method according to any one of the preceding claims, characterized in that test results can be used to isolate the location of the fault. 10. The method according to any one of the preceding claims, characterized in that in the in the manner in question, all line cores belonging to connection paths are checked.