GB2048580A

GB2048580A - Testing terminal unit and plug

Info

Publication number: GB2048580A
Application number: GB8008081A
Authority: GB
Original assignee: CA Weidmueller GmbH and Co
Current assignee: Weidmueller Interface GmbH and Co KG
Priority date: 1979-04-17
Filing date: 1980-03-10
Publication date: 1980-12-10
Also published as: CH649418A5; GB2048580B; IT1136122B; FR2454713B1; IT8012439A0; DE7911166U1; IT8015124V0; FR2454713A1

Abstract

An electrical terminal unit, primarily intended for connecting an ammeter to a current transformer secondary winding, has respective terminal members 3 normally interconnected by a resilient bridging contact 5, and testing contacts 4' for connecting the terminal members to test apparatus by means of a test plug 12. The testing contacts 4' extend beyond the bridging contact by an amount greater than that by which the plug contacts 10 are set back from the forward end 9 of the plug. The forward end of the plug serves to disconnect the bridging contact when the plug is inserted, after the plug contacts have made contact with the testing contacts, so that the transformer secondary circuit connected to the terminal unit remains closed. <IMAGE>

Description

SPECIFICATION Testing terminal unit and plug This invention relates to an electrical terminal unit designed two receive a plug for connecting a testing or monitoring circuit to a device connected to the terminal unit, orto enable work to be carried out on part of the connected circuitry without interference with another part of the connected circuitry.

In the case of an ammeter driven by a current transformer, it is essential to prevent the secondary circuit from being open at any time, because opening of the circuit would lead to danagerous voltages.

However, it is sometimes necessary to connect a testing instrument into the secondary circuit, or to remove or exchange the ammeter. Such operations must be carried out without breaking the secondary circuit. Similar problems can arise in other installations where it is necessary to change circuitry without breaking a particular circuit or part of a circuit.

German Patent Specification No. 601908 discloses aterminal unit for connecting an ammeter to a transformer secondary winding, the terminal unit being designed to permit a testing instrument to be connected into the secondary circuit without the latter becoming open. The terminal unit includes a slidable series link normally fastened in the closed position by screws and covered by a protective lever.

The test instrument is connected to a special plug which is inserted into the terminal unit in parallel with the link and which on insertion pivots the lever away from the screws so that, after the plug has been inserted, the link can be unfastened and slid to an "open" position, so that the secondary circuit is completed through the plug and test instrument. In its open position, the link prevents removal of the plug, so that the plug cannot be removed until the link has been returned to its "closed" position.

However, the construction and operation of this system is complicated, and it does not completely eliminate human error, since it would be possible for the user to forget to slide the link and to screw it fast.

It is therefore an object of the present invention to provide a terminal arrangement in which faulty connections are prevented automatically and which nevertheless is of simple construction.

In one aspect, the present invention provides, in combination: an electrical terminal unit having two separate terminals and a bridging contact which normally resilient interconnects the said terminals, each terminal having in the vicinity of the bridging contact a respective testing contact; and a plug having an insulating casing adapted to be inserted into the terminal unit and contacts in the casing for engagement with the testing contacts of the terminal unit, the plug having an insulating portion arranged to disengage the bridging contact from the said terminals after engagement of the testing contacts with the contacts of the plug, on insertion of the plug into the terminal unit.

In another aspect, the invention provides, a testing terminal unit with a least two metal parts, constructed as terminals, which can be connected to each other by means of a break plug, and with means for preventing faulty contacting, characterised in that the unit is provided with a clip-shaped contact spring which resiliently contacts the terminals, and connecting pins of the terminals extend beyond the contact springs by a distance which is greater than the distance by which an insulating material nose of a break plug, adapted for insertion into the testing terminal and containing the test apparatus connections and adapted for spreading apart the contact spring, projects beyond the contacts of the plug.

Normally. the terminals ofthe terminal unit are interconnected by the bridging contact or contact spring. In the case mentioned earlier, this will be the secondary circuit of a current transformer. The design of the terminal unit and plug are such that, when the plug is inserted, its contacts interconnect the terminals of the terminal unit, before the plug disconnects-the bridging contact.

The contacts of the plug may for example be connected to a testing instrument, which is thereby connected in series with the transformer secondary winding and the ammeter normally connected to this, or a by-pass link to close the transformer secondary circuit while the ammeter is discon- nected.

When the plug is removed, the bridging contact is allowed to close, before the plug contacts become disconnected. Consequently, it is automatically ensured that the circuit through the terminal unit is never open, automatically and without any intervention on the part of the user, whenever the plug is used.

An embodiment of the invention is shown, by way of example, in the accompanying drawings, in which: Figure 1 is a simplified side view of a testing terminal unit and associated plug, and Figures 2 to 4 are cross-sectional views of the terminal unit and plug, at three different stages of insertion of the plug.

The terminal unit shown has a flat rectangular slab-like-insulating casing 1 which can be clipped onto and unclipped from a support rail 11 of standardised dimensions means of a retaining clip, on the base of the casing. Inside the casing are two flat metal members 3 each with a plurality of upstanding flat connector pins 4, 4'. The pins 4 at the outer ends of the metal members 3 are terminal pins for connection of conductors by means of flat female connectors.

The inner pins 4' are for use as testing contacts, for connection of a test instrument into the circuitry connected to the terminal members 3.

The members 3 are normally interconnected, at their neighbourning ends, by a bridging contact 5 which, as shown in Figures 2 to 4, is a substantially U-shaped spring clip which embraces the lower parts ofthe members 3 and has contact dimples 6 on both sides, to ensure good and reliable contact with the members 3. The spring contact 5 is open at the top, and the upper ends of the limbs of the U have small outwardly flared portions 7.

A plug 12 is designed to fit into a socket in the top of the terminal unit and to ensure the testing contacts 4'. The plug has an insulating casing 8 containing contacts 10 connected to conductors 13.

Attheforward end of the plug casing is a projecting nose 9 of insulating material. The conductors 13 are connected to a test instrument or by-pass link.

The distance between the tips of the testing contacts 4' and the upper edge of the bridging contact 5 is greater than the distance between the tip of the insulating nose 9 and the contacts 10 of the plug. Consequently, when the plug is inserted in the terminal unit, as shown in Figures 2 to 4, the following sequence inevitably take place. Initially, the bridging contact 5 remains in contact with the terminal members 3, so that the circuit connected to the terminal unit, in particular a current transformer secondary circuit ammeter, remains closed. The contacts 4' enter the plug casing. As the plug moves further into the terminal unit, the contacts 4' make contact with the plug contacts 10; but the bridging contact 5 remains in contact with the contacts 4', as shown in Figure 3. Subsequently, with the contacts 4', 10 engaged, the nose 9 of the plug enters between the flared parts 7 of the bridging contact and forces the limbs of the latter apart, as shown in Figure 4, thereby disconnecting the bridging contact from the members 3, so that the latter are now interconnected only by way of the plug contacts 10 and the circuit connected to these.

When the plug is withdrawn, the reverse sequence takes place, with the bridging contact 5 closing onto the terminals members 3, before the plug contacts 10. become separated from the testing contacts 4'.

Consequently, the circuit connected to the terminal members 3 remains closed at all times.

Claims

1. In combination: an electrical terminal unit having two separate terminals and a bridging contact which normall resiliently interconnects the said terminals, each terminal having in the vicinity of the bridging contact a respective testing contact; and a plug having an insulating casing adapted to be inserted into the terminal unit and contacts in the casing for engagement with the testing contacts of the terminal unit, the plug having an insulating portion arranged to disengage the bridging contact from the said terminals after engagement of the testing contacts with the contacts of the plug, on insertion of the plug into the terminal unit.

2. The combination claimed in claim 1 in which the said portion is an insulating nose which projects forward of the contacts in the plug by a first distance, and the testing contacts project beyond the bridging contact by a distance greater than the first distance.

3. The combination claimed in claim 1 or 2 in which the testing contacts are coplanarflat metal members and the bridging contact is a general U-section sheet metal member with the limbs of the U on opposdite sides of the said metal members.

4. A testing terminal unit with at least two metal parts, constructed as terminals, which can be connected to each other by means of a break plug, and with means for peventing faulty contacting, characterised in that the unit is provided with a clipshaped contact spring which resiliently contacts the terminals, and connecting pins of the terminals extend beyond the contact spring by a distance which is greater than the distance by which an insulating material nose of a break plug, adapted for insertion into the testing terminal and containing the test apparatus connections and adapted for spreading apart the contact spring, projects beyond the contacts of the plug.

5. A terminal unit according to claim 4, characteirsed in that both sides of the contact spring are provided with contact bulges.

6. A terminal unit according to claim 4 or 5, characterised in that the top end of the contact spring is provided with flared portions.

7. Aterminal unit substantially as herein described with reference to the accompanying drawings.