GB2381968A

GB2381968A - Earth leakage currrent circuit breaker

Info

Publication number: GB2381968A
Application number: GB0222305A
Authority: GB
Inventors: Dante Bagalini; David Alexander Elrick
Original assignee: Circuit Breakers Ind Ltd
Current assignee: Circuit Breakers Ind Ltd
Priority date: 2001-10-22
Filing date: 2002-09-25
Publication date: 2003-05-14
Anticipated expiration: 2022-09-25
Also published as: CN1233011C; CN1414589A; GB0222305D0; GB2381968B

Abstract

An earth leakage circuit breaker is arranged internally so that it is unusually compact, and is of the same external dimensions as a non-earth leakage circuit breaker in a range of such circuit breakers. This is achieved by locating a toroidal magnetic sensing core 126 between line terminals 136.1, 136.2 of the circuit breaker and its contacts 120, with live and neutral conductors 132, 134 extending transversely from the line terminals 136.1, 136.2, through the core 126 and back to auxiliary line terminals 150 located adjacent the external line terminals and separated from the external terminals by an insulating wall or partition 152.

Description

CIRCUIT BREAKER THIS invention relates to an earth leakage circuit breaker.

Circuit breakers incorporating an earth leakage detection circuit are widely used and generally detect earth leakage by monitoring the current in live and neutral conductors supplying a load. If there is a discrepancy in the current in the live and neutral conductors above a predetermined threshold, a sensing circuit operates the circuit breaker mechanism, disconnecting the load from the supply.

A conventional earth leakage circuit breaker of this kind employs a toroidal magnetic core as a sensing element. The live and neutral conductors between the circuit breaker contacts and the load terminals of the circuit breaker pass through the core, and a winding on the core senses any magnetic field due to a current imbalance in the two conductors, providing a signal to the sensing circuit. Although earth leakage circuit breakers have become more and more compact in recent years, they are generally bulkier (wider and longer) than standard circuit breakers, due to the need to accommodate the toroidal core and the necessary sensing circuit. This has several negative consequences.

On the production line, the fact that the circuit breaker trip mechanism is different from the mechanism used In an otherwise similar standard circuit

breaker causes increased complication and lowers productivity. In actual use, typically in a switchboard or distribution board, the spacing between rows of circuit breakers is dictated by the spacing required by the largest items. The fact that the earth leakage unit is usually longer than a standard circuit breaker means that space is wasted between rows of circuit breakers.

It would be desirable to provide an earth leakage circuit breaker which can be housed in a standard circuit breaker housing.

According to the invention there is provided an earth leakage circuit breaker comprising a housing, a circuit breaker mechanism having live and neutral line terminals and live and neutral load terminals, and an earth leakage sensing circuit comprising a magnetic sensing core disposed about live and neutral conductors extending between the live and neutral line terminals and the circuit breaker mechanism.

The magnetic sensing core may be a toroidal core through which the live and neutral conductors pass.

Preferably, the conductors extend between the live and neutral line terminals and respective auxiliary terminals adjacent the live and neutral line terminals, the circuit breaker mechanism being connected to the respective auxiliary terminals.

The housing is preferably of the same external dimensions as the housings of otherwise similar non-earth leakage circuit breakers in a range of such circuit breakers.

The invention is described further hereinafter by way of example only, with reference to the accompanying drawings in which: Figs. 1 to 3 show front, side and schematic views, respectively, of a conventional earth leakage circuit breaker; Fig. 4 shows the mechanism of a conventional earth leakage circuit breaker, and in particular the disposition of a toroidal sensing core between the load terminals and the circuit breaker contacts; Figs. 5,6 & 7 illustrate front, side and schematic views of an earth leakage circuit breaker embodying the invention, corresponding to the views of Figs. 1,2 and 3; Figs. 8 illustrates the live side of an earth leakage circuit breaker embodying the invention; and Fig. 9 is a partial view of the circuit breaker of Fig. 8 with its casing and neutral pole omitted for clarity, illustrating the arrangement of the toroidal sensing core thereof.

Figures 1 and 2 show the general arrangement of a conventional earth leakage circuit breaker (ELCB) which is designed for use in conjunction with a range of conventional miniature circuit breakers. The electrical arrangement of the circuit breaker is illustrated schematically in Figure 3.

The ELCB of Figures 1 to 3 comprises a moulded plastics housing 10 which carries pairs of line and load terminals on its upper and lower ends,

respectively. On a front panel 12, respective switch handles 14 and 16 and a test button 18 are located.

As indicated in Figure 3, the circuit breaker has a pair of contacts 20 which are controlled by a tripping mechanism 22. Also located within the housing are a printed circuit board 24 which carries the earth leakage sensing circuit, and a toroidal magnetic sensing core 26 which is arranged so that live and neutral conductors 28 and 30 which extend between the contacts 20 and the live and neutral load terminals (34. 1, 34.2 and 36. 1, 36.2 respectively) pass through it.

Figure 4 shows the actual physical layout of the conventional ELCB of Figures 1 to 3, from which it can be seen that the toroidal core 26 is housed in a compartment 32 defined in a lower portion of the housing 10, between the contacts 20 and the load terminals 36. Note that in Figure 4, only the live side of the circuit breaker is shown, with the neutral pole and its respective conductors and terminals omitted for clarity.

It will be appreciated that, compared with a conventional standard miniature circuit breaker mechanism, the conductors 28 and 30 on the load side of the circuit breaker are longer and are routed differently. This requires a production line facility to be adapted specially to produce such ELCB's.

Referring now to Figures 5 and 6, an earth leakage circuit breaker according to the invention is shown. It will immediately be apparent that the housing 110 of the ELCB of the invention is much more compact than that of the conventional ELCB described above, the relative size of which is illustrated by the dotted lines in Figures 5 and 6. The housing 110 has the same width and height as the housings of conventional miniature circuit breakers In a range of known circuit breakers.

This is achieved not merely by miniaturisation of components, but by rearranging the components of the ELCB. In particular, the toroidal magnetic sensing core 126 is located on the line side of the circuit breaker

mechanism, between respective live and neutral line terminals (136. 1, 136.2) and the circuit breaker contacts 120, as indicated schematically in Figure 7. Thus, the live and neutral conductors 128 and 130 on the load side of the contacts 120 can be connected to the load terminals (154. 1, 154.2) conventionally, as in a non-earth leakage circuit breaker forming part of the same range of circuit breakers, while respective live and neutral conductors 132 and 134, extending between the respective live and neutral line terminals and the contacts 120, pass through the toroidal core 126 on the line side of the contacts.

Although the amount of space within the circuit breaker housing for accommodating the toroidal core 126 on the line side of the contacts 120, near the line terminals (136. 1 and 136.2) of the ELCB, is very limited, the present invention achieves this by splitting the line side terminals into two parts, a generally conventional external terminal and an auxiliary internal terminal. This arrangement is best shown in the pictorial views of Figures 8 and 9, which show the internal mechanism of a circuit breaker of the invention, with one pole (the neutral pole) of the mechanism omitted for clarity.

A line terminal 136 which is conventional in its configuration is formed from brass plate and has a contact tab 138 which is spot welded to a first, line side end 140 of a copper conductor 142. The conductor 142 extends transversely away from the terminal 136 into a small cavity 144 defined within the upper rear portion of the housing 110, in which is housed the toroidal core 126 with its axis upright. The conductor 142 is bent tortuously as shown, to define an intermediate portion 146 which passes axially through the toroid, and is then bent again so that it extends parallel to the line side end portion 140, and then kinked at a load side end portion 148 thereof so that it can be spot welded to an auxiliary internal terminal or contact 150. The auxiliary terminal 150 is separated from the terminal 136 by an insulating internal wall or partition 152 defined by the circuit breaker housing, which is moulded from a plastics material.

The auxiliary terminal 150 extends inwardly into the circuit breaker housing to define one side of one of the contacts 120, similarly to conventional practice, and the remainder of the circuit breaker mechanism is substantially conventional, with the load terminal 154 being connected via a short copper link 156 to the tripping coil 158 of the circuit breaker mechanism in a conventional manner.

The neutral side of the circuit breaker is laid out similarly to the live side described above.

The use of split line terminals and the specially shaped and formed line side conductors 142 allows the accommodation of the sensing toroid on the "line side"of the circuit breaker, enabling a surprising degree of compactness to be achieved, and making it possible to provide a fully specified earth leakage circuit breaker which is no larger in width and height than conventional miniature circuit breakers of an existing range.

This has obvious advantages both in use, where electrical switchboards and distribution boards can be fitted with such ELCB's without wasted space, and in production, In reducing the extent to which a production line for conventional circuit breakers must be adapted to produce ELCBs.

Claims

1. An earth leakage circuit breaker comprising a housing, a circuit breaker mechanism having live and neutral line terminals, live and neutral load terminals, and a set of contacts between the line and load terminals, and an earth leakage sensing circuit comprising a magnetic sensing core disposed about live and neutral conductors extending between the live and neutral line terminals and the set of contacts.

2. An earth leakage circuit breaker according to claim 1 wherein the magnetic sensing core is a toroidal core through which the live and neutral conductors pass.

3. An earth leakage circuit breaker according to claim 1 or claim 2 wherein the live and neutral conductors extend between the live and neutral line terminals and respective auxiliary terminals adjacent the live and neutral line terminals, the set of contacts being connected to the respective auxiliary terminals.

4. An earth leakage circuit breaker according to claim 3 wherein each of the live and neutral conductors has a portion which extends transversely between the respective line terminal and the magnetic sensing core, a portion which extends through the core, and a portion which extends between the core and the respective auxiliary terminal.

5. An earth leakage circuit breaker according to claim 3 or claim 4 wherein the respective line terminals and auxiliary terminals are located adjacent one another.

6. An earth leakage circuit breaker according to claim 5 wherein each respective line terminal is separated from the respective auxiliary terminal by an insulating wall or partition defined by the housing.

7. An earth leakage circuit breaker according to any one of claims 1 to 6 wherein the housing is of substantially the same external dimensions as the housings of otherwise similar non-earth leakage circuit breakers in a range of such circuit breakers.

8. An earth leakage circuit breaker substantially as herein described and illustrated with reference to Figures 5 to 9 of the drawings.