GB2135542A

GB2135542A - Earth leakage circuit breaker

Info

Publication number: GB2135542A
Application number: GB08404351A
Authority: GB
Inventors: Stanley William Clives
Original assignee: Ashley Accessories Ltd
Current assignee: Ashley Accessories Ltd
Priority date: 1983-02-19
Filing date: 1984-02-20
Publication date: 1984-08-30
Also published as: GB8404351D0; GB2135542B

Abstract

An earth leakage circuit breaker comprises means 30 for sensing leakage current flow to earth, means 20, 22 responsive thereto automatically to open at least one contact that interrupts current supply and means 46, 48 serving in the circumstance of reversal of live and neutral connections to produce the effect of earth leakage current flow at a detectable level for the sensing means 30. <IMAGE>

Description

SPECIFICATION Earth Leakage Circuit Breaker The invention relates to so-called earth leakage circuit breakers.

Earth leakage circuit breakers have usually been connected at incoming mains supply positions for particular sub-circuitry, often within panelboard, or otherwise by professional engineers/electricians or technicians under their control.

It is, however, the case that earth leakage circuit breakers are finding increasing use on separate circuits away from the panelboard or consumers unit and in situations where installation is less closely controlled, even done by laymen, with consequent risks from reversal of "live" and "neutral" connections.

All earth leakage circuit breakers require means for sensing leakage current flow to earth and means responsive thereto automatically to open at least one contact that interrupts current supply.

According to this invention, an earth leakage circuit breaker is further provided with means serving in the circumstance of reversal of live and neutral connections to produce the effect of earth leakage current flow at a detectable level for the sensing means, preferably and conveniently as an actual earth current flow that is artificial in the sense of being independent of any such flow to be detected normally.

One particular known type of earth leakage circuit breaker has a contact or contacts, often one for each of live and neutral lines, for making or breaking current flow; means for operating same, often a mechanism such as a relay operable either manually or by electrical signals thereto; and means for sensing an out-of-balance condition between live and neutral lines and generating electrical signals to cause the contact operating means to break the contact(s). A toroidal core transformer is suitable as the lastmentioned means with windings from line and neutral of a particular electrical circuit which windings produce cancelling magnetic flux in the core for no earth leakage in that circuit, and a signal winding for producing an electrical signal when the first-mentioned windings produce incompletely cancelling flux in the core.

For such an earth leakage circuit breaker, the further means hereof can conveniently comprise a limited-current-flow connection to earth from the neutral line of the circuit controlled by the circuit breaker, say via a series connection of a resistor of suitable ohmic value and a blocking diode poled for current flow to earth. The resistor value and the diode are chosen in relation to the known effective leakage current required to operate the circuit breaker, the 12T energy that can be safely dissipated by the resistor and diode, and assuring that the vectorial resultant of current flow in circuit conditions will not affect the sensitivity of the circuit breaker.

Such provision is cheap to implement, effective in operation, and will not usually require any significant change to the overall housing/case of a circuit breaker.

One embodiment of the invention will now be specifically described, by way of example, with reference to the accompanying drawing showing an electrical circuit diagram.

In the drawing, a single-phase, two-pole earth leakage circuit breaker 10 has a suitable case or housing indicated by chain-dashed box 12, and has live, neutral and earth input terminals 14L, 1 4N and 14E, and similar output terminals 16L, 1 6N and 16E. The input terminals 1 4L and 1 4N are both shown with make/break contacts 18L, 1 8N that are mechanically ganged (20) for simultaneous operation by a trip coil 22, usually also manually by a suitable push-button (not shown).From contacts 18L, 18N, the live and neutral sides are taken at 24, 26 to windings 28L, 28N, respectively, on a toroidal core balancesensing transformer 30, and thence at 32, 34 to the output terminals 16L, 16N. The transformer 30 also has a signal winding 36 connected to the trip coil 22 and serving to energise the latter so as to achieve the desired make and break of contacts 18L, 18N for below and above threshold for earth leakage.

A conventional test connection is shown via resistor 38 and test button switch 40 from the line 32 to the line 26. Also, output terminals 1 6 are shown connected to a load or loads 42, such as an electrical appliance or a socket therefor.

Thus far, the earth leakage circuit breaker 10 of known conventional type. Implementation of this invention is by the further provision of a reverse phase detection connection at 42 from the line 34 to line 44 between input and output earth terminals. That connection includes a resistor 46 of suitable ohmic value in series with a blocking diode 48 poled for current flow from line 34 to line 44.

As mentioned above, the resistor 46 is chosen to be within limits set the actual fault current required to break the contacts 1 8 via the trip coil 22 and signal winding 36 and the 12T energy that can be dissipated safely by the body of the resistor 46 and its associated blocking diode 48, and the combination of the register 46 and blocking diode 48 is such that the vectorial result of current passed in correct conditions will not affect the serviceability of the circuit breaker in sensing desired earth leakage, but that, in reverse phase connection condition, there will be swift and effective tripping to break the contacts 1 8.

it will be appreciated that the illustrated circuit breaker cannot be kept closed if the live and neutral are incorrectly connected in reverse polarity, thus ensuring safety from the results of incorrect connections and/or undetected earth leakage. Moreover, should the diode break down, the circuit breaker will automatically trip out without burning out the resistor and will, as before, not allow operation of the controlled circuit until corrective action is taken.

Claims

1. An earth leakage circuit breaker comprising means for sensing leakage current flow to earth, means responsive thereto automatically to open at least one contact that interrupts current supply and means serving in the circumstance of reversal of live and neutral connections to produce the effect of earth leakage current flow at a detectable level for the sensing means.

2. An earth leakage circuit breaker as claimed in claim 1 wherein the earth leakage current flow is artificial in the sense of being independent of any such flow to be detected normally.

3. An earth leakage circuit breaker as claimed in claim 1 or 2 wherein the last mentioned means comprises a limited-current-flow connection to earth from the neutral line of the circuit controlled by the circuit breaker.

4. An earth leakage circuit breaker as claimed in claim 3 wherein said connection is a series of connections of a resistor of suitable ohmic value and a blocking diode poled for current flow to earth.

5. An earth leakage circuit breaker substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.