GB2162003A

GB2162003A - Earth leakage circuit breakers

Info

Publication number: GB2162003A
Application number: GB08511496A
Authority: GB
Inventors: Stanley William Clives
Original assignee: Ashley Accessories Ltd
Current assignee: Ashley Accessories Ltd
Priority date: 1984-05-05
Filing date: 1985-05-07
Publication date: 1986-01-22
Also published as: GB8511496D0; GB2162003B

Abstract

A mains earth leakage circuit breaker (10) has associated means (12) sensitive to abnormal neutral line conditions. A sensing device (14) connected between the live and neutral lines AL,AN controls a switch (16) so that, in abnormal neutral conditions, the switch passes an electrical signal into the earth line (AE) that will be detected as a fault by the elcb (10). <IMAGE>

Description

SPECIFICATION Electrical neutral abnormality detection The invention relates to electrical mains driven circuits and has particular reference to detection and response to abnormal neutral line conditions.

We have been investigating mains circuit fault-tripping systems and have made several proposals, see patent applications Nos.

8404351, 8332814and and 8332815 including earth leakage circuit breakers and use of same for individual appliance circuits, such as at plug-and-socket connections therefor. Those proposals concern particular systems suitable for compact incorporation into electrical accessories, particularly socket outlets, and tripping out at detection of polarity reversal. We believe that there is a clear further need for detection of departures from normal neutral conditions, at least where danger can arise as in so-called loss of neutral, i.e. where an appliance becomes inoperative because of a circuit break in the neutral side, and so ceases to work but without necessarily tripping out an associated circuit breaker, and dangerously leaving the energised side live.

It is thus an object of this invention to satisfy such need, and to so in a manner that aids response by an earth leakage circuit breaker.

According to a specific aspect of this invention, there is provided apparatus affording a circuit path between live and neutral lines via means sensitive to abnormal neutral conditions and operative then to pass an electrical signal into an earth line.

In general, our proposal is for practical alternatives to monitoring the neutral line itself, say via an additional toroidal sensing core.

In that general sense, then, this invention comprehends controlling and controlled connections to live, neutral and earth lines, whether on the load side of an earth leakage circuit breaker device or on the supply side where an associated accessory has an on/off switch, with control means to detect neutral line abnormality and, in response thereto, inject an electrical signal into the earth line thereby creating what appears to be an earth leakage fault condition, i.e. detectable by such preferred earth leakage circuit breaker device.

Specific embodiments hereof may thus in clude a relay, which may be a suitable electronic circuit type, say utilising solid-state semi-conductor means. In relay terms, such means will afford a selective path for an electrical signal to go into the earth line, say as by closing a switch from live, or from electronic circuit breaker normal neutral return, to earth, that path being held closed or otherwise unenergised for as long as there is no neutral abnormality to be detected.

Specific implementation of this invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is an outline circuit drawing for one embodiment; and Figure 2 is a detailed circuit drawing for an embodiment with active electronic circuit breaker control.

In Fig. 1, a residual current operated device, specifically an earth leakage circuit breaker 10 is shown in maims supply lines ML, MN and ME (standing for live, neutral and earth). If desired, that circuit breaker 10 may be incorporated into a socket outlet. In any event, system feed lines AL, AN and AE are shown going from the circuit breaker 10 ultimately usually to an appliance, though detection hereof is concerned with any control circuitry or equipment after the star-point, i.e.

not just with appliance faults but generally with neutral abnormality.

Those lines AL, AN, AE have associated therewith loss of neutral detection-and-response means 1 2 that basically comprise any suitable electronic two-state switch that, characteristically, resides in its OFF state whenever normal voltage conditions apply between live AL and neutral AN lines, and changes to its ON state whenever such conditions cease to exist, the ON and OFF states relating to flow of electrical current from its live line AL to the earth line EL, such flow then being a signal often a short impulse, sufficient to be seen by the earth leakage circuit breaker 10 as the equivalent of an earth leakage fault to be detected.

This action is illustrated diagrammatically in dashed lines within the box 1 2 by, between lines AL and AN, hold means 14 for a switch 1 6 between lines AL and AE, and a current/voltage control device 1 8 in series within the switch 16.

As will be evident, the means 1 2 is required only to detect and respond to the abnormal neutral line condition as, once it has responded, the entire circuit feed can be interrupted by the circuit breaker 10, often in a double-pole switched manner. In practice, of course, as the danger concerned here relates to line AL being live, a single-pole action of the circuit breaker 10 would suffice.

In relation to incorporating provisions for detecting loss of neutral into the circuit breaker 10 of our copending application no.

8430852, we now turn to Fig. 2.

In Fig. 2, the integrated circuit 20 actively monitors the toriodal core 22 normally for earth leakage sensing at winding 22S as an imbalance between live and neutral lines 22L and 22N also transversing the core 22. Injection winding 101 on the core 22 serves in causing earth leakage simulating conditions at either test via button switch 24 or polarity reversal via resistor 26R and capacitor 26C, all as described in the aforementioned application relative to operation of circuit breaker switch 28 controlled by solenoid 28S.

For the purposes hereof, it will be appreciated that, if the neutral is lost, the integrated circuit 20 will have no effective return, shown from its pin 4 via the lower left diode of bridge 30 to circuit node 32, and will thus be unable to respond at all. To counter that, switch 34 is shown controlled by an abnormal neutral sensing relay 36 to go to change state from that shown to a circuit path 38 to earth at 40, actually via a further winding 22F of the core 22.

The relay 36 is shown connected between live and neutral lines at the supply side of a local switch 42, typically of an accessory associated with the circuit breaker. When the relay 36 triggers, the switch 34 will change over and the winding 22F will unbalance the core 22 sufficiently to trigger the integrated circuit 20, via the sense winding 22S.

Claims

1. A mains earth leakage circuit breaker further comprising first means for sensing abnormal neutral line conditions and second means responsive to the first means for passing an electrical signal into an earth line sufficient to be detected as an earth leakage fault.

2. A mains earth leakage circuit breaker according to claim 1, wherein the first means is connected between live and neutral lines or terminals therefor.

3. A mains earth leakage circuit breaker according to claim 2, wherein the first means comprises a relay and the second means comprises a switch controlled by the relay.

4. A mains earth leakage circuit breaker according to any preceding claim, wherein the second means selectively makes and breaks a circuit path from the live line or terminal therefor.

5. A mains earth leakage circuit breaker according to claim 4, wherein the first and second means are connected on the load side of earth leakage tripping control circuitry.

6. A mains earth leakage circuit breaker according to any one of claims 1 to 3, wherein the second means selectively makes and breaks a circuit path for low voltage return from active electronic control means for earth leakage operating purposes.

7. A mains earth leakage circuit breaker according to claim 5, wherein said circuit path is via a winding on a toroidal core also having a sensing winding connected to said electronic control means.

8. A mains earth leakage circuit breaker according to claim 6 or claim 7, wherein the first means is on the supply side of an on/off switch itself on the supply side of the circuit breaker.

9. A mains earth leakage circuit breaker arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawing.