GB2477954A

GB2477954A - Explosive gas detection unit and electrical fitting including such a unit

Info

Publication number: GB2477954A
Application number: GB1002853A
Authority: GB
Inventors: James Ian Henderson
Original assignee: Haven Ltd
Current assignee: Haven Ltd
Priority date: 2010-02-19
Filing date: 2010-02-19
Publication date: 2011-08-24
Also published as: GB201002853D0

Abstract

A gas detection unit 10 is provided comprising: a detector 16 for detecting the presence of an explosive gas in the atmosphere; a live input terminal 12L for connection to a live line of the mains electricity supply protected by a residual-current or earth-leakage circuit-breaker; an earth input terminal 12E for connection to an earth line of the mains supply; and a controllable switch 22 responsive to the detection of the presence of the explosive gas to complete a circuit between the live and earth connectors. Accordingly, when gas is detected, the unit 10 trips the circuit breaker, so that anything, for example, a light switch, fed from the same circuit breaker cannot cause an electrical spark which might ignite the explosive gas. The detector 16 may alternatively comprise a CO, CO2, relative humidity or temperature detector. The detection unit may be incorporated within an electrical fitting functioning as a power outlet socket, a light switch, or a standard mains power plug.

Description

TITLE

Ambience detection units and electrical fittings including such units

DESCRIPTION

This invention relates to ambience detection units and to electrical fittings including such units.

This invention was conceived as an explosive gas detection unit, but it is also applicable to detection of other characteristics of the environment or surroundings.

Many houses are supplied with gas, for example from a gas main or a gas bottle or tank. Most houses are also supplied with mains electricity.

Gas leaks can be caused by faulty gas pipework or gas fittings, or by a gas appliance being turned on without the gas being lit. If the concentration of gas reaches a particular level, a spark or flame can ignite the gas and cause an explosion with disastrous consequences, i.e. death and/or extreme property damage. The igniting spark or flame may be produced by, for example a match or cigarette lighter, but commonly is caused by a mains electrical switch being operated and sparking at its contacts, particularly when being turned off. Also, although the gases typically employed (methane, butane and propane) are not toxic, if the proportion of such gas in the atmosphere in a house becomes too high, it can result in asphyxiation and death even if the gas does not explode.

An aim of the present invention, or at least of specific embodiments of it, in connection with explosive gas leaks is to negate or reduce the risk of gas explosions caused by a gas leak followed by electrical sparking.

In accordance with a first aspect of the present invention, there is provided a gas detection unit, comprising: a gas detector for detecting the presence of an explosive gas in the atmosphere; a live input terminal for connecting the unit to a live line of a mains electricity supply protected by a residual-current or earth-leakage circuit-breaker; an earth input terminal for connecting the unit to an earth line of the mains supply; and a controllable switch responsive to the detection of the presence of the explosive gas to complete a circuit between the live and earth connectors.

In accordance with a second aspect of the present invention, there is provided a building having: a mains electrical system including a residual-current or earth-leakage circuit-breaker and mains distribution cables extending from the circuit-breaker; and at least one detection unit according to the first aspect of the invention connected to such a mains distribution cable.

The mains electrical systems of most houses nowadays have a residual-current or earth-leakage circuit-breaker at the distribution box. By connecting the gas detection unit of the invention to any location on a circuit fed by such a circuit breaker, detection of gas will result in the circuit breaker tripping at the distribution box so that subsequent operation of a switch (such as a light switch) fed by that circuit breaker will not result in a spark being produced. The gas detection unit is preferably designed to cause such tripping before the gas concentration is sufficiently high that any spark caused by the circuit breaker or by the controllable switch would ignite the gas. Also, the controllable switch is preferable of a type that does not produce sparks (e.g. a transistor, thyristor or triac), or in the case of, for example, a relay has sealed contacts.

There are other occasions when it may be desirable to trip an electricity supply and it would be convenient to do so without adding a significant amount of cabling to the electrical system. For example, in the event that the humidity in a room approaches saturation indicating that the room may be flooding, it would be desirable to trip the electricity supply to the room to prevent electric shocks. In the event that the carbon monoxide (CO) concentration in a room containing a boiler rises appreciably indicating that the boiler is not venting properly, it would be desirable to trip the electricity supply to the room so that the boiler turns off. In the event that the temperature in a room rises excessively indicating that there may be a house fire, it would be desirable to trip the electricity supply so that the electricity cannot cause further damage.

To deal with these eventualities, the gas detector of the first aspect of the invention may be replaced with any other detector for detecting a predetermined feature of the ambience of the detector, such as a CO detector, a carbon dioxide (C02) detector, a relative humidity detector, a temperature detector or an infra-red radiation detector.

The completed circuit is arranged to pass a current sufficient to trip the circuit breaker.

Typically the current may be at least 3OmA between the live and earth terminals when the live terminal is at the nominal mains voltage relative to the earth terminal. The current may be as great as at least 1 A. The controllable switch is preferably arranged to complete the circuit through a resistor.

The detection unit preferably further includes a neutral input terminal for connecting the unit to a neutral line of the mains supply. In the case where the detector is electrically powered, the unit may further include a power supply circuit for taking power from between the live and neutral input terminals and supplying power to the detector. Alternatively, in the case where a neutral supply is not available, for example in the case of a simple light switch having a live input, a switched-live output and an earth connection, the detector may be battery powered.

The detection unit may be incorporated into an electrical fitting. In one embodiment, the fitting may include live, neutral and earth output terminals connected to, or switchably connected to, the live, neutral and live input terminals for connection to a mains plug. The fitting can therefore also function as a power outlet socket. The fitting may include a plate for mounting on a mounting box so that the gas detector, input terminals and controllable switch are disposed inside the mounting box, with the plate being permeable to the ambience. The fitting may therefore be mounted, for example, to a wall mounted pattress box. The fitting may include a switched-live output terminal, and a manually-operable switch for connecting the live input terminal to the switched live output terminal. The fitting may therefore also function as a light switch. The fitting may include a housing containing the detector and the controllable switch, with the housing being permeable to the ambience, and the input terminals being provided externally of the housing. For example, the input terminals may be mounted on and project from the housing for insertion into a mains outlet socket, in which case the fitting may resemble a standard mains power plug. Alternatively, the input terminals may be provided on a mains plug connected to the housing by a cable, so that the fitting resembles a power extension lead.

In some of these examples, the fitting may simply be plugged into a power socket without any rewiring of the house's electrical system being required. In other examples, the fitting may simply be used to replace an existing fitting, such as a power outlet socket or ceiling rose, without any changes to the house's electrical system being required other than to connect existing cables to the fitting. In further examples, the fitting may be used to replace an existing fitting but may require some modification of the house's wiring system, for example to replace a two core (live and switched live) and earth cable to a light switch with a three core (live, switched live and neutral) and earth cable.

Methane (as currently supplied by the gas main in the United Kingdom) is less dense at room temperature and pressure than air. In the event that leaked methane stratifies in a room, the gas detector is best sited at or near ceiling level. Conveniently, with normal wiring practice in the United Kingdom, ceiling roses have permanently live, neutral and earth lines running to them so that no additional cabling is required.

On the other hand, butane, propane and liquefied petroleum gas (LPG) (as sometimes supplied in gas bottles or from gas tanks) are more dense at room temperature and pressure than air. In the event that these gases leak and stratify in a room, the gas detector is best sited at or near floor level. Conveniently, with normal wiring practice in the United Kingdom, wall mounted power sockets just above the skirting board have permanently live, neutral and earth lines running to them so that again no additional cabling is required.

Specific embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of a gas detection unit; Figure 2 is a schematic circuit diagram of a conventional electricity supply to a house and a distribution board; Figures 3A-C are a front view, side view and rear view, respectively, of a gas detection unit mounted on a plain plate; Figures 4A & B are a front view and rear view, respectively, of a gas detection unit incorporated into a lighting wall switch; Figure 5 is a front view of a gas detection unit incorporated into a different lighting wall switch; Figures 6A & B are a front view and rear view, respectively, of a gas detection unit incorporated into a socket outlet; and Figures 7A-7C are front side and rear views, respectively, of a gas detection unit resembling a mains plug.

Referring to Figure 1, a gas detection unit 10 has live, neutral and earth connection terminals 12L,12N,12E for connection to a mains electricity supply. The live and neutral terminals 12L, 12N are connected to the AC inputs of a power supply circuit 14, which produces a regulated low-voltage DC output which powers a gas detector 16, a preset voltage divider 18 and a comparator 20. The more negative output of the power supply circuit 14 is also connected to the earth terminal 12E. The gas detector 16 produces an analogue output signal which is approximately linearly related to the concentration of particular combustible hydrocarbon gases in the surrounding atmosphere. The gas detector may be an off-the-shelf item, such as "CII-D3" combustible gas pellistor produced by Alphasense Limited, CM77 7AA, United Kingdom.

That gas detector 16 is responsive to hydrogen, methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, ethane, acetylene and isobutylene. The output of the gas detector 16 is supplied to the non-inverting input of the comparator 20, and the voltage divider supplies a preset voltage to the inverting input of the comparator 20. The output of the comparator 20 therefore swings high when the concentration of hydrocarbon gases in the surrounding atmosphere exceeds a threshold set by the voltage divider 18. The threshold is chosen such that the concentration is significant, but is not so large that there is a serious risk of explosion. The output of the comparator 20 is supplied to a control input of a controllable switch 22 which can connect the live terminal 12L to the earth terminal 12E via a resistor 24.

The controllable switch 22 may be of any suitable type such as a relay, a transistor, a thyristor or a triac. The switch closes when the output of the comparator 20 swings high. The value of the resistor 24 is chosen so that, when the switch is closed, a sufficient current flows between the live and earth terminals 12L, 12E to trip a residual-current circuit-breaker (RCCB or RCD) or earth-leakage circuit-breaker (ELCB) in the mains supply circuit. For example, with a 230V supply voltage, a controllable switch 22 in the form of a relay having substantially zero contact resistance when closed and a 3OmA RCCB, the value of the resistor 24 required to trip the RCCB is 230V/ 3OmA = 7.7 kilohms, and so the resistor may be chosen to have a value of 4.7 kilohms. It will be appreciated that such a resistor would need to have a power rating of about 11W if the mains voltage were applied to it continuously. However, since the resistor 24 passes current for only a fraction of a second between closure of the switch 22 and tripping of the RCCB 38, the resisitor 24 may have a far lower power rating, such as W. Referring to Figure 2, in a typical single-phase electricity supply system for a house in the United Kingdom, mains electricity is received from a two-core (live and neutral) supply cable 26 having an earthed sheath 27. The neutral supply 28 is connected via an electricity meter 30 to a distribution box 32. The live supply 34 is connected via a company fuse 36 and the meter 30 to the distribution box 32. In the distribution box 32, the live and neutral supplies are connected to one or more RCCBs 38, two being shown in Figure 2. The live output from each RCCB 38 is connected to one or more miniature circuit breakers (MCB5) 40 in the distribution box 32, two being shown for each RCCB 38 in Figure 2. Each ring 42 or other circuit of the house's wiring system has its live end(s) connected to the live output of a respective one of the MCBs 40, its neutral end(s) connected to the neutral output of the respective RCCB 38, and its earth end(s) connected to an earth busbar 44 which is connected back to the earthed sheath 27 of the cable 26.

Each MCB 40 trips (i.e. serves to disconnect the live conductors of the respective ring 42 or other circuit from the live supply 34) in the event that the current flowing in the live supply 34 so that the respective ring 42 or other circuit exceeds the rating of the MCB 40.

Each RCCB 38 trips (i.e. serves to disconnect the live and neutral conductors of the ring(s) 42 or other circuits connected through that RCCB 38 from the live and neutral supplies 34,28) in the event that the difference between the live current and the neutral current flowing through that RCCB 38 exceeds the rating of the RCCB 38. A typical trip rating for domestic RCCBs 38 in the United Kingdom is 3OmA. Such a difference between the live and neutral currents arises primarily if the respective ring 42 or other circuit has a leakage path from live to earth, but may also arise in three-phase installations if there is a leakage path between one phase and another.

Referring back to Figure 1, it will be appreciated that when the gas detection unit 10 is connected to one of the rings 42, in the event that the controllable switch 22 closes due to the detection of gas by the gas detector 16, it will cause the RCCB 38, to which that ring 42 is connected, to trip. Accordingly, it will no longer be possible for any typical apparatus connected to that ring 42 to cause a spark which may ignite the gas.

Depending on where gas pipes and appliances are located in a house, it may be desirable to connect more than one gas detection unit 10 to a ring or rings 42 served by the same RCCB 38. In the case where a house has more than one RCCB 38, depending on where gas pipes and appliances are located in a house and where the rings 42 run, it may be desirable to connect one or more gas detection units to rings 42 served by different RCCB's 38.

Various ways of conveniently disposing gas detection units 10 in the house will now be described with reference to Figures 3A to 7C.

Figures 3A-C shows a fitting 45 with the gas detection unit 10 built onto a printed circuit board (PCB) 46 and mounted behind a faceplate 48 designed to fit a standard single pattress box. The faceplate 48 is perforated so that gas can reach the gas detector 16 located behind the perforations. The three terminals 12L,12N,12E are mounted on the PCB 46. A pattress box can therefore be fitted to a wall beside an existing electrical fitting such as a light switch or a power socket. The gas detection unit 10 is then electrically spurred to the live, neutral and earth terminals of the existing fitting, and the fitting 45 is then attached to the pattress box.

Figures 4A & B show a fitting 50 with the gas detection unit 10 similarly mounted behind one half of a faceplate 52 designed to fit a standard double pattress box. A light switch 54 is mounted behind the other half of the faceplate 52 and has it rocker 56 protruding through the faceplate 52. The live terminal 12L of the gas detection unit 10 is connected to the permanently live connection 58 of the light switch 54. In the case where the light switch 54 is of the one-way type, it will be appreciated that the fitting 50 will need to be connected to one or more cables having an earth conductor and three cores for (i) the permanently live connection to the gas detection unit 10 and the light switch 54, (ii) the neutral connection to the gas detection unit 10, and (iii) the switched live connection 57 to the light switch 54. In the case where the light switch 54 is of the two-way type, an additional core will be required for connection to the alternate switched live connection 59 of the light switch 54.

Figure 5 shows a fitting 60 that is similar to the fitting 50 of Figures 4A & B, except that the gas detector unit 10 is disposed towards one corner of the faceplate 62, and the faceplate 62 is designed to fit a standard single pattress box.

Figures 6A & B show a fitting 64 with the gas detection unit 10 mounted behind one half of a faceplate 66 similarly to Figures 4A & B. However, a switched 1 3A outlet socket 68 is provided on the other half of the faceplate 66. The socket 68 has live, neutral and earth input terminals 70L,70N,70E which are connected to the live, neutral and earth terminals 12L, 12N, 12E, respectively of the gas detection unit 10. The socket 68 also has a live output terminal 71L which is connected to the live input terminal 70L via a switch 69, and neutral and earth output terminals 71N,71E which are permanently connected to the neutral and earth input terminals 70N,70E, respectively. It will be appreciated that the fitting 64 does not require any additional cabling compared with a conventional outlet socket.

Figures 7A-C show a gas detection unit 10 built into a device 72 having a housing 74 and pins 76L,76N,76E and resembling a 13A three-pin plug. The gas detector 16 is mounted behind a perforated wall of the housing 74. The live, neutral and earth terminals 12L, 12N, 12E of the gas detector unit are connected to the live, neutral and earth pins 76L,76N,76E. It will be appreciated that the device 72 will be effective only if it is plugged into a socket which is fed via a RCCB 38 and, if the socket is a switched socket, only if the socket is switched on.

Nevertheless, the device 72 does not require any specialist wiring by the installer.

It will be appreciated that many modifications and developments may be made to the embodiments of the invention described above.

For example, the gas detection unit 10 may be built into other fittings such as a ceiling rose or a housing at the end of a flying lead having a mains plug at its other end.

The perforations shown in the drawings may be provided other than on the face of the faceplate. For example, perforations may be provided in the lower and upper edges of the faceplate.

The gas detection unit 10 may be provided with one or more indicators or alarms. For example, it may have a viewable green LED which is illuminated when the gas detection unit is monitoring. It may have a red LED or an audible beeper which is activated when the gas detector detects gas, being powered for example by a storage capacitor in the gas detection unit.

The resistor 24 in the gas detection unit 10 may have different values for use with RCCBs 38 having different trip ratings.

The gas detection unit 10 may be provided with a manually operable test switch which, when operated, causes the controllable switch 22 to close so that it can be checked that the RCCD 38 does indeed trip.

The gas detection unit 10 may be battery operated, in which case a connection of the gas detection unit 10 to the neutral line is not required.

The gas detector unit may be employed in electricity supply systems having different forms of leakage fault circuit breakers.

As suggested in the introduction of this description, the detector 16 of the detector unit may alternatively, or additionally, be responsive to: the concentration of particular hydrocarbon gases in the atmosphere surrounding the detector exceeding a predetermined value; the concentration of carbon monoxide gas in the atmosphere surrounding the detector exceeding a predetermined value; the concentration of carbon dioxide gas in the atmosphere surrounding the detector exceeding a predetermined value; the relative humidity of the atmosphere surrounding the detector exceeding a predetermined value; the temperature of the detector exceeding a predetermined value; and/or the level of infra-red radiation falling on the detector exceeding a predetermined value.

It should be noted that the embodiments of the invention have been described above purely by way of example and that many other modifications and developments may be made thereto within the scope of the present invention.

Claims

-10 -CLAIMS(The reference numerals in the claims are not intended to limit the scope of the claims.) 1. A detection unit (10), comprising: a detector (16) for detecting the presence of a predetermined feature of the ambience of the detector; a live input terminal (12L) for connecting the unit to a live line of a mains electricity supply protected by a residual-current or earth-leakage circuit-breaker (38); an earth input terminal (12E) for connecting the unit to an earth line of the mains supply; and a controllable switch (22) responsive to the detection of the predetermined feature of the ambience to complete a circuit (22,24) between the live and earth connectors.
2. A detection unit as claimed in claim 1, wherein: the controllable switch is of a type that, when operated, does not produce sparks accessible to the atmosphere.
3. A detection unit as claimed in claim 1 or 2, wherein: the completed circuit is arranged to pass a current of at least 3OmA between the live and earth terminals when the live terminal is at the nominal mains voltage relative to the earth terminal.
4. A detection unit as claimed in claim 1 or 2, wherein: the completed circuit is arranged to pass a current of at least 1A between the live and earth terminals when the live terminal is at the nominal mains voltage relative to the earth terminal.
5. A detection unit as claimed in any preceding claim, wherein: the controllable switch is arranged to complete the circuit through a resistor (24).

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6. A detection unit as claimed in any preceding claim, wherein the detection unit is responsive to at least one of the following: the concentration of particular hydrocarbon gases in the atmosphere surrounding the detector exceeding a predetermined value; the concentration of carbon monoxide gas in the atmosphere surrounding the detector exceeding a predetermined value; the concentration of carbon dioxide gas in the atmosphere surrounding the detector exceeding a predetermined value; the relative humidity of the atmosphere surrounding the detector exceeding a predetermined value; the temperature of the detector exceeding a predetermined value; the level of infra-red radiation falling on the detector exceeding a predetermined value.
7. A detection unit as claimed in any preceding claim, wherein: the detector is electrically powered; and the unit further includes a battery for powering the detector.
8. A detection unit as claimed in any preceding claim, further including: a neutral input terminal (12N) for connecting the unit to a neutral line of the mains supply.
9. A detection unit as claimed in claim 8, wherein: the detector is electrically powered; and the unit further includes a power supply circuit (14) for taking power from between the live and neutral input terminals and supplying power to the detector.
10. An electrical fitting (45;50;56;64;72) having: a detection unit as claimed in any preceding claim.

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11. An electrical fitting (68) as claimed in claim 10 when dependent on claim 8 or 9, further including: live, neutral and earth output terminals (71L,71N,71E) connected to, or switchably connected to, the live, neutral and live input terminals for connection to a mains plug.
12. An electrical fitting (45;50;56;64) as claimed in claim 10 or 11, wherein: the fitting further includes a plate (48;52;62;66) for mounting on a mounting box so that the gas detector, input terminals and controllable switch are disposed inside the mounting box; and the plate is permeable to the ambience.
13. An electrical fitting (45;64) as claimed in any of claims 10 to 12, further including: a switched-live output terminal (57;7 1L); and a manually operable switch (54;69) for connecting the live input terminal to the switched live output terminal.
14. An electrical fitting (72) as claimed in claim 10, wherein: the fitting includes a housing (74) containing the detector and the controllable switch; the housing is permeable to the ambience; and the input terminals (76L,76N,76E) are provided externally of the housing.
15. An electrical fitting as claimed in claim 14, wherein: the input terminals (76L,76N,76E) are mounted on and project from the housing for insertion into a mains outlet socket.
16. An electrical fitting as claimed in claim 14, wherein: the input terminals are provided on a mains plug connected to the housing by a cable.

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17. A detection unit or electrical fitting, substantially as described with reference to the drawings.
18. A building having: a mains electrical system including a residual-current or earth-leakage circuit-breaker (38) and mains distribution cables (42) extending from the circuit-breaker; and at least one detection unit or electrical fitting as claimed in any preceding claim connected to such a mains distribution cable.