GB2539164A

GB2539164A - Protective master switch

Info

Publication number: GB2539164A
Application number: GB1502634.7A
Authority: GB
Inventors: Radford Alan; Wedlake Ian
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-02-17
Filing date: 2015-02-17
Publication date: 2016-12-14
Also published as: GB201502634D0

Abstract

A master switch 3 is provided for installation between a metered incoming electrical supply L, N and one or more electrical supply units such as consumer units 5, 6. The master switch 3 includes an isolation switch 4, e.g. an RCD, which is both manually and electrically operable. Inside the master switch there is an electronic protection circuit which has a first input arranged to receive input signals from at least one fume detector 12 installed in the electrical supply units 5, 6, and a second input to receive input signals from a room smoke detector system 8-10. The electronic protection circuit is arranged to electrically operate the isolation switch 4 in response to a signal from one of the fume detectors 12. In the event of the smoke detector system being triggered a signal at the second input operates via a time delay to produce delayed operation of the isolation switch 4.

Description

PROTECTIVE MASTER SWITCH

TECHNICAL FIELD OF THE INVENTION

This invention relates to a protective master switch for use in electrical supply installations.

BACKGROUND

In new electrical supply installations it is normal for the supply company to provide the incoming supply with a master fuse followed by a meter, both of which are the responsibility of the company. On the customer's side of the meter there is normally a master switch which can be used to electrically isolate the installation in the event of an emergency, followed by a variety of electrical supply units such as one or more consumer units, distribution boards, wall sockets and other power outlets, extension sockets, junction boxes, light switches and ceiling roses for example.

Electrical supply units such as consumer units are sometimes subject to overheating. As such devices age the risk tends to -2 -become greater due to an increase in electrical resistance caused by oxidation of electrical contacts, or loss of resilience in spring contacts.

Patent specification No. GB 2 446 186 A describes an electrical safety device which includes a thermal switch arranged to provide a leakage current to earth to activate a remote residual current device (RCD). The switch also triggers a thyristor latch that operates a warning device. In GB 2 474 245 A it is proposed that the electrical supply unit incorporates a two stage safety device that operates at different temperatures. A temperature-operated latch responds when the temperature within the housing exceeds a first threshold by activating a warning device. If the temperature should exceed a higher second threshold a thermal switch produces a current flow into the earth or neutral line to activate the RCD and thereby electrically isolate the unit from the incoming supply. The latch does not reset automatically if the temperature falls, so that the warning device continues to operate to alert people to the fact that an alarm condition has occurred.

Whilst such safety devices are very effective under many conditions which give rise to overheating it has been found that when conditions occur which cause an electrical connection to overheat the temperature of the connection will often rapidly increase to dangerously high temperatures while the overall temperature of the unit is still close to ambient. The cost of providing all the electrical supply units in an installation with multiple temperature sensors is prohibitive, and the siting of the -3 -sensors is therefore a compromise.

US 2010/0 073 841 Al discloses a fire protection system for electrical supply installations. Various detectors provide low level outputs if subjected to gas, smoke or heat exceeding a first threshold and provide a high level output if a second threshold is exceeded. Different circuits breakers are triggered by the low level and high level outputs.

The present invention seeks to provide a new and inventive way of providing an electrical supply installation with inexpensive, easily installed, yet comprehensive protection against overheating and fire.

SUMMARY OF THE INVENTION

The present invention proposes a protective master switch for installation between a metered incoming electrical supply and one or more electrical supply units, including: a) an isolation switch to isolate the electrical supply units from the incoming electrical supply, said isolation switch being both manually and electrically operable; and b) an electronic protection circuit having: - a first input to receive input signals from at least one fume detector installed in one or more of said electrical supply units, - a second input to receive input signals from a room smoke -4 -detector system, - a first output arranged to electrically operate said isolation switch to isolate the electrical supply units, said first output being arranged to be activated in response to a signal at said first input from said fume detector or detectors; and - a time delay arranged to produce a delayed output signal at said first output to produce delayed operation of said isolation switch in response to a signal at said second input from said room smoke detector system.

The invention also provides a protective master switch for installation between a metered incoming electrical supply and one or more electrical supply units which has an output to activate a telephone dialing system.

The invention also provides a protective master switch for installation between a metered incoming electrical supply and one or more electrical supply units which has an output to trigger a room smoke detector system.

The invention also provides a protective master switch for installation between a metered incoming electrical supply and one or more electrical supply units which incorporates an electrically operable residual current device (RCD).

BRIEF DESCRIPTION OF THE DRAWINGS -5 -

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is a block diagram of an electrical supply installation incorporating a protective master switch in accordance with the invention; Figure 2 is a more detailed diagram of the protective master switch; and Figure 3 is schematic diagram of a fume detector for use with the protective master switch.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring firstly to Fig. 1, a typical up-to-date electrical supply installation has an incoming single phase electrical supply (e.g. 240v AC, 50 Hz) designated L N. The supply company has provided the incoming supply with a master fuse 1 followed by a meter 2, both of which are the responsibility of the supply company. On the customer's side of the meter there is usually a simple master switch which can be used to electrically isolate the installation in the event of an emergency, but in the present invention this is replaced by a new protective master switch 3 having the usual manually operable isolation switch 4 to isolate -6 -the electrical supply units from the incoming electrical supply. The switch 3 is followed by a variety of electrical supply units such as one or more consumer units 5, 6 (two being shown by way of example), distribution boards, wall sockets and other power outlets, extension sockets connected to a mains supply via a cable and plug, junction boxes, light switches and ceiling roses for example, none of which is specifically shown in the drawing.

As with most new build properties or extensions, the building is protected by a fire alarm system which comprises a main control box 8 and a number of room smoke detectors such as 9, 10. The control box 8 is wired to operate an internal and/or external warning device 11, as required.

In order to protect against the possibility of an overheat situation or fire developing in one or more of the aforementioned electrical supply units, each unit may be provided with an internal fume detector 12, which for purposes of illustration are shown in both consumer units 5 and 6. The fume detectors are connected to the protective master switch 3 via inconspicuous small gauge wiring 13. A further wired connection 14 is made from the alarm output of the fire alarm control box 8 and the protective master switch 3. In addition, the switch 3 may have an optional line connection 15 to an external telephone line or a dialing unit for initiating a call via a mobile telephone network.

Referring to Fig. 2, the isolation switch 4 of the protective master switch 3 is connected in line between the incoming and outgoing -7 -supply lines L and N. The master switch may typically be a 100 amp RCD with 300 mA trigger current, a manually operable MCB or the like. As is well known in the art, a magnetic circuit breaker (MCB) is a resetable fuse which opens when an excessive current flows. These may typically incorporate a solenoid which opens a pair of contacts if a high enough current flows. A residual current device (RCD) is a device which breaks a circuit in response to an imbalance in the current flowing through a pair of lines (e.g. live and neutral). These include earth leakage circuit breakers (ELCBs). The important thing is that the isolation switch 4 is both manually operable and capable of being electrically triggered to isolate the outgoing supply lines to the consumer units etc. The consumer units 5 and 6 may also incorporate an RCD 16, but this would typically be rated at 80 amps with 30 mA trigger current so that an overload in one of the protected circuits will trigger the RCD in the consumer unit before the RCD in the master switch 3.

The protective master switch 3 also incorporates an electronic protection circuit 18 having a first input 19 to receive electrical signals from the fume detectors 12. A second input 20 receives input signals from the fire alarm 8 via connection 14 in response to activation of a room smoke detector 9, 10. An input signal at the second input 20 triggers a time delay module 28.

The protection circuit 18 also provides a first output 21 at which an electronic activation signal can be sent to the isolation switch 4 to trigger the switch and isolate the supply lines. A second output 22 may also trigger a telephone call to a pre-programmed destination -8 -via the line connection 15.

In the event that one of the fume detectors 12 is triggered, a signal arriving at the first input 19 causes the protection circuit 18 to immediately send a signal to the first output 21 to trigger the isolation switch 4. This ensures that power to the electrical supply units is cut immediately, which is likely to terminate the overheat condition.

In the event that the fire alarm 8 is activated by one or more of the smoke detectors 9, 10 an input signal arriving at the second input 14 will trigger the time delay module 28 which, after a pre-programmed time delay, produces an output signal at the first output 21. The time delay will typically be between one minute and five minutes such that, in the event of a fire, the occupants will be able to evacuate the building before the power is cut. Removal of the power, after allowing time for evacuation under electric light if a fire starts at night, ensures that the fire services can begin the task of extinguishing the fire without having to locate the master switch and cut off the electric supply before using water hoses, thus gaining valuable time in starting to fight the fire.

Whenever the master switch is triggered an indicator light 25 may be illuminated (Fig. 1) to inform users that activation of the protective master switch has caused the power outage rather than an external power supply failure. The protection circuit may also initiate a telephone call via the second output 22 and line -9 -connection 15 to advise interested parties of the condition. It is also possible to raise an alert at a remote location by using a message generating device which is programmed to send a text message via a cellular telephone network to a predetermined number, or numbers, when the protection circuit is triggered, whether by one of the fume sensors 12 or by the fire alarm 8.

The protection circuit 18 also has a third output 23 which can be wired to a trigger input of the fire alarm 8 via a further connection 24 (Fig. 1). If one of the fume detectors 12 is triggered a signal will immediately be sent to the fire alarm via the third output 23 to set off the fire alarm.

Fig. 3 shows a typical fume detector 12 which can be used in the electrical supply units, namely an ionisation detector. A pair of mutually spaced plates 30 and 31 are subjected to a DC potential difference 32 and an alpha particle emitter 33 is arranged such that the emitted alpha particles cause ionisation of the air molecules (nitrogen and oxygen) between the two plates. These ions are attracted to the plates of opposite polarity causing a current to flow which is sensed by a current measuring device 34. If certain airborne substances such as fumes or smoke particles enter the gap between the plates the ions are disrupted before they reach the plates resulting in a drop in current which in turn triggers an output from the detector.

Consumer units are generally designed for normal working temperatures up to about 105 degrees Celsius. PVC sheathing -10 -used on electrical wires will generally start to emit fumes and gases at 120-130 degrees Celsius and will then begin to emit smoke at 150-170 degrees Celsius as they begin to ignite. Ionisation detectors will detect fumes and trigger the protection circuit well before ignition of the consumer unit wiring. In the unlikely event that the fumes do not trigger the detector 12 the emission of smoke particles will undoubtedly activate the detector and trigger the protection circuit. This two-stage process makes the system extremely reliable and will, in most cases, operate well before a fire begins.

As an additional feature, a plug-in message generating device may be provided which is inserted into a wall socket and sends a text message in response to a power failure to alert someone to the fact that the protective master switch may have been triggered. The device can also be programmed to send an appropriate text message to the recipient/s when power is restored, e.g. if a re-connection is made after a short power cut.

Whilst the above description places emphasis on the areas which are believed to be new and addresses specific problems which have been identified, it is intended that the features disclosed herein may be used in any combination which is capable of providing a new and useful advance in the art.

Claims

CLAIMS1. A protective master switch for installation between a metered incoming electrical supply and one or more electrical supply units, including: a) an isolation switch to isolate the electrical supply units from the incoming electrical supply, said isolation switch being both manually and electrically operable; and b) an electronic protection circuit having: - a first input to receive input signals from at least one fume detector installed in one or more of said electrical supply units, - a second input to receive input signals from a room smoke detector system, - a first output arranged to electrically operate said isolation switch to isolate the electrical supply units, said first output being arranged to be activated in response to a signal at said first input from said fume detector or detectors; and - a time delay arranged to produce a delayed output signal at said first output to produce delayed operation of said isolation switch in response to a signal at said second input from said room smoke detector system.
2. A protective master switch according to Claim 1 which includes a second output to activate a telephone dialing system in response to a signal at said first or second input.

-12 -
3. A protective master switch according to Claim 1 or 2 in which the electronic protection circuit has a third output to trigger the room smoke detector system when an input signal is received at the first input.
4. A protective master switch according to any preceding claim which incorporates an electrically operable residual current device (RCD).
5. A protective master switch substantially as described with reference to the drawings.