Note: Descriptions are shown in the official language in which they were submitted.
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Electrical switch board smoke detector unit
Field of Invention
This invention relates to disconnection of electrical supply in buildings and
in
electrical switch boards, when potential fire is detected. However the
invention is not limited to switch board fires or faults.
Background
Smoke alarms are common in both residential and commercial buildings.
However, they merely warn of a fire and do nothing to disconnect electrical
power. Many fires are caused by electrical products, either due to failure or
inappropriate positioning or use. For example, an electric heater may be
covered or knocked over or hard wired items, such as an electric stove, may
cause a fire.
If no one is present then no action will probably occur. With electrical
items,
power will remain supplied until the electrical item is sufficiently damaged
that a short circuit of some form occurs, tripping a fuse, circuit breaker
(CB)
or Residual Current Detector (RCD). However, by this stage a fire will usually
have been established and be self fuelling - removing the electrical supply
will
not help.
In addition, electrical faults are a relatively common occurrence in
electrical
switch boards. These are typically located outside of a building or in a
wiring
closet. If the switch board is outside, an internal smoke detector will not
detect the smoke generated by a switch board fault. If the switch board is in
an internal wiring closet, a fire may be established before sufficient smoke
escapes the closet to be detected. Further, whether inside or outside a
building, a fire in a switch board can easily penetrate into roof spaces or
internal cavities because the electrical wires inherently breach any fire
walls
or other barriers that impede spread of fire.
Summary of the Invention
In an attempt to ameliorate at least some of the disadvantages of existing
systems the present invention provides a module for mounting on an electrical
switch board. The module is connected to one or more smoke detectors and is
activated when a smoke detector activates.
The module may be mounted next to existing circuit breakers and when
activated mechanically flips the circuit breaker lever of one or more adjacent
circuit breakers to an open position, thereby disconnecting the power supply
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to the relevant circuits. Thus the module may be retrofitted to an existing
switch board.
The module may incorporate a circuit breaker, such that it does not take up
an additional place in a switch board. Such an embodiment is of particular use
for new installations or installations where switch board space is limited.
A smoke detector may be located on or adjacent the switch board, such as in
the switch box or wiring closet, for detecting of switch board faults.
Alternatively or in addition, a smoke detector located within the building may
be connected to the module. Embodiments may have the smoke detector
incorporated into the module itself.
A single module may be connected to more than one smoke detector.
Similarly, a single smoke detector may be connected to more than one
module. This may occur where the physical positioning of circuit breakers may
require multiple modules, such as when located on different rails of a switch
board.
The use of a separate module to mechanically switch appropriate circuit
breakers means that no modifications need to be made to the electrical
circuits protected by the adjacent circuit breakers.
Brief Description of the Drawings
Figure 1 shows a schematic layout of part of a switch board and part of
building including a module according the invention.
Detailed Description of Preferred Embodiment
Referring to the drawings there is shown a switch board 10 having two circuit
breakers 12, 14 mounted on the board. Typically the circuit breakers 12 are
mounted on the board via a DIN rail 16. The circuit breaker 12 may be a main
switch, a RCD or a normal circuit breakers controlling supply of power to a
separate electrical circuit 18. In the embodiment circuit 18 supplies power to
a general power outlet (GPO) 20 in building 22 but may supply hard wired
item, such as a stove.
Mounted adjacent the circuit breaker 12 is a module 24 according to the
invention. The module 24 is sized to take up the space of a standard single
pole circuit breaker and is designed to mount on the din rail 16, but this is
not
critical. The module 24 has a drive arm 26 that extends sideways and above
the reset arm 28 of the adjacent circuit breaker 12. The drive arm 26 may
extend in both directions and may extend over more than one circuit breaker.
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Thus, for example, the drive arm 26 could extend over the reset arm 30 of
circuit breaker 14 and any circuit breakers located to the left of the module.
The reset arms 28, 30 of the circuit breakers are shown in the "power on"
position and move downwards to break the circuit. The location of the drive
arm 26 above the reset arms 28, 30 thus does not prevent each individual
circuit breaker activating in an overload situation. Thus tripping of a
circuit
breaker due to a fault in the circuit will not cause drive arm 26 of module 24
to move and trip any other circuit breakers. Nor does the drive arm 26 prevent
or limit the ability of a user to reset the individual circuit breaker to the
power on position after the circuit breaker has "tripped".
The module's drive arm 26 is driven by a conventional circuit breaker solenoid
mechanism. The specific drive mechanism is not critical. However, activation
of the mechanism is in response to a signal from one or more smoke detectors
32 rather then excess current in a circuit. In the preferred installation a
smoke
detector 32 is located in the switch board enclosure and connected to the
module by signal wires 34. However, the smoke detector may be remote from
the switch board enclosure, such as within the building, as indicated by smoke
detector 36. Multiple smoke detectors may be connected to a single module.
Thus smoke detectors 32 and 36 may be simultaneously connected to the
module 24. Thus, in the embodiment shown internal smoke detector 36 may
supply an activation signal via wire 38 to input/output 40. As seen, the
module
24 also has un-powered auxiliary contacts 42 and 44 that are closed when the
module 24 is in a fault position. These may be used to communicate a fault
state or position to a monitoring system.
Each smoke detector may be connected to more than one module, with all
connected modules being activated by the one smoke detector. Multiple
smoke detectors may be connected to multiple modules, whereby each
module may be activated by one or a number of smoke detectors.
As an example if the switch board has multiple DIN rails populated by circuit
breakers a module may be located on each DIN rail but connected to a single
smoke detector.
Any smoke detector is preferably mains powered with a back up power source
(battery, capacitor etc) and is more preferably a photo detector type smoke
detector, rather than an ionising type detector. However, the specific type of
smoke detector is not critical.
The module is supplied with powered via live and neutral wires 46. In the
preferred embodiment these supply power for the drive mechanism for the
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drive arm 26 and the switch board detector 32. The module may also be a
circuit breaker or a RCD wired in a conventional manner. In such a
configuration there will be two ways of activating the drive mechanism for the
drive arm 26 - one will be via any connected smoke detector and the other via
conventional circuit breaker current detection.
Referring to the drawings, there is shown an electric heater 50 connected via
GPO 20 to circuit 18 controlled by circuit breaker 12. Due to a fault the
heater
50 is emitting smoke and fumes, indicated by 52. Before any fire becomes self
fuelling the smoke detector 36 detects the smoke and fumes and activates,
sending a signal to the module 24 via line 38. Modern hard wired smoke
detectors have an interconnect that is used to trigger other smoke alarms.
This interconnect is used to send the signal via line 38.
In the preferred embodiment any activation signal sent via line 38 to the
module 24 does not cause immediate activation. Instead the module
preferable includes a time delay circuit and the module 24 activates only if
the signal is applied for a predetermined time. This period may be fixed or
may be installer (or user) adjustable.
The time delay is to prevent power being turned off immediately for an
internal smoke generating event and to only turn the power off if the event
continues beyond a set period. As an example, if an occupant burns some toast
a kitchen smoke alarm may activate. The occupant is present to stop the
burning toast (or the automatic toaster stops of its own accord) and so the
source of the alarm ceases to exist. The smoke clears and the internal smoke
alarm stops within a short period of time. In these circumstances we do not
want the power to be cut immediately, due to the significant inconvenience
and possible danger at night that this may cause. However, if no one is
present
the source of smoke will, generally, continue to generate smoke and the
smoke alarm will continue to sound. After the preset period the module 24
activates, cutting power.
When the module activates, it drives drive arm 26 downwards. This causes
reset arm 28 of circuit breaker 12 to move to the power off position, thereby
removing power to circuit 18 and the heater 50 thereby removing the initial
heat source and preferably preventing a self fuelling fire from starting. This
all
occurs without any human involvement.
When any smoke and fumes have cleared, whether due to human intervention
of otherwise, the smoke alarm 36 ceases to activate and stops sending the
activation signal to the module 24. As with conventional circuit breakers, the
module does not reset and manual resetting is required. Resetting of the
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module 24 does not reset any tripped circuit breakers and so it is also
necessary to manually reset circuit breaker 12.
The operation with the smoke detector 32 located on the switch board or
within the switch board enclosure is substantially the same, and any smoke
and fumes detected by the smoke detector 32 will result in activation of the
module 24 and circuit breaker 12 as previously described. However, in this
case there is no time delay and a fault detected by the smoke detector 32 will
result in immediate activation of the module.
Whilst the circuit breaker 12 may be an ordinary circuit breaker supplying an
internal circuit, ideally a module connected to the smoke detector 32 will
trip
the main power switch/circuit breaker, thereby cutting power to all the
circuits connected to the switch board, irrespective of whether or not their
circuit is to blame. Thus a switch board fault will have all power removed and
not result in a fire.
The smoke detector 32 is preferably provided with a capacitor based backup
supply rather than a battery. This avoids the need for the occupant to
periodically replace a battery, since user manipulation of components in a
switch board is discouraged.
When the smoke detector 32 triggers and activates module 24, the activation
signal is sent via input/output 40 to any internal smoke detectors, such as
smoke detector 36. Thus any occupants of the building will be notified of the
switch board fault.
It will be appreciated that one module connected to the switch board smoke
detector 32 may activate the main circuit breaker whilst one or more modules
connected to internal smoke detectors may activate subsidiary circuit
breakers.
It will be apparent to those skilled in the art that many obvious
modifications
and variations may be made to the embodiments described herein without
departing from the scope of the invention. The scope of the claims should not
be limited by the preferred embodiments set forth in the examples, but should
be given the broadest interpretation consistent with the description as a
whole.
