GB2446186A - Electrical safety device - Google Patents

Abstract

The device gives a clear visual and audible warning of over heating within electrical installations. The device detects excessive heat that may be due to arcing and poor connections, and that can cause an electrical fire. The device may comprise a thermal switch that operates at an undesirable temperature, an audible warning such as buzzer 4, a visual alarm such as LED 1, a reset button 2 allowing the device to be reset without replacing components, and a functionality test button 3. The device may be powered by a battery (fig 1, 7) and the circuitry (fig 1) may comprise a latching thyristor and can provide a leakage current to earth to activate a residual current device (RCD). An alternative version is shown (fig 5) for circuits such as lighting that are not protected by a RCD and requires no connection to the mains. The device may be installed in a power outlet, a shower isolation switch (fig 3) a spur unit (fig 4), or a ceiling rose (fig 6).

Description

Electrical Safety Device This invention is a device that gives an early

warning of over heating within electrical installations.

Poor connections within electrical installations often cause arcing and excessive heat which is the main cause of electrical fire. This device warns of excessive heat before such a level as that to cause fire.

The invention comprises of a thermal switch that is used to activate an alarm when reaching an undesirable temperature. The alarm is made up of a latching circuit with battery supply which will give an audible and visual warning. It can also be used to apply an earth current for RCD (Residual Current Device) activation.

The device gives a clear audible and visual warning so that occupants know of the occurrence of a heat related electrical fault. The battery supply means that it does not rely on any external power supply so can be incorporated into all electrical installations. The visual warning also gives an indication of which installation has developed a fault allowing easier fault finding. These two functions, due to the battery supply will continue to give an indication even after any power isolation.

Examples of the invention will be explained with reference to the following drawings: Examples with the addition of RCD activation circuit Figure 1: circuit used for device with RCD circuitry.

Figure 2: use with 13 amp power outlet; Figure 3: shower isolation switch; Figure 4: 13 amp spur unit.

Examples of device with only warning system (non RCD circuits) Figure 5: circuit used for warnrng device.

Figure 6: use with lighting ceiling rose; Figure 7: light switch.

For the full device the circuit in figure 1 would be used, it shows in the first part of the circuit (1) how the device when operated by the thermal switch (3) how it places a small current leak to earth to activate the RCD and gives a bias current to the thyristor in the alarm part of the circuit (2). The second part of the circuit (2) is a thyristor based latchmg circuit which when activated will continue to operate after the activation current is removed. The circuit produces a visual warning via a Light Emitting Diode (5) and an audible warning through a sounder within the device (6). The batteries (7) are used to provide a power source for alarm even after the mains power has been removed.

The alarm is cancelled by a push button (8) which removes the supply to the thyristor which resets its latching state. The circuit can be tested by using the push button (4) which imitates the switching of the thermal switch.

Figures 2, 3 and 4 show possible incorporations of the above circuit within a 13 amp power outlet, shower isolation switch and 13 amp spur unit. All figures show locations of the alarm LED (1), sounder (4) and reset (2) / test (3) buttons. The test and reset buttons do not extrude the casing so that a small point would be required to operate them; this avoids accidental depressing. Also shown on these figures is the positioning of the battery container (5) which would be accessible from outside the unit so that it does not need to be removed to have the batteries replaced.

A modified circuit is shown in figure 5 which can be used within installations which are not protected by a RCD i.e. lighting circuits.

This circuit does not require connection to the mains because it is not used to operate the RCD. The thermal switch (I) is only used to provide a bias current to activate the alarm. Again it has its power provided by internal batteries (4). It also gives ard audible and visual warning of activation via a IED (2) and soimder (3) as well as the push buttons to reset (5) and test (6) the alarm.

Figures 6 and 7 show how the circuit mentioned above could be incorporated into a lighting ceiling rose and light switch. These figures show the positioning of the LED (1), sounder (4), test (3) and reset (2) buttons. The battery container (5) would again be externally accessible and the push button would not extrude the casing.

Claims (8)

1. Claims I. A device giving clear warning of over heating within

   electncal mstallations.
2. 2. A device according to claim I, where heat detection is made by thermal switch operating at the undesired temperature.
3. 3. A device according to claim 2, in which the clear warning is made by a clear visual and audible warning.
4. 4. A device according to claim 2, but also providing earth current to operate a Residual Current Device.
5. 5. A device according to claim 3, where the visual and audible warning is made via a Light Emitting Diode and Sounder.
6. 6. A device according to claim 2, which is battery backed so that to continue to operate after power isolation.
7. 7. A device according to claim 2, which can be reset after activation, without the need to replace components.
8. 8. A device according to claim 2, which has a testing facility to test functionality.