WO2003061089A1

WO2003061089A1 - Safety device for electrical apparatus

Info

Publication number: WO2003061089A1
Application number: PCT/IT2003/000012
Authority: WO
Inventors: Lorenzo Limongiello; Teodoro Martino; Antonio Razionale
Original assignee: Lorenzo Limongiello; Teodoro Martino; Antonio Razionale
Priority date: 2002-01-18
Filing date: 2003-01-16
Publication date: 2003-07-24
Also published as: ITRM20020022A1; ITRM20020022A0; AU2003209680A1

Abstract

The invention concerns a safety device for at least one electrical apparatus (1), apt to be electrically supplied by a mains (4) through at least one power supply cable, comprising sectioning means (5) connected between the mains (4) and said power supply cable, having an open configuration, wherein said power supply cable is not applied, and a closed configuration, wherein said power supply cable is supplied, the safety device being characterised in that it comprises enabling means (2) controlled by switching means (3) and having a home configuration, wherein the enabling means (2) keeps the sectioning means (5) in the open configuration, and an enabled configuration, wherein the enabling means (2) controls the sectioning means (5) in order to make it assume the closed configuration, the switching means (3) being placed in correspondence with the electrical apparatus (1). This invention further concerns an electrical apparatus and the power cables provides with the components of the safety device.

Description

SAFETY DEVICE FOR ELECTRICAL APPARATUS

The present invention concerns a safety device for electrical apparatus, provided with power cable, which enables in a simple, reliable, and effective way to section the power supply off upstream the cable, the device being moreover simple to be realised and inexpensive.

The present invention further concerns an electrical apparatus and the power cables provided with the components of the safety device.

Domestic accidents caused by electric shock, during use of domestic apparatus supplied by the mains through a power cable, are very common. One of the most recurrent causes is the accidental fall of the domestic apparatus being used either onto conductive surfaces or into conductive environments. By way of illustration, a hairdryer or a radio falling onto a wet surface or into water, as for example in a bath or a sink, can cause very serious, often fatal, accidents to the user being in contact with the surface or the water.

Moreover, electrical apparatus even not operating, having the power switch in the off position, but having the supply plug inserted into the mains socket, are in any case supplied up to the power switch and, therefore, still present risks in case of fall onto conductive surfaces or into conductive environments.

In order to solve such problem, some safety devices have been developed.

Among these, the most used one is a differential switch incorporated into the supply socket, which is apt to detect a current leakage and consequently to cut off the power supply starting from the socket.

However, such safety device has some drawbacks.

First of all, since the differential protection is caused to operate only when a current leakage to ground occurs, and since in many world's countries the rules in force, such as the one of the Italian Electrotechnical

Commitee (CEI), forbid ground connection of apparatus lacking electrical ground connection (class II apparatus), the operation of safety differential switches is activated only after the leakage current has crossed the user, who allows the leakage circuit to be closed to ground.

Moreover, some scientific studies have shown that the differential switches are subject to operating defects, such as a lacking intervention at the first fault, a lacking intervention being not detected through the test button with which they are provided, an intervention beyond the calibration threshold and beyond the predetermined response time.

Still, in particular circuit condition, the protection given by the differential switch against direct contact may be partially or completely compromised. This is the case, for example, of a user in direct contact with the phase, the neutral and the ground. This condition may occur when the user picks up an electrical apparatus fallen in water. In fact, the leakage circuit comprises two meshes: the first mesh includes the user's arms and chest, while the second mesh includes the user's lower limbs contacting ground. Since only the current of the second mesh, which closes to ground crossing the user, may cause the intervention of the differential switch, as a consequence such an intervention could also lack, when the current of the second mesh is lower than the switch threshold one. However, the user is further crossed by the usually high current of the first mesh, which also involves the heart region. Therefore, in these circuit conditions, the lacking intervention of the differential switch does not protect the user from the great risks of electric shock.

It is therefore an object of the present invention to provide a safety device for electrical apparatus, provided with power cable, which enables in a simple, reliable, and effective way to section the power supply off upstream the cable when the apparatus is not correctly used.

It is still an object of the present invention to provide such a safety device which sections the power supply off upstream the cable in conditions of interruption of the same cable.

It is a further object of the present invention to provide such a safety device which is simple to be realised and inexpensive.

It is specific subject matter of this invention a safety device for at least one electrical apparatus, apt to be electrically supplied by a mains through at least one power supply cable, comprising sectioning means connected between the mains and said power supply cable, having an open configuration, wherein said power supply cable is not supplied, and a closed configuration, wherein said power supply cable is supplied, the safety device being characterised in that it comprises enabling means controlled by switching means and having a home configuration, wherein the enabling means keeps the sectioning means in the open configuration, and an enabled configuration, wherein the enabling means controls the sectioning means in order to make it assume the closed configuration, the switching means being placed in correspondence with the electrical apparatus.

Preferably according to the invention, the switching means comprises at least one button, connected through two electrical conductors to the enabling means, which is apt to assume alternatively a not operated position, corresponding to the home configuration of the switching means, or an operated position, corresponding to the enabled configuration of the switching means. The switching means, particularly the button, may be operated by the user of the electrical apparatus, such as in case of a hairdryer.

Alternatively, the switching means may be suitably operated by the weight of the electrical apparatus. For example, in case of a radio, the radio could be provided with a button at its base, which is kept pressed until the radio does not remain resting on the base. A mechanical system, placed within the radio, for locking the button, or a lock electronic system, placed within the socket, could further be provided, to avoid that, once the button rises due to an accidental fall of the radio, the same button could be pressed again and the power supplied reaches the radio in the case when the latter falls onto the supporting surface.

In a preferred embodiment of the device according to the invention, said two electrical conductors are short-circuited when the button assumes the operated position and are disconnected from one other when the button assumes the not operated position. In such a way, it is assured that in case of accidental cut of the power supply cable, which comprises said two electrical conductors, the power supply to the electrical apparatus is stopped upstream the power supply cable. Moreover, even in case of cut of an extension cable, the power supply to the electrical apparatus is stopped upstream the same extension cable. Always according to the invention, the enabling means may comprise current source means controlled by the switching means.

Still according to the invention, the enabling means may comprise the coil of at least one electromechanical relay, having N contacts and two positions, with N ≥ 1, preferably N = 2, said coil being connected to said current source means.

Further according to the invention, the sectioning means may comprise one or more switches of said at least one relay. Always according to the invention, the enabling means may comprise voltage source means controlled by the switching means.

Still according to the invention, the enabling means may comprise the infrared light emitting diode, or LED, of at least one solid state relay, having N contacts and two positions, further comprising at least one infrared photodetector for triggering N TRIAC, the infrared LED being connected to said voltage source means.

Further according to the invention, the sectioning means may comprise at least one infrared photodetector for triggering at least one TRIAC of said solid state relay.

Always according to the invention, the enabling means may be apt to be electrically supplied by the mains through a connector.

Preferably according to the invention, the enabling means and the sectioning means are placed in correspondence with the connector. It is further specific subject matter of this invention an electrical apparatus, apt to be electrically supplied by a mains through at least one power supply cable, characterised in that it comprises switching means apt to control the enabling means of a safety device as just described.

By way of illustration and not by way of limitation, such electrical apparatus may be a hairdryer, an electric shaver, a radio, a thermofan, a heater, or an instrument such as a welding machine, a cutting-off machine, a circular saw, or any high power apparatus. Similarly, boards provided with electrical supply may also be provided with the device according to the invention. It is also specific subject matter of this invention a power supply cable for an electrical apparatus, characterised in that it comprises the enabling means and the sectioning means of a safety device as previously described. Such a cable, coupled to an electrical apparatus as just illustrated, realises the safety device according to the invention. In particular, such a power supply cable comprises, besides the supply wires, also the electrical conductors for connecting the enabling means and the switching means with which the apparatus is provided.

It is also specific subject matter of this invention a power supply cable for an electrical apparatus, characterised in that it further comprises the switching means of a safety device as previously described. Such a cable, also comprising the supply wires, could allow the safety device to be applied to already existing electrical apparatus which are not provided with the switching means of the device: it is sufficient to connect the supply wires of the power supply cable to the power supply of the apparatus and to apply, through a suitable support, the switching means to the same apparatus. The present invention will be now described, by way of illustration and not by way of limitation, according to its preferred embodiments, by particularly referring to the Figures of the enclosed drawings, in which:

Figure 1 shows a diagram of a first embodiment of the safety device according to the invention;

Figure 2 shows a diagram of a second embodiment of the safety device according to the invention; and

Figure 3 shows a diagram of a third embodiment of the safety device according to the invention. In the following of the description same references will be used to indicate alike elements in the Figures.

With reference to Figure 1 , it may be observed that a first embodiment of the safety device according to the invention, applied to an electrical apparatus 1 , comprises a power supply enabling unit 2, controlled by a two-position button 3. The power supply enabling unit 2, supplied through a connector 6 for supplying from the mains 4 which supplies the electrical apparatus 1 as well, controls a sectioning unit 5, comprising one or more switches, having an open configuration and a closed configuration. The sectioning unit 5 is connected between the connector 6 and the electrical apparatus 1 , to which it provides with the power supply from the mains 4 when it is in closed configuration.

In particular, the power supply enabling unit 2 and the sectioning unit 5 are placed in correspondence with the supply connector 6, typically a plug, connectable to a corresponding connector for drawing power supply from the mains, typically a socket. Instead, the button 3 is placed in correspondence with the electrical apparatus 1 , so as to be easily operated by a user.

The two position of the button 3 corresponds to a home configuration, wherein the button 3 is not operated, and to a second enabled configuration, wherein the button 3 is pressed. In the home configuration of the button 3, the power supply enabling unit 2 keeps the sectioning unit 5 in the open configuration, wherein the electrical apparatus 1 does not receive power supply from the mains. Vice versa, in the enabled configuration of the button 3, the power supply enabling unit 2 controls the sectioning unit 5 in order to make it assume the closed configuration, wherein the electrical apparatus 1 receives power supply from the mains. In particular, in rest conditions the sectioning unit 5 is in the open configuration.

In the embodiment of the safety device according to the invention shown in Figure 1 , the same cable comprising the supply wires for the electrical apparatus 1 further comprises two electrical conductors for connecting the button 3 to the enabling unit 2: a first conductor upstream and a second conductor downstream the button 3.

With reference to Figure 2, it may be observed a second preferred embodiment of the safety device according to the invention, which comprises a male connector 6, connectable to a corresponding connector for drawing power supply from the mains 4. The male connector 6 is connected to a enabling unit 2 power supply which comprises a transformer 7, in turn connected to a voltage rectifying circuit 8 and to a capacitor 9, apt to stabilise the oscillating voltage coming from the rectifying circuit 8. The stabilised output of the rectifying circuit 8 delivers power to the further components of the enabling unit 2 which make a current source up. In particular, the current source comprises a resistive divider, made up by two resistors 10 and 11 , for biasing a NPN transistor 12 in common emitter configuration, the base of which is connected to said divider and the emitter of which is connected to circuit ground. A button 3, capable to be operated by a user of the electrical apparatus 1 , is connected between the base of the transistor 12 and circuit ground. The collector of the transistor 12, which is the output of the current source, is connected to the anode of a protection diode 13 and to a terminal of the coil 14 of an two-contact two-position electromechanical relay; the cathode of the diode 13 and the other terminal of the coil 14 are connected to the stabilised output of the rectifying circuit 8. The sectioning unit 5 comprises the two switches 15 and 16 of the electromechanical relay, which are in parallel connection with a corresponding capacitor, respectively 17 and 18, and are therefore connected between the connector 6 and the electrical apparatus 1. In the rest position, wherein the coil 14 is not crossed by any current, the two switches 15 and 16 are in open position and the electrical apparatus is not connected to the connector 6. In the home configuration, the button 3 assumes a closed position wherein the base of the transistor 12 is connected to circuit ground and, therefore, the transistor is off and no current is delivered to the coil 14. Consequently, the switches 15 and 16 are open. When the button 3 is pressed, it assumes an open position, wherein the base of the transistor 12 is connected, through the resistive divider, to the stabilised output of the rectifying circuit 8. The divider biases the transistor 12 to the active region or, more preferably, to the saturation region, and the coil 14 is crossed by a current apt to operate the switches 15 and 16, which consequently close, delivering power to the electrical apparatus 1.

It is still to be noted that the button 3 is placed in correspondence with the electrical apparatus 1 , while all the other components, particularly the relay, are placed in correspondence with the connector 6.

With reference now to Figure 3, a third embodiment of the safety device according to the invention may be observed, wherein the button 3 is in series connection with the branch of the resistor 10. In the home configuration, the button 3 assumes an open position wherein the base of the transistor 12 is connected to circuit ground through the other resistor 11 and, therefore, the transistor is off and no current is delivered to the coil 14. Consequently, the switches 15 and 16 are open.

When the button 3 is pressed, it assumes a closed position, wherein the base of the transistor 12 is connected, through the resistive divider, to the stabilised output of the rectifying circuit 8. The divider biases the transistor 12 to the active region or, more preferably, to the saturation region, and the coil 14 is crossed by a current apt to operate the switches 15 and 16, which consequently close, delivering power to the electrical apparatus 1. In the embodiment shown in Figure 3, in case of accidental cut of the power supply cable, the base of the transistor 12 is again connected to circuit ground and, therefore, the switches 15 and 16 open, turning off the power of the electrical apparatus 1 upstream the power supply cable. The advantages offered by all the embodiments of the safety device according to the invention shown in the Figures are several.

First of all, the electrical apparatus 1 is supplied from the mains only when the user operates the control button 3. In case of accidental fall of the apparatus 1 , the device opens the switches of the sectioning unit 5, turning off the power of the electrical apparatus 1 upstream the power supply cable.

Moreover, even when the connector 6 is inserted, the apparatus 1 is not electrically supplied along the button 3 is operated and, therefore, the electrical risk is null, since the whole power supply cable is not live.

Furthermore, the safety device is simple to be realised and inexpensive.

Still, the safety device according to the present invention may be easily applied to already existing electrical apparatus as well.

The present invention has been described, by way of illustration and not by way of limitation, according to its preferred embodiments, but it should expressly be understood that those skilled in the art can make other variations and/or changes, without so departing from the related scope of protection, as defined by the following claims.

Claims

1. Safety device for at least one electrical apparatus (1 ), apt to be electrically supplied by a mains (4) through at least one power supply cable, comprising sectioning means (5) connected between the mains (4) and said power supply cable, having an open configuration, wherein said power supply cable is not supplied, and a closed configuration, wherein said power supply cable is supplied, the safety device being characterised in that it comprises enabling means (2) controlled by switching means (3) and having a home configuration, wherein the enabling means (2) keeps the sectioning means (5) in the open configuration, and an enabled configuration, wherein the enabling means (2) controls the sectioning means (5) in order to make it assume the closed configuration, the switching means (3) being placed in correspondence with the electrical apparatus (1 ).

2. Device according to claim 1 , characterised in that the switching means comprises at least one button (3), connected through two electrical conductors to the enabling means (2), which is apt to assume alternatively a not operated position, corresponding to the home configuration of the switching means (3), or an operated position, corresponding to the enabled configuration of the switching means (3).

3. Device according to claim 2, characterised in that said two electrical conductors are short-circuited when the button (3) assumes the operated position and are disconnected from one other when the button (3) assumes the not operated position.

4. Device according to any one of the preceding claims, characterised in that the enabling means (2) comprises current source means (10, 11 , 12, 13, 14) controlled by the switching means (3).

5. Device according to claim 4, characterised in that the enabling means (2) comprises the coil (14) of at least one electromechanical relay, having N contacts and two positions, with N ≥ 1, said coil being connected to said current source means (10, 11 , 12, 13, 14).

6. Device according to claim 5, characterised in that the sectioning means (5) comprises one or more switches of said at least one relay.

7. Device according to claim 5 o 6, characterised in that said electromechanical relay is a relay having N= 2 contacts.

8. Device according to any one of the preceding claims, characterised in that the enabling means (2) comprises voltage source means controlled by the switching means (3).

9. Device according to claim 8, characterised in that the enabling means (2) comprises the infrared light emitting diode, or LED, of at least one solid state relay, having N contacts and two positions, further comprising at least one infrared photodetector for triggering N TRIAC, the infrared LED being connected to said voltage source means.

10. Device according to claim 9, characterised in that the sectioning means (5) comprises at least one infrared photodetector for triggering at least one TRIAC of said solid state relay.

11. Device according to any one of the preceding claims, characterised in that the enabling means (2) is apt to be electrically supplied by the mains (4) through a connector (6).

12. Device according to claim 11 , characterised in that the enabling means (2) and the sectioning means (5) are placed in correspondence with the connector (6).

13. Electrical apparatus (1), apt to be electrically supplied by a mains (4) through at least one power supply cable, characterised in that it comprises switching means (3) apt to control the enabling means (2) of a safety device according to any one of the preceding claims 1 to 12.

14. Power supply cable for an electrical apparatus (1 ), characterised in that it comprises the enabling means (2) and the sectioning means (5) of a safety device according to any one of the preceding claims 1 to 12.

15. Power supply cable for an electrical apparatus (1 ), characterised in that it further comprises the switching means (5) of a safety device according to any one of the preceding claims 1 to 12.