The invention relates to a method for protecting an electrical connector and to an associated device.

The electrical power supply system inside a home or office is exposed to certain dangerous conditions which cannot be detected by ordinary protection systems such as fuses, magneto-thermal switches and/or differential switches..

A condition of this kind occurs when an electrical connector, for example the socket for connection to the mains power supply or the plug connected to a user appliance, has a contact resistance which is too high for the load current, this normally being due to oxidation or loosening of the terminals. Consequently, there is an increase in the temperature of the socket/plug system owing to the Joule effect. The same condition may occur in the case of use of a branched socket (T-union) which is unsuitable or too small for the power to be used.

This situation is potentially very dangerous since it becomes worse over time owing to a positive feedback process: the increase in temperature causes an increase in the contact resistance and therefore an increase in the dissipation due to the Joule effect which in turn causes a further increase in the contact resistance. This may result in charring or melting of the plastic from which the plug and socket are made, with the possibility of a fire starting or in any case the release of toxic fumes into the environment.

The object of the present invention is to provide a system for providing protection against these types of accidents.

This object is achieved by a method for protecting an electrical connector which can be powered by a source and can be connected to a load by means of contacts, characterized in that it comprises the step of detecting the internal temperature of said connector.

The invention also comprises an electrical connector which can be powered by a power supply source and can be connected to a load by means of contacts, characterized in that it comprises a protection device having at least one component sensitive to the internal temperature of the connector.

The electrical connector to which the invention applies may be equally well a male component (for example a plug) or a female component (for example a socket) and therefore when reference is made to only one component it is understood that the other one is not excluded. More generally the invention may be applied to all those types of connectors which have contact terminals.

In an advantageous embodiment of the invention an electromechanical circuit to be inserted inside a connector is used. This electromechanical solution uses the thermally sensitive part of a magneto-thermal switch so that the temperature which causes deformation of a bimetallic strip is the temperature of the metal contacts of the connector.

An automatic switch actuated by a bimetallic temperature sensor or, more advantageously, by an electronic circuit may be inserted inside the connector. This circuit, which may be already present inside the socket for other functions, must be able to

detect the temperature and/or signal danger and/or disconnect the power supply in the event of danger.

It is also possible to use a temperature sensor (for example a thermistor) connected to a circuit which controls a switch in series with the load.

The thermistor should be positioned as close as possible to the contacts of the connector, so as to measure the temperature thereof. It is possible to provide a thermal connection between the two contacts using a steatite strip which has a thermal resistance comparable to that of aluminium (usual metal for contacts) or use two thermistors, one for each contact.

An advantage of the invention is the simplicity with which it may be associated with the already existing active or passive protection system.

A temperature control system for implementing brown-out protection according to the invention may be incorporated very simply into any circuit, especially if the latter comprises a microprocessor. An example is the electronic protection system of the Applicant and described in international patent application No. PCT/IT2004/000222. In this protection system an electronic circuit is already present inside an electrical plug for ensuring protection against dispersion currents and, by merely adding a thermistor and passive components to the circuit and providing suitable control by the microprocessor, it is possible to obtain the brown-out protection according to the present invention.

A variant of the invention includes the use of at least two temperature sensors, one situated on the contacts of the connector and the other at a distance

therefrom and able to detect the temperature of the external environment. By evaluating the difference in temperature between the contacts and the environment it is possible to determine the quantity of heat generated per unit of time as a result of the Joule effect, this being the main source of brown-out danger.

Estimation of the heat generated may be performed by means of a suitable electronic circuit or advantageously by means of a microprocessor (or any equivalent processing unit) . Moreover, by determining (preferably via software) the derivative of the temperature currently present at the contacts and performing a predictive calculation it is possible to activate protection well in advance of the presence of a dangerous temperature at the contacts.

The characteristic features and advantages of the invention will become clear from the following description of an example of embodiment of the invention, shown in the accompanying drawings, in which:

Fig. 1 shows a schematic diagram of the invention;

Fig. 2 shows a schematic diagram of a first variant of the invention;

Fig. 3 shows a schematic diagram of a second variant of the invention.

With reference to Fig. 1, two leads 11a, lib from a power supply source 10 (for example the electricity mains) convey power, downstream of a switch 30, to an electrical socket 20 with contacts 22, 24.

A bimetallic temperature sensor 40 is present in the immediate vicinity of the contacts 22, 24, inside the socket 20. Said sensor 40 is sensitive to the

temperature of the contacts 22, 24 and trips the switch 30 via a control device 50. When the temperature of the contacts 22, 24 exceeds a predefined limit (which in this case may be defined by the properties of the bimetallic strip) , the sensor 40 trips the switch 30 via the control device 50, opening it.

The control device 50 may be, for example, a mechanical actuating system which, following deformation of the sensor 30, releases a retaining pawl inside the switch 30, causing it to open. The switch 30 may also be incorporated directly inside the socket 20.

If we now consider Fig. 2, two leads Ilia, 111b from a power supply source 110 convey power, downstream of a relay 160, to an electrical socket 120 with contacts 122, 124. The relay 160 is excited by a -coil 162 controlled by an electronic circuit 170 which, via a line 172, receives data relating to the temperature of the contacts 122, 124. Said temperature data is supplied by a temperature sensor 180 situated in the immediate vicinity of the contacts 122, 124. When the temperature of the contacts 122, 124 exceeds a predefined limit (which can be defined by a suitable parameter inside the circuit 170) , said circuit 170 trips the relay 160, driving the coil 162, disconnects the socket 120 (and therefore the associated load, not shown) from the power supply 110.

It should be noted that, in Fig. 2, the socket 120, shown in broken lines, comprises the circuit 170. This is because an advantageous embodiment of the invention envisages that the sensor 180 is interrogated by the circuit 170 which is installed inside the socket

120 and is powered directly by the power supply source, via the leads 112a, 112b. In this way the socket 120 and the brown-out protection system according to the invention are inseparable, thereby increasing the safety.

The circuit 170 may be entirely analog or advantageously comprise a microprocessor for acquiring data from the sensor 180 and managing the relay 160. The microprocessor is clearly also able to perform other functions, for example implement other types of active electrical protection. It is possible to provide, on the outside of the socket 120, acoustic and/or luminous signalling devices which are indicated overall by the reference number 200 and are driven by the circuit 170 and have the function of providing the user with a danger signal.

In addition to the thermistor, other sensors, such as thermocouples or diode sensors, may be used. The circuit 170 may also be outside the socket 170, for example inside a centralized control device for a plurality of sockets 120.

The circuit 170 may be conveniently powered also by a battery or by solar cells so that it is independent of any external power supply, while all types of switches, including for example semiconductor switches, may be used instead of the relay 160. Both the relay 160 and the switches may be incorporated directly inside the socket 120.

Another sensor 190, for detecting the temperature of the external environment, may be arranged on the socket 120, far from the contacts 122, 124. By connecting the sensor 190 to the circuit 170, the

latter is thus able to evaluate the difference in temperature between the contacts 122, 124 and the environment in order to determine the quantity of heat generated per unit of time by the Joule effect at the contacts 122, 124.

By obtaining moreover the derivative of the current temperature at the contacts 122, 124 it is possible to activate protection well before the temperature at the contacts 122, 124 becomes dangerous.

A variant of the invention is shown in Fig. 3, where the reference numbers indicate components identical to those shown in Fig. 2. The circuit 170 is now outside the socket 120 and receives temperature data from the sensor 180 via the line 172. In this way it is possible to obtain remote protection for the socket 120 or provide centralized protection for several sockets 120.

It should be noted that, in general, the line 172 may be a cable or any wireless (radio, infrared or other) connection.

These and other variants are contained within the scope of protection of the following claims.