Safety device for detecting ground current and safety electrical plug equipped with said device

Claim 2

Safety device for detecting ground current in coverings and containers of electrical equipment characterized in that it comprises ground current sensing means connected in series with the ground conductor of the equipment and designed to supply a signal proportional to the ground current, first and second threshhold comparator means to whose inputs there is supplied the aforesaid signal proportional to the ground current in the same manner as reference signals supplied by a generator and proportional to a maximum and a minumum ground current value respectively to define a range of variability thereof, an OR port connected to the outputs of the aforesaid first and second theshhold comparator means and whose output is connected to means of signalling and/or activating protection devices.

Claim 3

Device in accordance with claim 1 characterized in that it provides further means of memorization of the signal proportional to the ground current to supply a reference signal to third threshhold comparator means to whose other input is sent the instantaneous value of the signal proportional to the ground current, means of gating of memorization operating on said memorization means, means of visual and/or acoustic signalling which supply a response to the output signal of said third threshhold comparator means.

Claim 4

Device in accordance with claim 2 characterized in that the memorization means comprise analog-digital converter means for memorizing in numerical form a voltage value representing said signal proportional to the ground current and analog-digital converter means connected to the output of the aforesaid analog-digital means and with their output connected to the input of the third threshhold comparator means to supply said reference signal.

Claim 5

Device in accordance with claim 2 characterized in that the memorization gate means operate on the memorization means periodically at preset intervals.

Claim 6

Device in accordance with claims 1 and 2 characterized in that the aforesaid ground current sensing means are made up of a resistor connected in series with the ground conductor of the electrical equipment.

Claim 7

Device in accordance with claims 1 and 2 characterized in that a condenser is connected between the conductor of one of the phases of the supply current and the ground conductor of the electrical equipment to derive from the former a current which flows into the latter to obtain a detectable level of ground current.

Claim 8

Device in accordance with claim 6 characterized in that the condenser has a value between a few tens and a few hundred nanofarad.

Claim 9

Electrical safety plug comprising three contact conductors for connection to the two phases and ground respectively of an electrical system and a body supporting said conductors characterized in that it comprises a ground current sensor connected in series with the central ground conductor and a condenser connected in parallel between the ground conductor and one of the other two conductors, a body with an open boxlike form arranged in such a manner as to surround the three conductors of the plug and having three through holes corresponding to the ends of the three conductors, the sides of this second body being able to slide in a corresponding longitudinal cavity provided peripherally and internally to the supporting body, elastic pressure means connecting the two bodies in such a manner that, due to the effect of their compression, the three conductors integral with the supporting body pass through the holes in the boxlike body and are ready to be inserted in an electrical power outlet, locking means provided laterally and externally to the second body and which are associate with means of control of their axial movement in such a manner as to engage operationally with a corresponding cavity in the supporting body of the conductors when said elastic means are compressed and disengage from said cavity in response to an electrical signal supplied to said control means and indicating an anomaly in the ground current flowing in the central conductor.

Claim 10

Electrical safety plug comprising three contact conductors for connection to the two phases and ground respectively of an electrical system and a body supporting said conductors characterized in that it comprises a ground current sensor connected in series with the central ground conductor and a condenser connected in parallel between the ground conductor and one of the other two conductors, a body with an open boxlike form arranged in such a manner as to surround the three conductors of the plug and having three through holes corresponding to the ends of the three conductors, the sides of this second body being able to slide in a corresponding longitudinal cavity provided peripherally and internally to the supporting body, elastic pressure means connecting the two bodies in such a manner that, due to the effect of their compression, the three conductors integral with the supporting body pass through the holes in the boxlike body and are ready to be inserted in an electrical power outlet, locking means provided laterally and externally to the second body and which are associate with means of control of their axial movement in such a manner as to engage operationally with a corresponding cavity in the supporting body of the conductors when said elastic means are compressed and disengage from said cavity in response to an electrical signal supplied to said control means and indicating an anomaly in the ground current flowing in the central conductor.

Claim 11

Electrical safety plug in accordance with claim 8 characterized in that said elastic pressure means consist of a helical spring wound around the central ground conductor and whose ends engage in corresponding projections of the two bodies of the electrical plug.

Claim 12

Electrical safety plug in accordance with claim 8 characterized in that said locking means comprise a retainer integral with a core of magnetic material which slides under the effect of a pressure spring between the turns of an electromagnetic coil whose excitation circuit constitutes said control means supplied with the signal indicating an anomaly in the ground current.

Claim 13

Electrical safety plug in accordance with claims 8 and 10 characterized in that said retainer consists of a pin with a beveled face which in the compression movement of the aforesaid elastic means connecting the two bodies of the plug engages against a fin with mirror image bevelling of the body supporting the plug conductors and penetrates thereafter the aforesaid cavity of said body.

Claim 14

Electrical safety plug in accordance with claims 8 and 11 characterized in that it is equipped with the safety device in accordance with claims 1 to 7.

Claim 15

Electrical safety plug in accordance with claims 8, 10 and 12 characterized in that the excitation circuit of the coil of the locking means is connected to the output of the OR port of the safety device to detect the ground current in accordance with claims 1 to 7.