Protection against electrical shock

Claim 2

Protective means adapted to reduce the danger of electrical shock in a two-wire non-grounded electrical system, in which current generating means cause a first current to be injected between ground and a first terminal, this current being substantially equal to and in phase with a first leakage current between a first of the two lines of the system and ground, and in which the current generating means cause a second current to be injected between ground and a second terminal, this current being substantially equal to and in phase with a second leakage current between the second of the two lines of the said system and ground, and the said terminals being connected to at least one of the two said lines, whereby the part of the first leakage current which can flow from ground through a body to the second line, and the part of the second leakage current which can flow from ground through a body to the first line, are substantially reduced.

Claim 3

Protective means according to claim 1, and in which the first and second terminals are directly connected together.

Claim 4

Protective means according to claim 1, and in which the first and second terminals are directly connected together and a single current generator serves to produce both the said first current and the said second current.

Claim 5

Protective means according to claim 2, and in which the first and second terminals are both connected to a first only of the two said lines.

Claim 6

Protective means according to any of claims 1, and in which each of the first and second terminals is connected to a tapping on a coil winding connected at its ends respectively to the first and second lines.

Claim 7

Protective means according to claim 2, and in which both the first and second terminals are connected to a center tap on a coil winding connected at its ends respectively to the first and second lines.

Claim 8

Protective means according to claim 2, and in which both the first and second terminals are connected to a center tap on a primary winding of a transformer and the two ends of the said winding are connected respectively to the said first and second lines, and a secondary winding on the transformer provides electrical energy to drive the said cUrrent generating means.

Claim 9

Protective means as claimed in any of claims 1, wherein the system is an alternating current system and the leakage currents include capacitive components.

Claim 10

Protective means as claimed in any of claims 1, wherein the system is an alternating current system, and the protective means include first adjustable means by which compensation for capacitive leakage currents is provided and second adjustable means by which compensation of resistive leakage currents is provided.

Claim 11

Protective means as claimed in any of claims 1, wherein the system includes a plurality of sub-circuits and the protective means include separate adjusting means associated with each of those sub-circuits for compensation of capacitive leakage currents in that circuit.

Claim 12

Protective means as claimed in any of claims 1, and in which the system includes a plurality of sub-circuits and the protective means includes separate adjusting means associated with each of those sub-circuits for compensation of capacitive leakage currents in that sub-circuit, the first and second terminals are directly connected together, and a single generator serves to produce both the said first current and the said second current for all the sub-circuits.

Claim 15

The method according to claim 12, in which both currents are generated in a single current generator.

Claim 16

The method according claim 13, in which the single current generator is connected between ground and one only of the two said lines.

Claim 17

The method according to claim 13, in which the single current generator is connected between ground and a center tap of a coil winding connected at its ends respectively to the two said lines.

Claim 18

The method according to claim 15, in which the said coil winding is a primary winding of a transformer and an alternating current is applied to a primary winding of the said transformer and generates e.m.fs. in two halves of the secondary winding respectively on opposite sides of the center tap.

Claim 19

The method of claim 12, and in which the system is an alternating current system and the leakage currents include capacitive components.

Claim 20

The method of claim 12, and in which separate adjustments of the injected current are carried out to compensate respectively for capacitive and for resistive components of the leakage current.

Claim 21

A protective device suitable for connection to a two-wire non-grounded electrical system and including connections respectively to ground, to a first of two lines of the system, and to a second of the two lines of the system, current generating means arranged to cause a first current to be injected between ground and a first terminal, this current being adjustable to be substantially equal to and in phase with a first leakage current between the said first line and ground, the current generating means also being arranged to cause a second current to be injected between ground and a second terminal, this current being adjustable to be substantially equal to and in phase with a second leakage current between the said second line and ground, and the said terminals being connected to at least one of the two said lines, whereby the part of the first leakage current which can flow from ground through a body to the second line, and the part of the second leakage current which can flow from ground through a body to the first line, are substantially reduced.

Claim 22

A protective device suitable for connection to a two-wire non-grounded electrical system and including connections respectively to ground, to a first of two lines of the system, and to a second of the two lines of the system, current generating means arranged to cause a first current to be injected between ground and a first terminal, this current being adjustable to be substantially equal to and in phase with a first leakage current between the said first line and ground, the current generating means also being arranged to cause a second current to be injected between ground and a second terminal, this current being adjustable to be substantially equal to and in phase with a second leakage current between the said second line and ground, and the said terminals being connected to at least one of the two said lines, whereby the part of the first leakage current which can flow from ground through a body to the second line, and the part of the second leakage current which can flow from ground through a body to the first line, are substantially reduced.

Claim 23

A protective device as claimEd in claim 19, and in which first adjustable means enable the first current to be adjusted to match a capacitive leakage current, second adjustable means enable the first current to be adjusted to match a resistive leakage current, third adjustable means enable the second current to be adjusted to match a capacitive leakage current, and fourth adjustable means enable the second current to be adjusted to match a resistive leakage current.

Claim 24

A protective device as claimed in claim 20, and in which the system to be protected includes a plurality of sub-circuits and the protective means includes separate adjusting means associated with each of those sub-circuits for compensation for leakage currents in that sub-circuit, the said first and second terminals are connected together, and a single generator serves to produce both the said first current and the said second current for all the sub-circuits.