SAFETY SOCKET

Abstract

A safety socket (100) for protecting against a series fault comprises a thermal switch (30; 31) mounted in the socket (100) and configured to interrupt the supply current when a detected temperature exceeds a threshold temperature. The safety socket (100) further comprises an indicator (8; 10; 80) for indicating the socket (100) when the detected temperature exceeds the threshold temperature.

Claims

1-9. (canceled)

10. A safety socket for protecting against a series fault comprising: a thermal switch mounted in the socket and configured to interrupt the supply current when a detected temperature exceeds a threshold temperature; and an indicator for indicating the socket when the detected temperature exceeds the threshold temperature.

11. The safety socket according to claim 10, wherein the thermal switch is normally open and part of a ground fault line such that a ground fault protection interrupts the supply current when the normally open thermal switch closes.

12. The safety socket according to claim 11, wherein the ground fault line comprises a normally closed timer switch.

13. The safety socket according to claim 12, wherein the ground fault line comprises a ground resistor.

14. The safety socket according to claim 13, wherein the normally closed timer switch comprises a safety resistor with a resistance less than the resistance of the ground resistor.

15. The safety socket according to claim 10, wherein the thermal switch is normally closed, and forms part of a phase conductor within the socket.

16. The safety socket according to claim 10, further comprising a residual current device in the socket, wherein the residual current device interrupts the supply current when a ground fault current exceeds its predetermined sensitivity.

17. The safety socket according to claim 10, wherein the thermal switch comprises a meltable element.

18. The safety socket according to claim 10, wherein the socket comprises a child safety mechanism for inhibiting access to a phase through contact holes in the socket.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will be explained with reference to exemplary embodiments and the accompanying drawings, in which

[0026] FIG. 1 illustrates a principle drawing of the invention at prior art,

[0027] FIG. 2 illustrates a principle drawing of the invention with new component,

[0028] FIG. 3 illustrates a back view of a socket,

[0029] FIG. 4 illustrates a contact and indicator activated by a meltable element,

[0030] FIG. 5 is an alternative diagram and

[0031] FIG. 6 illustrates the embodiment in FIG. 5.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0032] The drawings are schematic and not necessarily to scale. For ease of understanding, numerous details known to the skilled person are omitted from the drawings and following description.

[0033] FIG. 2 shows a phase 1 supplying current to a load 10. There are typically several such phases 1 and loads 10 on a branch circuit. The dash dot box 100 illustrates one socket on the branch circuit. The ground resistor 5, ground 7 and ground fault protection 20 are as described above. A normally open thermal switch 30 replaces the heat developing sensor 3 in FIG. 1. More particularly, the thermal switch 30 connects the live connector 1 to ground 7 if the temperature within the socket 100 rises to a level indicating a series fault. However, the thermal switch 30 may be based on any working principle, e.g. using a bimetal junction or another electrically detectable principle to detect temperature.

[0034] A ground fault connection 50 includes the normally open thermal switch 30, a normally closed timer switch 60 and the ground resistor 5, and connects the phase 1 to ground 7 if both switches are closed.

[0035] The timer switch 60 is connected in series with the ground resistor 5, and opens a set time after the thermal switch 30 closes. This interrupts a ground fault current through the ground fault connection 50. This allows the ground resistor 5 to be designed to dissipate the power caused by the ground fault current. For example, a ground resistance of 3 k and a ground current of 30 mA would yield a power of 2.7 W according to equation 1, and the associated heat could conveniently be dissipated through a surface of resistor 5. The timer switch 60 may comprise an electronic circuit. Alternatively, the timer switch 60 may comprise a safety resistor 6 configured to burn off in a controlled manner by the ground fault current. In the latter case, the resistance of safety resistor 6 should be small compared to the resistance of the ground resistor 5, such that the ground resistor 5 determines the ground fault current through the ground fault connection 50 for all practical purposes.

[0036] FIG. 3 shows a socket 100 viewed from behind. The components are mirrored about a diagonal line from the upper left corner to the lower right corner, such that each live connector 1 is connected in the same manner.

[0037] The contact 2, heat development sensor 3, ground resistor 5 and safety resistor 6 are connected as described above. The ground resistor 5 is connected to a ground 7 through a ground contact 51. An indicator 8 will become visible on the front of the socket 100 and indicate the location of the fault when the heat development sensor 3 has altered its state.

[0038] A child safety mechanism prevents inadvertent access to phases behind contact holes in the socket 100. The child safety mechanism comprises a bar 40 that covers the phases in a protecting position. The bar 40 has inclined faces that cause a rotation about a pin 41 when a plug is inserted into the contact holes. A stopper 43 limits the rotation, and a return spring 42 is arranged to rotate the mechanism back to the protecting position when the plug is withdrawn from the socket 100.

[0039] FIG. 4 is a side view illustrating the heat development sensor 3, an open contact 2, 4 and an indicator 8. The heat development sensor 3 will melt or alter its state when the temperature reaches a predetermined level, e.g. 60-70 C. The contact 2 is mounted on a distal end of a spring biased arm, and will descend into contact with the ground contact point 4 when the heat development sensor 3 melts. This establishes contact to ground 7 through ground resistor 5. Similarly, the indicator 8 is mounted on a distal end of a spring biased arm, and will descend into a hole 9 when the heat development sensor 3 melts. The indicator 8 will become visible on the front of the socket 100 and indicate the location of the fault.

[0040] FIG. 5 is a schematic diagram over an alternative embodiment, where an optional residual current device (RCD) 21 and a normally closed thermal switch 31 are mounted within the socket 100. The RCD 21 works in the same way as the ground fault protection 20 described above, and may be implemented by a thyristor. Contrary to the normally open thermal switch 30 described above, the normally closed thermal switch 31 will open at the predefined temperature. By integrating the normally closed thermal switch 31 in the socket 100, the current through load 10 will be interrupted when the thermal switch 31 opens. Any other appliances on the branch circuit will not be affected. Once tripped, the normally closed thermal switch 31 may be latched in the open position. This prevents any further current through the series fault regardless of whether a ground fault protection 20 is installed or not. Similarly, the optional RCD 21 would isolate the load 10 without affecting other appliances on the branch circuit.

[0041] The location of the fault may be detected as the load 10 does not work when plugged into the socket 100 with a series fault. Thus, the load 10 indicates the socket 100 when the detected temperature exceeds the threshold temperature. Alternatively, the location of the fault may be indicated through an electronic signal triggering an indicator 80. The indicator 80 may be part of a central, a signal board or any other means known in the art.

[0042] FIG. 6 illustrates the alternative embodiment of the socket 100 shown in FIG. 5. The ground 7 is illustrated by a rail that can be connected to a ground wire by terminals 12. A phase conductor 14 is connected to a wire 13 through a terminal 12. A contact sleeve 11 is connected to the phase conductor 14. The normally closed thermal switch 31 forms part of the phase conductor 14, and interrupts the current through the phase conductor 14 when it opens. The wire 13 and the phase conductor 14 form parts of the phase 1 when joined at terminals 12. The socket 100 can thus provide current to the load 10 when the plug is inserted into the contact sleeves 11.

[0043] Thus, as the socket 100 is not in use it will be child proof; the circuit will be protected against a serial fault even if a ground fault protection 20 is not working or not installed, and the fault can be located via an indicator 8, 80.

[0044] While the invention has been described by examples, various alternatives and modifications will be apparent to one skilled in the art. The invention is defined by the accompanying claims.