WO1987000977A1

WO1987000977A1 - Improvements in electrical plugs

Info

Publication number: WO1987000977A1
Application number: PCT/GB1986/000475
Authority: WO
Inventors: Hugh Heathcote Gilbert
Original assignee: Hugh Heathcote Gilbert
Priority date: 1985-08-09
Filing date: 1986-08-06
Publication date: 1987-02-12
Also published as: GB8800665D0; GB2198598A; HK86693A; GB2198598B; AU6192086A

Abstract

The insulating body of an electrical plug has a lid (1) turnably mounted on a plug base (2) for movement between open and closed positions. The plug pins (4) include a terminal end (5) protected within the body which defines a wire trap with a second terminal end (6) movable with the lid (1). The body exhibits passage means (7) for each wire leading to the respective terminal end, each passage means (7) being adapted to receive wire only when fed in endwise, the lid (1) being mounted on the plug base (2) for turning movements about an axis (x) parallel to the axes of the pins (4), whereby on endwise insertion of wires into the respective passages (7) with the lid (1) in the open position, the end of each wire is located between the terminal ends (5, 6) of the respective wire trap, and the wire traps close around the wires as the lid is moved into its closed position to effect wiring up of the plug.

Description

Improvements in electrical plugs

Technical Field

This invention relates to improvements in re irable electrical plugs.

Background of the Invention

Electrical plugs are well known devices required to connect the supply lead of an electrical appliance to mains electric wiring via a socket. There are a var¬ iety of amperage ratings for electrical plugs and they range from devices employing two contact pins to devices having three contact pins and occasionally more.

The wiring-up of a conventional electrical plug is achieved by removing a covering lid forming part of the electrically insulating body of the plug, revealing the terminals of the contact pins, inserting the appropr¬ iate wires of the supply lead into the appropriate ter¬ minals, fastening the wire ends in place by screw or other means, and securing the supply lead to the body of the plug at the point of entry of the supply lead to the plug body.

There is included in the body- of some designs of conventional electrical plugs, particularly the 3-pin, 13 Amp rated plugs, a fuse of rated current capacity.. Such a fuse occasionally blows or fails through age or requires replacing for some other reason.

Conventional electrical plugs are however, very awkward to wire-up due to their small size and the wiring- up operation can be a time-consuming and laborious busi¬ ness, during which the wires may be damaged or the termin¬ als incorrectly tightened onto the wire ends. These plugs are intended for anyone to be able to wire, however, it can be dangerous for the inexperienced and aged. Furthermore, the process of wiring-up a plug involves the exposure of metal that can be at mains voltage while exposed. It is quite possible to insert many -existing designs of rewirable electrical plugs, with the lid off, into the socket they are to be used with, (e.g. by apply- ing slight finger pressure on the earth terminal). It is easier still to leave out the cover lid securing screw in many designs of plugs, hold the lid in place, insert the plug into the socket and then remove the lid or allow it to drop off, exposing one terminal at mains voltage.

Discussion of Prior Art

Various proposals have been made to simplify the wiring-up of electrical plugs. In GB-B-1600066 grooves are provided from a supply lead entry port to terminal members of a plug having a two-part body, wiring-up involving laying the wires in the grooves and trapping them there -by hinging the two parts of the plug body together. GB-A-2047989 discloses a plug in which the wires are manually laid from a lead entry port to the ends of the plug pins, the wire ends being clamped into contact with the plug pins using separate wire gripping members compressed by coaction between two separable parts of the plug body housing.

GB-A-2026784 also shows a hinged two-part body, the closing of the body trapping wires, manually laid in place on one part of the body, in contact with termin¬ als of the plug pins.

However, operating these known arrangements can require as much dexterity as with a conventional screw- connected arrangement and the major hurdle of feeding the wires to the individual terminals has not been over¬ come. It is also extremely easy to leave two parts of the plug body insecurely fixed together, so that follow¬ ing insertion of the plug in a socket, a terminal at mains voltage can be exposed.

The process of replacing a fuse may be more fre¬ quently required and is equally time consuming. It often requires removing the cover lid of the plug and exposing the terminals, and can require the application of -con¬ siderable force and a fair degree of manual dexterity to replace the fuse.

There are designs of plug that permit fuse replace¬ ment without the necessity of removing the cover lid from the plug body, however, these plug designs still require the use of considerable force and a great deal of manual dexterity to effect a fuse replacement.

It is necessary to gauge the length of wires required within the plug body, before wiring-up and there is rarely if ever, a gauge provided to assist in doing this.

Furthermore, the length of each wire is often different to its accompanying wires in the supply lead.

Failure to get the correct lengths of wire results in either not gripping the outer sleeve of the supply lead with the cord entry grip provided in the plug body, because too long lengths of wire have been exposed or straining the terminal connections- because too short lengths have been left exposed.

This invention seeks to provide an improved design of electrical plug in which some of the shortcomings of existing plug designs are avoided.

Statement of Invention

In its broadest aspect, an electrical plug according to this invention comprises an electrically insulating body comprising a lid turnably mounted on a plug base for movement between open and closed positions relative to the plug base, the plug base having at least two plug pins passing therethrough which pins have parallel axes and are exposed on that side of the plug base remote from the lid, each pin including a terminal end protected within the body which terminal end defines a wire trap with a second terminal end movable with the lid, the body exhibiting an opening through which a pluri-wire supply lead can pass into the body and passage means for each wire leading from the opening to the respective terminal end to permit electrical connection to be made between respective wires of the lead and the terminal ends in the plug body, characterised in that each passage means is adapted to receive wire only when fed in endwise from the opening and in that the lid is mounted on the plug base for turning movements about an axis parallel to the axes of the pins, whereby on endwise insertion of wires into the respective passages with the lid in the open position the end of each wire is located between the terminal ends of the respective wire trap, which wire traps close around the wires as the lid is moved into its closed position.

Conveniently, the lid is captively mounted on the plug base so that although free to -move between the open and closed positions, once fitted on the plug base, the lid cannot be removed from the plug base without damaging the plug body. This facility ensures it is impossible to expose the terminals within the plug body, even with the lid in the open position.

Suitably at least one terminal end that moves with the lid is designed to surround the other terminal end of the respective wire trap in the closed condition of the wire traps.

Desirably, each wire end is bent through approxi¬ mately a right angle between the end of the passage means closest to the respective second terminal end and its position in the closed wire trap. Each second terminal end can form a U-shaped member into which the respective terminal end connected to a pin enters in the closed condition of the respective wire trap.

The ends of the wires are stripped of insulation before the wires are fed into the respective passage means and the plug body can include means to gauge the length of each wire required for correct wiring-up of the plug and further means to strip the required length of insulation from the free end of each wire.

The supply lead opening of the plug body would nor¬ mally incorporate a grip means (or cord grip) for anchor¬ ing the lead in the opening, such a grip means can be moved between gripping and non-gripping positions as the lid is turned between its open and closed positions.

Where the plug body incorporates a fuse, a passage can be provided in the body into which a cartridge fuse can be located when the lid is in the closed position and which fuse serves to complete the electrical connec¬ tion between one terminal end and its associated pin and also serves to lock the lid in its closed position. Suitably, the cartridge fuse is mounted in a carrier that is insertable into the passage provided therefor in a direction normal to the axis about which the lid turns on the base. As an alternative, however, the car¬ tridge fuse is mounted in a carrier that is insertable into the passage provided therefor in a direction parallel to the axis about which the lid turns on the base. The passage provided for the cartridge fuse (or its carrier) can afford access to the supply lead opening when the lid is in its open position.

The passage means for each wire are desirably all of substantially the same length from the opening to the respective second terminal end, so that each wire of the supply lead can be of the same length. Since the wires are passed endwise through the respective pass¬ age means (i.e. by means of longitudinal pressure applied from outside the plug body), each passage means is conven- iently smooth bored and the curves therein are of as large a radius of curvature as possible.

Part of the plug body can be made to be transparent to provide visual confirmation that the wires once inserted, are in the correct terminal-connecting posi- tions. Conveniently this is the plug base so that viewing access for the live and neutral terminals is only avail¬ able through that surface of the plug^' which confronts the socket when the plug is inserted therein. However, a viewing window for the earth terminal can be provided in the lid, thus indicating, even during use of the plug, whether the plug has been correctly wired with an earth wire.

The plug may incorporate catch means that retain the lid in the open and/or the closed position.

Brief Description of the Drawings Two embodiments of plug in accordance with the inven¬ tion will now be described, by way of example, with refer¬ ence to the accompanying drawings, in which:-

Figure 1 is a plan of the underside of an assembled first embodiment of plug in the closed position,

Figure 2 is a section on the line II-II of Figure 1,

Figure 3 is a plan of the underside of the assembled plug of Figure 1 in the open position,

Figure 4 is a longitudinal view in elevation of the plug of Figure 1, Figure 5 is a sectional view of the underside of the assembled lid of the plug taken on the line. V-V of Figure 2,

Figure 6 is a sectional longitudinal view of the plug taken on the line VI-VI of Figure 1,

Figure 7 is a plan of the top of the assembled base of the plug of Figure 1,

Figure 8 is a plan of the top of the plug of Figure 1,

Figure 9 is a plan of the underside of the inner lid moulding,

Figure 10 is an axonometric view of the plug in the closed position,

Figure 11 is a cutaway axonometric view of the under- side of the unassembled lid of the plug of Figure 1,

Figure 12 is an axonometric view of the underside of the inner lid moulding,

Figure 13 is an axonometric view of the assembled base of the plug of Figure 1,

Figure 14 is an axonometric view of the fuse car¬ tridge and fuse assembled therein,

Figure 15 is a lateral view in elevation of a second embodiment of plug shown in the open position and showing the cord grip,

Figures 16 and 17 are detailed plan views of a wire in the U-shaped cord grip shown in Figure 15, con- taining, respectively, a thin wire and a thick wire,

Figure 18 is a lateral view in elevation of the plug of Figure 15 in the closed position

Figure 19 is a plan of the underside of the assembled second embodiment of plug in the closed position, and

Figure 20 is a plan of the underside of the assembled second embodiment of plug in the open position.

Description of Preferred Embodiments

The first embodiment of plug is clearly illustrated in the accompanying Figures 1 to 14 and its construction will be appreciated from a study of those Figures in connection with the following description.

The plug shown is a 3-pin fused plug (substantially according to BS 1363:1984) as used in the U.K., one pin

4 (the larger) being the earth pin (E), the left-hand shorter pin 4 in Figure 1 being the live pin (L) and the right-hand shorter pin 4 being the neutral pin (N).

A moulded lid 1 ( in this case opaque ) snaps onto a base 2 ( in this case transparent ) and is retained in position by a groove 13 in the base 2. The lid is capable of twisting through 90°, in relation to the base 2 from an open to a closed position and vice versa.

The base 2 incorporates a slot 10 in which, when in the closed position, a fuse, mounted in a cartridge 11, is slotted (in this case slid in from the_^side, but it could be pushed up from below). This insertion of the fuse completes the electrical connection between the live pin 4 and its wire trap and locks the lid to the base, thereby completing the closing of the plug body (1, 2). Only when the fuse is inserted, i.e. when the plug is closed can the plug be made live. Removal of the fuse prevents any electrical current ^" flowing through a pluri-wire supply lead S to an attached appli¬ ance (not shown).Thus though the plug may be inserted into a socket in the open position it will be totally inoper¬ able and consequently totally safe. If the plug is inserted in the closed position without the locking fuse in position it will still be totally inoperable.

The only way to cause current to flow from the pins 4 to the lead S is to lock the lid 1 in the closed posi¬ tion on the base 2 by insertion of the fuse.

If the fuse cartridge 11 is removed and the lid is twisted to the open position, then the slot 10 in the base coincides with a cord grip 12 and a cord entry passage in the lid 1, allowing the power lead S to be moved up through the base slot 10. To wire up the plug, it is turned to the open position (see Figure 3), and the respective wires of the lead S are cut to a gauged length and bared. The individual filaments of each wire can then be twisted together. Each thus-prepared wire is then pushed endwise through inlet ports 8 in the under¬ side of the lid 1 and along respective wire guides 7. The wire guides 7 can narrow at their downstream ends to prevent insulation penetrating further and thus only allow the bared ends of the wires to enter a respective wire receptor 6.

Each receptor 6 forms a second terminal end of a two part wire trap. When the plug body is closed, a respective terminal end in the form of a probe 5 attached to each pin is forced into the appropriate receptor jamm¬ ing the wire in place in the wire trap. The coaction between a convex probe 5 and a concave receptor 6 has been found to provide a surprisingly simple and reliable way of mechanically locking a wire end to a pin and of effecting a good high-current carrying electrical connec¬ tion. Both probe 5 and receptor 6 used with each pin 4 can be of electrically conducting material (e.g. brass or copper) but either or both could be of non-electrically conducting material, provided some means is provided to secure an adequate low resistance current-carrying electrical connection between each wire and its associ¬ ated pin 4. In the embodiment illustrated in Figures 1 to 14, each wire is retained in position by the probe 5 springing into the crooked shape of the receptor (see Figure 1 ) . Large areas of bared wire are thus forced against the receptor 6 in a shear action and effective electrical contact to the pins 4 is achieved. Preferably contact pressure is maintained by a spring action of the probe 5 snapping into the receptor 6.

In the embodiment illustrated in Figures 1 to 14 , the wire guides 7 are formed by semicircular channels in the lid 1 (Figure 11) coinciding with semicircular channels in an inner lid 3 (made of transparent material in . this case) (Figure 12). This inner lid 3 is welded, glued or otherwise fixed relative to the lid 1. The wire guides 7 may include enlargements to provide excess capacity for taking up extra length in the wires.

The receptors 6 (e.g. of copper) are pushed into the lid 1 and retained in place (e.g. by the provision of one or more dimples - see Figure 5 ) . The cord grip 12 is a flexible member (made from a material such as nylon) which exerts pressure when forced back. The cord entry is shaped so as to guide the cord onto the cord grip.

The fuse cartridge 11 is designed to be snapped into place, and is removable by finger pressure from below so that it can only be removed if the plug is removed from a socket. The plug body may include some form of catch to retain the lid lightly in the open position.

A gauge could be included on the plug body or fuse cartridge for gauging the lengths of wire required. A wire trimmer, gauged for length, could also be included on the plug body.

To replace the fuse:

The fuse cartridge 11 is slid out in a direction parallel to the engagement face of the plug. The fuse (F in Figure 2) is removed from the cartridge, replaced and the cartridge reinserted.

Coded coloured fuse cartridges 11 could be marketed such that all that is required is replacement of a used cartridge by a correctly colour-coded new one.

To wire-up the plug:

The fuse cartridge 11 is removed as described above, looking at the plug from below, pins 4 uppermost, the lid 1 is twisted clockwise relative to the base 2 and the lead S is pulled up through the base slot 10.

The wires of the lead S are cut to the correct gauged length, bared and twisted. Each is then inserted endwise into its respectively marked wire inlet port 8 and pushed along the wire guides 7 into the respective receptor 6. The lead S is then pushed down through the narrowed cord entry into the cord grip 12 and the lid 1 is twisted anticlockwise relative to the base 2 into the closed position.

Electrical contact is completed at each terminal by the probes 5 being, forced into the receptors 6 and this also snaps the lid closed to the base.

The fuse cartridge 11 is then inserted, locking the lid and base together and^~ completing the electrical circuit to the live pin.

The use of convex probes and concave receptors with the wire located in or across the receptor (which could be non-conducting) ensures good electrical connection of the wire with the probe when the lid is turned into its closed position. There is a mechanical advantage achieved in the nesting together of probes and receptors due to the turning axis of the lid being inwardly of both probe and receptor, although parallel to the axes of the parallel pins 4.

The wire traps illustrated can be designed to accommo¬ date conductors of cross-sectional areas ranging from

The lid and - plug base can be separately moulded and after insertion of the plug pins, and any other com- ponents housed within the plug body, the plug body can be completed by snapping the lid into place on the plug base. The engagement between lid and base can be such that after fitting in place, the lid is not disengageable from the base without damaging the plug body, but it is not ruled out that the plug body design should allow lid removal on the application of exceptional force and/or the use of an obscure release procedure. It is also within the scope of this invention to secure the lid to the plug base by a central stud, rtύt or screw mounted on the base rather than by means of the snap-in engage¬ ment of a part of the lid in the groove 13.

The second embodiment of plug shown in Figures 15 to 20 has many features in common with those described with reference to Figures 1 to 14 and only the major differences will here be discussed.

A, The wire traps are shaped differently. The receptor 6 has its leg closest to the turning axis of the lid elongated so that the full length of the bared wire which is allowed to project from the end of the wire guide 7, can be laid along its length and forced into contact by the probe 5, without any wire returning along the bottom of the receptor 6.

This has a number of advantages:

a) The area of contact is greatly increased in the position of greatest pressure, i.e. the wire is in shear over its entire length.

^'b) There is no tendency for bunched wires, for instance, to cause wire in ^' one wire trap to 'bottom out' before any other thus preventing other wire traps closing fully .

c) Soldered wires or solid wires can be used as they do not need to be bent (through approximately a right angle) more than once.

d) There is a greatly increased tolerance for small withdrawal movements of the probe 5 from the receptor 6 without affecting electrical contact pressure due to the greater length of wire in shear contact.

B, The short leg of the receptor 6 of each wire trap is substantially shorter than the long leg. This allows the wire, which initially lies across the receptor to be pushed into the receptor by the probe 5 without snagg¬ ing on the short leg. C. The probe 5 and the receptor 6 of each wire trap are both slightly curved to match the arc on which the probe turns in closing the wire trap. This enhances the snapping together action when the parts of the wire trap are forced together and requires increased pressure to reopen the closed wire trap.

D. The short leg of each receptor 6 retains its respec¬ tive probe 5 in place by means of a bent catch.

E. Modifying the components of each wire trap as described above has allowed them to become slimmer and thus the arc of movement of the probe 5 of the wire trap for the earth pin has been located inside the arc of movement of the probes of the wire traps of the live and neutral pins.

This has a number of advantages.

a) The three channels in which the probes move are now totally separate and permanently insulated from one another. Thus there is no chance of a stray wire from one wire trap contacting another.

b) The probe 5 of the earth pin will have a slightly greater pressure exerted on it, due to its proximity to the centre of rotation, thus this wire will be assured of the most favourable contact.

c) The probe of the earth pin will meet the receptor of the earth pin slightly earlier than the other two probes will meet their respective receptors, due to the decreased circumference of travel, Likewise the probe of the earth pin will leave its receptor last upon moving the lid to its open position.

This means that the earth wire will be in contact before and after the live and neutral wires have made contact.

F. The cord grip has been changed so that when the wires have been fed into their respective guides 7 the lead S is forced down into a U- or V-shaped grip 14 by the user. Final clamping of the wire is achieved by a ramp 15 which forces the lead S further into the grip on rotation of the lid into its closed position. This ramp may be 'knife' -edged so as to cut slightly into the sheathing of the lead S to ensure a better grip.

G. The position of the fuse cartridge has been twisted round by 45° with relation to the cord entry.

This has the following advantages:

1) Greater visual access is given to the inlet parts 8 of the wire guide passages -7 and greater physical access is also allowed.

2) This enables the fuse to be snapped into fuse clips which partly surround the barrel.

Should the fuse be inserted into its clips without the fuse carrier, the lid is still locked to the base by a pin which projects (not shown) from the lid tight up again the barrel of the fuse (in the closed position) which prevents the lid being rotated into the open posi¬ tion relative to the base.

The use of such a pin can also prevent insertion of the fuse if the lid is not fully in the closed position.

H. The fuse carrier is removable only by pulling it up and out from the base, thus it is impossible to remove it when the plug is in a live socket . I. There is no large opening in the wall of the lid as in the first embodiment of plug to allow the fuse to slide out. Thus there is no access at any time for a probe or a finger.

J, The fuse carrier is shown joined to the base by a strong flexible tag 18 made of an electrically insulat¬ ing material such as polypropylene.

This tag 18 is of such a length as to allow easy removal of the fuse carrier but is short enough to prevent the loose fuse carrier from moving outside the circumfer¬ ence of the plug. In this way, the loose fuse carrier can act as a stop member to prevent insertion of the plug into a live socket.

K. The second embodiment of plug incorporates a wire stripper such that a wire is inserted into a gauged length hole 20 in the lid. When the lid is turned on the plug base, a blade 19 mounted on the base passes this hole and cuts the surrounding insulation. The wire is then pulled out and the desired length of insulation is stripped off it.

L. The channels moulded into the lid are U-shaped not semicircular so that the lid insert is flat.

Although the plugs illustrated are 3-pin fused plugs as used in the U.K., it will be apparent that the scope of the invention covers any 3-pin plug or any 2-pin plug in use throughout the world, allowing for specific appli¬ cations in each case.

Although the base and inner lid of both embodiments are shown made from a transparent material they could be made from an opaque plastics material, although viewing windows would then be desirable to ensure proper actuation of the wire traps.

The fuse F can be omitted or replaced by a circuit breaker trip unit.

The pins 4 can be hollow having been made from folded sheet metal (e.g. brass) and such a construction allows the associated probe 5 to be formed integrally therewith in the case of the earth and neutral pins and the assoc¬ iated fuse end contact to be formed integrally therewith in the case of the live pin.

Where the base is made from opaque material, aper¬ tures can be provided in the base 2 aligned with the locations of the probes 5 for the live and neutral pins. These apertures define windows which permit visual inspec¬ tion of at least part of the closed wire traps when, but only when the plug is not inserted in a socket. An aperture (e.g. as shown dotted at W in Figure 8) can also be provided in the lid 1 aligned with the receptor 6 of the earth pin to permit visual inspection of the earth wire trap.

It will be noted that the turning axis of the lid on the plug base (i.e. the point X in Figure 8) is arranged so that it is on the same side of each receptor 6 as the passage through which the wire is fed to it.

This has two particular advantages: a) It allows a smooth sliding action of each probe 5 into its respective receptor 6, and b) makes it most unlikely that the wire will snag as it comes into contact with the probe.

Claims

1. An electrical plug comprising an electrically insulating body comprising a lid turnably mounted on a plug base for movement between open and closed positions relative to the plug base, the plug base having at least two plug pins passing therethrough which pins have parallel axes and are exposed on that side of the plug base remote from the lid, each pin including a terminal end protected within the body, which terminal end defines a wire trap with a second terminal end movable with the lid, the body exhibiting an opening through which a pluri- wire supply lead can pass into the body and passage means for each wire leading from the opening to the respective terminal end to permit electrical connection to be made between respective wires of the lead and the terminal ends in the plug body, characterised in that each passage means is adapted to receive wire only when fed in endwise from the opening and in that the lid is mounted on the plug base for turning movements about an axis parallel to the axes of the pins, whereby on endwise insertion of wires into the respective passages with the lid in the open position, the end of each wire is located between the terminal ends of the respective wire trap, which wire traps close around the wires as the lid is moved into its closed position.

2. A plug as claimed in claim 1, in which the lid is captively mounted on the plug base so that although free to move between the open and closed positions, it cannot be removed from the plug base without damaging the plug body.

3. A plug as claimed in claim 1, in which the pass¬ age means are formed, at least in part, in the underside of the lid.

4. A plug as claimed in claim 1, in which at least one terminal end that moves with the lid is designed to surround the other terminal end of the respective wire trap in the closed condition of the wire traps.

5. A plug as claimed in claim 4, in which _ each wire end is bent through approximately a right angle between the end of the passage means closest to the respec¬ tive second terminal end and its position in the closed wire trap.

6. A plug as claimed in claim 4, in which each second terminal end forms a U-shaped member into which the respective terminal end connected to a pin enters in the closed condition of the respective wire trap.

7. A plug as claimed in claim 1, in which the plug body includes means to gauge the length of each wire required for correct wiring-up of the plug.

8. A plug as claimed in claim 7, in which the plug body is provided with further means to strip the required length of insulation from the free end of each wire.

9. A plug as claimed in claim 1, in which the plug body thereof incorporates a fuse, a passage being provided in the body into which a cartridge fuse can be located when the lid is in the closed position and which serves to complete electrical connection between one terminal end and its associated pin and also serves to lock the lid in its closed position.

10. A plug as claimed in claim 9, in which the cartridge fuse is mounted in a carrier that is insertable into the passage provided therefor in a direction normal to the axis about which the lid turns on the base.

11. A plug as claimed in claim 9, in which the cartridge fuse is mounted in a carrier that is insert¬ able into the passage provided therefor in a direction parallel to the axis about which the lid turns on the base.

12. A plug as claimed in claim 9, in which the passage provided for the fuse affords access to the supply lead opening when the lid is in its open position.

13. A plug as claimed in claim 1, in which the passage means for each wire are all of substantially the same length from the supply lead opening to the respective second terminal end so that each wire of the supply lead can be of the same length.

14. A plug as claimed in claim 1, in which the body of the plug includes means to allow visual confirma- tion that at least one of the wires is correctly located in its wire trap.