GB2028016A - Electric plugs - Google Patents

Abstract

An electric plug 10 comprises a cable clamp which includes a wedge member 22 having a row 23 of serrations which engage complementary serrations in a row 20 on one side of an aperture 18. The opposite side of aperture 18 also carries a row 21 of serrations, and the aforesaid sides of the aperture 18 are convergent in a direction outwardly of the plug. The wedge member 22 has a further row 24 of serrations which co-operate with those in the row 21 to grip the cable 19. Internal partitions 41, 42, 43 in the base 10 overlap partitions in the cover to define separate compartments for respective terminals 15, 17, 35, the overlap of the partitions being maintained even when the base and cover are not fully interengaged. <IMAGE>

Description

SPECIFICATION Electric plugs This invention relates to electric plugs.

In electric plugs it is required to provide a clamp for a cable to which the plug is, in use, connected, so that the tension in the cable is not transferred to terminals on the plug. Such a clamp must be adjustable to accommodate cables of widely varying diameters, without risk of damage to the cable, and preferably also should be such that this adjustment can be effected without the use of tools.

It is one object of the invention to provide an electric plug having a cable clamp which meets the foregoing requirements.

Electric plugs commonly include a separable base and cover which are secured together when the plug is assembled. It is desirable that, in the event that the base and cover become partly separated, it will not readily be possible to pass a wire, or similar instrument, into the plug so as to make contact with the terminals therein, and in particular that it shall not be possible to make such contact by means of a wire passed through an opening the plug which is, in part, occupied by a cable.

It is additionaliy an object of the invention to provide a plug in which the foregoing desideratum is met.

According to one aspect of the invention an electric plug includes an insulating base having an aperture through which a cable can pass, and means within said aperture for clamping the cable to said base, said clamping means comprising a first row of serrations on a first side of said aperture, said first side of said aperture and an opposed second side thereof being convergent in a direction outwardly of said aperture, and a wedge member having a second row of serrations complementary to the serrations in said first row, said wedge member having a face which is opposed to said second side of the aperture when said first and second rows of serrations are interengaged, said cable lying, in use, between said face of the wedge member and said second side of the aperture.

According to another aspect of the invention an electric plug includes a separable insulating base and an insulating cover for said base, and means clamping said base and said cover together, said base and cover being provided with internal partitions which overlap when said base and cover are clamped together.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is an elevation of an electrical plug, Figure 2 is a view on arrow 2 in Figure 1 with a cover of the plug removed, Figure 3 is a section of the assembled plug, on line 3-3 in Figure 2, Figure 4 is a section of the assembled plug, on line 4-4 in Figure 2, Figure 5 shows, to an enlarged scale the base moulding of the plug, seen in the direction of arrow 2, and Figure 6 shows, to an enlarged scale, the moulding of the plug cover, seen in the direction of arrow 6 in Figure 1.

An electric plug has a base 10 and a cover 11 which can be brought into clamping engagement with the base 10 by means of a screw 12. The base 10 and cover 11 are moulded from fire-resistant nylon.

Respective neutral and line pins 13,14 pass through rectangular holes in the base 10. The pin 13 has a shoulder portion 15 of increased rectangular section which serves to locate the pin 13 axially with respect to the base 10. An earth pin 16 is also of rectangular section and passes through a rectangular hole in the base 10. The pin 16 has a shoulder portion 17 of enlarged rectangular section which locates the pin 16 axially with respect to the base 10. The shoulder portions 15, 17 of the respective neutral and earth pins 13,16 have through holes which provide terminal connections for appropriate conductors of a cable, indicated at 19 in Figure 2, and are also provided with clamping screws for securing these conductors in a known manner.The upper end of the line pin 14, has a small length of reduced section which is peened over as shown at 30 in Figure 4, to secure the pin 14to a clip 31 for one end of a fuse 32.

The other end of the fuse 32 is held by a further clip 33 which is secured to a contact strip 34. The contact strip 34 is in turn secured to a terminal block 35 for the line conductor of the cable 19, the block 35 being provided with a clamp screw. The strip 34 has a hole which is a press fit onto an integral projection 36 in the base 10 (see also figure 5).

An aperture 18 in the side of the plug is defined, in part, by respective cut-away portions 18a, 18b in the base 10 and cover 11. The aperture 18 admits the cable 19 so that the conductors thereof may be secured to respective terminals, in the plug. A cable clamp arrangement is provided to prevent any tension in the cable 19 from being transmitted to the terminals. This clamp arrangement comprises a first row 20 of serrations in a wall of the base 10 which also forms a wall of the aperture 18. An opposing wall of the aperture 18 is also provided with a row 21 of serrations, the individual serrations of the row 21 being somewhat sharper than those of the row 20.

The wall which carries the row 21 of serrations is generally parallel to the axis of the cable 19 within the aperture 18, the row 20 is inclined to this axis, so that the rows 20, 21 are convergent in a direction outwardly of the aperture 18.

A wedge member has a face carrying a row 23 of serrations which are complementary to the serrations in the row 21. Another face of the wedge member 22 is provided with a row 24 of serrations which are similar to the serrations in the row 21, the arrangement being such that when the serrations in the rows 20, 23 are engaged each of the rows 20, 21 lies in a plane substantially parallel to the axis of that portion of the cable 19 within the aperture 18. In a preferred embodiment and as indicated in Figure 1, the plane of the row 24 is inclined to the direction of downward movement of the member 22 when the serrations in the rows 20, 23 are interengaged, to provide a wedging action which urges the cable 19 to the bottom of the aperture 18, as viewed in Figure 1, and also provides a lead-in for the serrations in the row 24 when the wedge member 22 is introduced into the aperture 18.

The serrations in the row 20 are made up of surfaces which are generally normal to the axis of the cable portion within the aperture 18, and also of surfaces which are inclined to this axis, the latter surfaces being convergent towards the cable axis in a direction inwardly of the plug, so that the wedge member 22 canot move inwardly of the plug without also moving towards the row of serrations 21, and thereby increasing the clamping grip on the cable 18.

The serrations which form the rows 21, 24 lie in direction perpendicular to the axis of the cable 19 and are of saw-tooth form such that movement of the cable 19 in a direction outwardly of the plug will cause these latter serrations to bit more deeply into the cable sheath.

When wiring the plug, with the cover 11 removed, the cable 19 is placed within the aperture 18, as indicated in Figure 2, and the wedge member 22 is inserted from above, i.e. in the direction of the arrow 2 in Figure 1, in a position which causes the cable 19 to be firmly held by the serrations in the rows 21, 24.

The wedge member 22 is subsequently prevented by the cover 11 from moving upwardly out of this position.

The outer, mating edges of the base 10 and cover 11 are provided with interengageable rabbets 40, so that the base 10 and cover 11 may move away from their clamping inter-engagement by the screw 12, to at least the depth of the rabbets 40, without allowing any instrument to be passed into the plug through the side thereof. The base 10 is provided, as shown most clearly in Figure 5 with integral internal walls 41,42,43, the walls 41,42, also being shown in Figures 3 and 4. The walls 41,42,43 are of equal heights and extend above the side walls of the base 10. Afurther integral wall 44 has a height greater than that of the walls 41,42, 43 and has a portion which carries the row 21 of serrations on one side of the aperture 18. An integral cylindrical projection 45, having a through bore, provides a guide for the screw 12.The height of the projection 45 is substantially equal to that of the bottom of the rabbet 40 on the base 10.

A projection 46 engages a slot (not shown) in the wedge member 22 to limit movement of the latter transversely of the aperture 18. Awall 47 provides a stop which prevents the wedge member 22 being engaged with the base 10 in positions in which the serrations in the rows 20, 23 are not adequately interengaged.

As shown more clearly in Figure 6 the cover 11 has two integral internal walls 50, 51 which are of equal heights and which project above the sides of the cover 11. Two integral hollow cylindrical projections 52,53 respectively engage the inner surfaces of the shoulders 15,17 of the neutral and earth pins 13, 16, engagement of the projection 53 with the earth pin 16 being shown in Figure 3. An identical hollow integral projection 54 engages the terminal block 35, as indicated in Figure 3. The lengths ofthe projec tions 52,53,54 are such as to maintanthe pins 13,16 and block 35 in position on the base 10. The bores of the projections 52, 53, 54 receive the heads of the clamp screws on the respective shoulders 15, 17 and the block 35.

A hollow cylindrical projection 55 is integral with the remainder of the cover 11 and carries a threaded metal insert for receiving the screw 12. The projection 55 has a rabbet 56 which overlaps the projection 45 in the base 10 when the plug is assembled. A projection 57 is aligned with the projection 46 in the base 10 and engages a slot in the wedge member 22, in a like manner to the projection 46. Integral projections 58,59 engage respective ends of the fuse 32, as indicated in Figure 44, and ensure that the fuse 32 is retained by the clips 31,33. Additionally, the projection 58 engages the clip 31 and thereby prevents the clip 31 and line pin 14 from moving inwardly of the plug.

When the plug is assembled the walls 41,42,43 in the base 10 overlap the walls 50,51 in the cover 11, and this overlap, together with interengagement of the projections 45, 55 in the base and cover, define within the plug three compartments 60,61,62, indicated in Figure 5, which interconnect only through a zone adjacent the aperture 18. As indicated in Figure 4 with reference to the walls 43 and 51 the heights of the walls are such as to preserve the overlap even when the base 10 and cover 11 are parted by more than the depth of the rabbets 40. The internal walls restrict access to the internal connections of the plug, by way of the aperture 18, even when the base 10 and cover 11 are not fully interengaged. Moreover, the walls effectively prevent stray wires from faulty connections within the plug from causing a short circuit.

Afurther internal wall 63 on the cover 11 extends between the terminal block 35 and the fuse 32, so as to leave sufficient room only for the insulated line connection of the cable 19to pass between the walls 63 and the base 10. The probability of a stray conductor from the block 35 contacting the line pin 14 and thereby shorting out the fuse 32, is thereby minimised.

The internal walls also act the route the conductors of the cable 19 in such a manner that these conductors have equal lengths clear of the sheath of the cable, thereby facilitating the cutting and strip ping of these conductors prior to assembly.

Claims (14)

1. An electric plug including an insulating base having an aperture through which a cable can pass, and means within said aperture for clamping said cable to said base, said clamping means comprising a first row of serrations on a first side of said aperture, said first side of said aperture and an opposed second side thereof being convergent in a direction outwardly of said aperture, and a wedge member having a second row of serrations com plementaryto the serrations in said first row said wedge member having a face which is opposed to said second side of the aperture when said first and second rows of serrations are inter-engaged, said cable lying, in use, between said face of the wedge member and said second side of the aperture.

2. A plug as claimed in claim 1 in which said face of said wedge member is provided with a third row of serrations.

3. A plug as claimed in claim 1 or claim 2 in which said second side of said aperture is provided with a fourth row of serrations.

4. A plug as claimed in any preceding claim in which said face of said wedge member and said second side of said aperture lie in planes substantially parallel to the axis of a portion of a cable lying in use, within said aperture.

5. A plug as claimed in claim 4 in which said face of said wedge member is inclined to the plane of said second side of the aperture.

6. A plug as claimed in any preceding claim in which said first row of serrations comprises a plurality of surfaces which are substantially normal to the axis of a portion of a cable lying, in use, within said aperture, and a plurality of surfaces which are convergent towards said cable axis in a direction axially inwardly of said aperture, such that movement of said wedge member axially inwardly of the aperture is accompanied by movement of the wedge member towards said second side of the aperture.

7. A plug as claimed in any preceding claim which includes means for maintaining said wedge member captive on said base.

8. A plug as claimed in claim 7 in which said means for maintaining the wedge member captive includes a filament which is integral with said wedge member and which is secured to said base.

9. An electric plug including a separable insulating base and an insulating cover for said base, and means for clamping said base and cover together, said base and cover being provided with internal partitions which overlap when said base and cover are clamped together.

10. A plug as claimed in claim 9 in which said base and said cover have outer walls provided with rabbets which interengage when said cover and said base are clamped together.

11. An electric plug as claimed in claim 10 in which said internal partitions have heights such that they continue to overlap when said base and said cover are moved apart by the depths of said rabbets.

12. A plug as claimed in any of claims 9 to 11 in which said internal partitions co-operate to define three compartments within the plug, said compartments intercommunicating only by way of a zone adjacent an entry aperture for a cable, terminals for the plug lying within respective ones of said compartment.

13. A plug as claimed in claim 12 in which said partitions are positioned so that the lengths of conductor portions of said cable, between said aperture and respective ones of said terminals are substantially equal.

14. An electric plug substantially as hereinbefore described with reference to and as shown in the accompanying drawings.