GB2166304A

GB2166304A - Wiring electrical plugs

Info

Publication number: GB2166304A
Application number: GB08526268A
Authority: GB
Inventors: Raymond Grasby
Original assignee: Legrand Electric Ltd
Current assignee: Legrand Electric Ltd
Priority date: 1984-10-26
Filing date: 1985-10-24
Publication date: 1986-04-30
Also published as: GB8526268D0; GB8427153D0

Abstract

An electrical plug, for example a 13 amp, 3-pin plug, has pins with differently coloured sleeves round them. The sleeves may correspond to the colours of the wires to be attached to the individual pins, so as to avoid errors in wiring the plug up. Each sleeve may be a heat-shrunk plastics sleeve, moulded on or premoulded.

Description

SPECIFICATION Wiring electrical plugs This invention relates to wiring electrical plugs.

In order for electrical apparatus to work properly, it is essential that plugs and sockets are wired correctly. This is of particular importance in mains electrical systems where the improper connection of wires, e.g. connecting the wrong wires to the wrong pins in a standard domestic electrical plug, can have dangerous results.

The wires in a multi-conductor cable are generally colour-coded by the application around them of differently coloured plastics sheaths in oder to distinguish them one from another and enable connection to the appropriate terminals in a plug.

Selection of which terminal to connect each wire to is usually on the basis of its position or on the basis of markings usually moulded into the plug casing or base and which may take the form of letters or words.

One particular area of interest is the domestic electrical plug, in the U.K.a standard, 13 amp, 3-pin plug of the type described in British Standards Specification 1363. By convention, the three pins are described as earth, live and neutral pins, the earth being somewhat longer than the live or neutral, and with the neutral pin being invariably unfused and located below the earth pin to the left when the plug is held with the pins facing away from the person holding it. Typically the letters E, L and N are moulded on the interior and/or exterior of the plastics casing of the plug. Occasionally the conventional colours are also indicated on the plug, though more often the correct standard wiring colours are mentioned on a printed card attached to the plug or on a label attached to the wire, e.g. the mains lead of a domestic electrical appliance.

Despite such markings and labels, plugs are frequently miswired, with consequent dangerous results.

The extent of miswiring has increased in recent years following standardisation. Old U.K. wiring used to use red, black and green coloured sheaths.

Red is traditionally used to indicate danger and corresponded to the live wire. Green was associated with "earth", and the black wire was the neutral line. When the colours changed some years ago, the "red = danger" allusion disappeared, and people have much greater difficulty in remembering blue = neutral, brown = live.

According to the present invention there is provided an electrical plug having a plurality of contact pins for insertion into a socket, the pins projecting from a base member, some or each of the pins being partially surrounded by a sleeve of coloured plastics material, the sleeves on at least some of the pins being different colours.

Preferably the colours of the sleeves correspond to the colours of wires to be attached to the pins.

Thus, for example, a 3-pin, 13 amp plug may have its live pin provided with a brown-coloured sleeve, and its neutral pin with a blue-coloured sleeve.

The sleeve may extend along the pin for a greater or smaller distance. Normally the end of the pin remote from the base will be left bare in order to make appropriate electrical contact in a socket, with the sleeve surrounding at least the middle of the pin's length. In a highly preferred form of the present invention the sleeve extends from just within the base member towards the distal end of the pin and is made of an electrically insulating material. Such a sleeve may then have the dual function of indicating which wire goes with which pin and providing an enhanced measure of electrical safety by sleeving the majority of the pin's length. Sleeves have been applied for electrical safety purposes for some years, and are described inter alia in British Patent Specifications 327,993, 1,181,370, 2 040 600 and 2 067 028.

The coloured sleeves on plug pins according to the present invention may be applied by any of the known methods such as moulding plastics material around a pin, heat-shrinking a coloured plastics sleeve on to the pin, applying the sleeve by fluidised powder coating or putting a preformed moulded sleeve over part of the pin's length. The plastics sleeving should meet appropriate technical requirements (e.g. as in B.S. 1363) and be made of suitable material, e.g. Nylon or alternative material having suitable properties. Such sleeves may easily be manufactured in a variety of colours. For most applications, the sleeve will be in a recess on the main body of the pin, either a formed or machined recess in the case of a solid pin, or a formed recess in the case of a pin formed by folding from hollow blank.The surface of the sleeve should normally be flush with the surface of the unsleeved portions of the pin in order to minimise problems on insertion and removal of the plug from its cooperating socket.

While the present invention may be used in a wide variety of plug types, it is of particular value in connection with domestic 13 amp plugs and according to a specific feature of the present invention there is provided a domestic electrical 13 amp plug comprising a plug base and three projecting pins for the connection of earth, neutral and live conductors thereto, the live and neutral pins being surrounded for a portion of their length extending from just within the base towards the distal end thereof with a plastics sleeve, the sleeve surrounding the neutral pin being blue, the sleeve surrounding the live pin being brown.

It is found that colour coding the pins in this way is highly effective in ensuring that plugs are wired up correctly. The colour identifications of the pins are clearly visible to the person wiring the plug and in almost all cases will correspond directly to the colours of the plastics sheaths surrounding the conductors in the mains cable to which the plug is being attached.

The use of moulded sleeves in a suitable thermoplastic material around the live pin is of particular value in 13 amp square pin plugs where the live pin takes the form of a conductor pin which is split from one end, the free ends of the two legs thereby formed being configured to receive and re siliently grip one end of a fuse between them. In such pins, the slot extends usually some way from one end towards the other, and accordingly the two legs can be levered apart if a fuse is inserted at a skew angle. Putting a sleeve around part of the length of the pin, which sleeve effectively bridges the slot on both sides of the pin, makes the arrangement stronger and enhances the resilient grip of the two ends of the legs of the pin on the contact cap on the end of a fuse.

Claims

1. An electrical plug having a plurality of contact pins for insertion into a socket, the pins projecting from a base member, some or each of the pins being partially surrounded by a sleeve of coloured plastics material, the sleeves on at least some of the pins being different colours.

2. An electrical plug according to claim 1 and having a red or brown coloured sleeve on a live pin thereof,

3. An electrical plug according to claim 1 or 2 wherein the sleeve extends from just within the base member towards the distal end of the pin and is made of electrically insulating material.

4. An electrical plug according to any one of claims 1 to 3 wherein the or each sleeve is provided by moulding plastics material around the pin.

5. An electrical plug accordingly to any one of claims 1 to 4 wherein the pins bear moulded sleeves of differently coloured nylon plastics material.

6. An electrical plug according to any one of the preceding claims wherein the surface of the sleeve is flush with the surface of the unsleeved portions of the pin.

7. A domestic electrical 13 amp plug comprising a plug base and three projecting pins for the connection of earth, neutral and live conductors thereto, the live and neutral pins being surrounded for a portion of their length extending from just within the base towards the distal end thereof with a plastics sleeve, the sleeve surrounding the neutral pin being blue and the sleeve surrounding the live pin being brown.

8. A domestic electrical 13 amp plug according to claim 7 wherein the live pin is split from its end closer to the base to form two legs which are adapted to resiliently grip the contact cap at the end of an electrical fuse, and the plastics sleeve surrounds part of the split portion of the pin.