Electricity: conductors and insulators – Conduits – cables or conductors – Conductor structure
Patent
1992-12-21
1994-07-12
Nimmo, Morris H.
Electricity: conductors and insulators
Conduits, cables or conductors
Conductor structure
174113R, 174115, 174116, H01B 700
Patent
active
053290658
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electrical cable or flex and in particular to a high voltage electrical cable.
BACKGROUND ART
In the supply of electricity to certain electrical devices it is often necessary for the cable or flex used to withstand an initial high electrical voltage which is used to commence operation of the device, which thereafter runs on a standard mains voltage. For example, in order to strike a mercury vapour lamp or other similar lighting means, it is necessary to supply an initial voltage of approximately 4,500 volts. If a standard 3-core 13 amp electrical cable is used to supply this voltage, the cable can cope initially but quickly becomes burnt out with repeated use. There is also a significantly increased risk of fire.
To overcome the problem of supplying an initial high voltage to devices, such as lamps, which then run on a standard mains voltage, a heavy gauge single core insulated cable is often used as the live wire of the electrical supply along with separate standard single core neutral and earth wires. When wiring such a device to a mains electric supply these three wires are often pulled into a hollow sheath or tubular casing by the electrician so that the resulting single flex can be threaded, as appropriate, down a conduit between the electrical supply and the location of the device. However, it will be appreciated that this considerably increases the work required by the electrician as compared with the wiring of a device capable of being supplied by a standard 3-core cable. In addition, the sheathing of the three separate wires in the outer casing is often difficult to accomplish satisfactorily as the casing tends to twist and wrinkle.
The object of the present invention is to overcome or substantially mitigate the aforementioned problems.
SUMMARY OF THE INVENTION
According to the present invention there is provided a multi-core electrical cable comprising a moulded-on outer sheath, at least two separately insulated inner core cables and a separately insulated earth cable and characterised in that at least one of the inner core cables has a high tension conducting core with an overall cross-sectional area of at least 1 mm.sup.2 and an insulating sheath which is approximately 1.8 mm thick, and in that the earth cable has a conducting core with an overall cross-sectional area of at least 1 mm.sup.2 and an insulating sheath which is approximately 0.65 mm thick.
Preferably, the high tension conducting core comprises a bundle of at least 32 strands of 0.2 mm diameter tinned copper wire.
Preferably also, the moulded-on outer sheath of the multi-core cable totally encapsulates the inner core cables and the earth cable to a depth of at least 1.3 mm.
Preferably also, the inner core cables and the earth cable are twisted together within the moulded-on outer sheath and bound by a spirally wound tape.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described by way of example with reference to the accompanying drawing, in which:
FIGS. 1 and 1a are side and end views respectively of a high tension core cable for incorporation into a multi-core cable according to the invention;
FIGS. 2 and 2a are side and end views respectively of an earth safety core cable for incorporation into a multi-core cable according to the invention;
FIGS. 3 and 4 are side views of three core cables forming part of a multi-core cable according to the invention at two stages respectively during its manufacture;
FIG. 5 is a side view of a multi-core cable according to the invention with part of its outer sheath cut away to reveal the core cables; and
FIG. 6 is a transverse cross-sectional view of the cable shown in FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
The multi-core cable of the present invention comprises at least one inner core cable 1, as shown in FIG. 1 and 1a, which is capable of withstanding a high voltage, preferably of at least 4,500 volts.
This cable 1 comprises an insulating sheath 2 encapsulating an inner conducting core 3 which is made
REFERENCES:
patent: 2286826 (1942-06-01), Morrison
patent: 2958724 (1960-11-01), Milloit
patent: 3614300 (1971-10-01), Wilson
patent: 3710009 (1973-01-01), Hoeg et al.
patent: 4543448 (1985-09-01), Deurloo
patent: 4657342 (1987-04-01), Bauer
Hardy David
Marney Derek
Litetronics (U.K.) Ltd.
Nimmo Morris H.
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