Whenever the question of building wiring is raised, one comes across the term ‘Armoured Cables’. After all, what is armored cable and why is it so important for electrical wiring systems. Let’s know about it.
Armored Cable Definition
Armored cable is a power cable made up by assembling two or more electrical conductors, generally held together with an overall sheath. This electrical cable with high protective covering is used for transmission of electrical power, especially for underground wiring needs. However, these cables may be installed as permanent wiring within buildings, buried in the ground, run overhead, or may even be kept exposed. They are available as single conductor cable as well as multi-conductor cables.
To be more precise, armored cables can be explained as electrical cables with stainless steel or galvanized wire wound over the conductors and insulation. They often have an outer plastics sheath for main distribution supply and buried feeders.
Why is Armored Cable Significant?
As can be made out from its name itself, armored cable is significant due to the ultimate protection it provides keeping in view the most risky job of electricity transmission. It acts as a circuit protective conductor (CPC) and thus provides earthing to the equipment supplied by the cable. However, its earthing capability has been a much debated subject.
Armoured Cable Earthing
A single conductor armoured cable does not have a ground wire. Its sheath is only for protection purpose. Therefore it is always recommended that one core armor cable should not be earthed on both ends. When both the ends are grounded, a “circulating sheath current” can flow between the armour, to ground then back to the armour. Grounding only one end is meant to allow bleeding of any voltage that might be induced into the sheath without creating a circulating current.
Single core armoured cables do not have magnetic fields generated by the other two phases. In a three phase cable, the sum value of the three magnetic fields is zero. In a single core cable, there is no “cancelling” effect and therefore a voltage will be induced in the armour by the magnetic field surrounding the conductor.
To prevent any kind of problem, a single conductor metallic armoured cable having lead, aluminum, stainless steel, steel or copper armors should be bonded to ground, usually at the source end, then isolated from ground along its length.
To know more about this power cable, read Armoured Cables