general considerations when choosing power cable _ eep
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8/20/2019 General Considerations When Choosing Power Cable _ EEP
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General considerations when choosing power cable
General considerations when choosing power cable (photo credit: guanlite.com)
Copper or Aluminium?
Thousands of cable types are used throughout the world. They are found in applications ranging
from fibre-optic links for data and purposes through to EHV underground
power transmission at 275 kV or higher .
Certain design principles are common to power cables, whether they are used in the
industrial sector or by the electricity supply industry. For many cable types the
conductors may be of copper or aluminium.
The initial decision made by a purchaser will be based on price, weight, cable diameter,
availability, the expertise of the jointers available, cable flexibility and the risk of theft.
What to choose?
Once a decision has been made, however, that type of conductor will generally then be retained
by that user, without being influenced by the regular changes in relative price which arise from the
volatile metals market.
For most power cables the form of conductor will be solid
aluminium ,stranded aluminium , solid copper (for small
wiring sizes) or stranded copper , although the choice may
be limited in certain cable standards.
Solid conductors provide for easier fitting of connectors and setting of the cores at joints and
terminations. Cables with stranded conductors are easier to install because of their greater
flexibility, and for some industrial applications a highly flexible conductor is necessary.
Where cable route lengths are relatively short, a multi-core cable is generally cheaper and more
convenient to install than single-core cable.
telecommunication
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Single-core cables are sometimes used in circuits where high load currents require the
use of large conductor sizes, between 500 mm2 and 1200 mm2.
In these circumstances, the parallel connection of two or more multi-core cables would be
necessary in order to achieve the required rating and this presents installation difficulties,
especially at termination boxes.
Single-core cable
Single-core cable might also be preferred where duct sizes are small, where longer cable runs are
needed between joint bays or where jointing and termination requirements dictate their use.
It is sometimes preferable to use 3-core cable in the main
part of the route length , and to use single-core cable to
enter the restricted space of a termination box.
In this case, a transition from one to the other is achieved using trifurcating joints
which are positioned several metres from the termination box.
Armoured cables
Armoured cables are available for applications where the rigours of installation are severe andwhere a high degree of external protection against impact during service is required.
Steel Wire Armour (SWA) cables are commonly available although Steel Tape Armour (STA)
cables are also available. Generally, SWA is preferred because it enables the cable to be drawn
into an installation using a pulling stocking which grips the outside of the oversheath and transfers
all the pulling tension to the SWA. This cannot normally be done with STA cables because of the
risk of dislocating the armour tapes during the pull.
Glanding arrangements for SWA are simpler and they allow full usage of its excellent earth faultcapability. In STA, the earth fault capability is much reduced and the retention of this capability at
glands is more difficult. The protection offered against a range of real-life impacts is similar for the
two types.
cable type
http://electrical-engineering-portal.com/comparison-of-cable-insulating-materials
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