to the 16th Edition IEE Regulations
   
   
   
 
 

chapter 5
Earthing

chapter 6
Circuits

Data cabling and networks
  9.1 - What is data cabling and why do
------- we need it?
9.4 - System design and categories

  9.2 - What are digital systems? 9.5 - Installing data cabling
  9.3 - Copper or glass fibre? 9.6 - Useful information


9.3 - Copper or glass fibre?

Since they involve little cabling, wireless systems will not be considered here

Copper cabling exists in two major types, the unshielded twisted pair (UTP) and the shielded twisted pair (STP). Coaxial cable is used in special applications where radio and television signals are carried. UTP cables usually consist of four twisted pairs of wires enclosed in an overall sheathing. To reduce interference, each pair has a different number of twists per unit length. These cables can be used for alarm systems and voice-only telephones (category 1) at the lower bandwidths, up to data applications up to 100 MHz (category 5). Higher frequency cables have more twists in a given length.

Unshielded twisted pair cables may be susceptible to radio and electrical interference, this disadvantage being reduced in the shielded twisted pair (STP) cable. The shielding (of braiding or of foil) increases the size and the cost of the cable, and also requires effective earthing (in the USA they call it grounding). STP cables may also have greater loss at higher frequencies, and are more expensive, both to purchase and to install, not only because they are larger, but because shielded connectors must be used. In simple terms UTP cables are adequate for situations where there is unlikely to be interference from fluorescent lighting and machinery such as motors, welders, and so on.

Fibre optic cables (in the USA they spell it fiber) have a very thin core of glass (usually ultra-pure fused silica) with a protective sheath. Light is injected into the cable by a laser or light-emitting diode, and changed back to an electrical signal at the receiving end by a photocell. The fibre-optic cable is able to carry signals over greater distances than are copper cables, and at greater speed; it can also be used over a greater bandwidth. Since it is not an electrical system, it is immune from electromagnetic and lightning interference. Other advantages over copper cabling are vastly increased signal capacity (due to the very high frequency of light), lower transmission losses, lower cost of basic materials and much smaller cable size. The reduced transmission loss can often allow simpler networks, by having only one central point of administration with all data cabling fed back to it. At the time of writing, fibre networks are still more expensive than those with copper cables, but the gap is narrowing. For very high bandwidth applications fibre networks are the only solution. Category 5 systems can operate with copper cables, but some think that they are better served by fibre optic systems. It seems likely that when categories 6 and 7 arrive they will need fibre to support them.

 

 

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Extracted from The Electricians Guide Fifth Edition
by John Whitfield
Published by EPA Press Click Here to order your Copy

Click here for list of abbreviations