Cables

Question 1

Describe the construction of a STP cable used in CAT6 structured cabling system

Answer 1

1. consists of four pairs of insulated copper wire
2. Each pair is twisted together
3. Each par has a separate twist rate
4. There is an overall twist between all pairs
   5.There is a metallic foil/sheild wrapped around all pairs
5. There is an overall jacket

Question 2

Compare aluminium to copper conductors in terms of their mechanical properties, cost, current carrying capacity and conductivity

Answer 2

Cost. Aluminium is cheaper that copper

Current carrying capacity and conductivity. Aluminium conductor is only about 61% as conductive as the same size copper conductor, a higher cross section area is required for aluminium

Question 3

Describe the electrolytic effect between copper and aluminium cables that can occur and state the procedures for connecting copper to aluminium cables to prevent the electrolytic effect between the two cables

Answer 3

The electrolytic effect between copper and aluminum cables occurs when these metals are in contact, especially in the presence of moisture.

Use Specialized Connectors: Use connectors designed specifically for copper-to-aluminum

Question 4

State one type of cable suitable for installation in the soil with high impact resistant pipe in an industrial or commercial building and state the minimum depth it should be buried

Answer 4

1. SWA
2. At least 250mm below the surface

Question 5

Compare Aluminium to copper under the following headlines
1. Conductivity
2. Current carrying capacity
3. Mechanical strength
4. Cost

Answer 5

1. Conductivity. Aluminium is only about 60% of the conductivity to that of copper
2. Current carrying capacity. To carry the same as amount of current as copper a larger cross section area must be used
3. Mechanical strength. Aluminium only has about the third of the strength as copper
   4.Cost. Aluminium is cheaper than copper

Question 6

List 4 advantages of XLPE over PVC cables

Answer 6

1. XLPE is lighter
2. XLPE is smaller
3. XLPE has a longer service life
4. XLPE has a higher over load capacity

Question 7

State two precautions that should be taken when connecting aluminium cables onto copper busbar

Answer 7

1. Cable and busbar should be powered off
2. Cable and busbar should be clean

Question 8

List four precautions to be taken when installing data cables in an installation

Answer 8

1. Should be kept separate from power cables
2. Don’t crush or pinch cables
3. use proper cable ties/ don’t over tighten
   4 Don’t apply to much pressure when pulling cable

Question 9

List four methods of providing mechanical protection to cables that might be liable to impact on an installation

Answer 9

1. Steel conduit
2. PVC conduit
   3.Cable tray and basket
3. Steel trunking

Question 10

State any special protection conductor (PE) requirements that must be observed while using SWA in agricultural installations

Answer 10

The steel armour must not be used as the sole circuit protective conductor a core within the cable should also be used

Question 11

(A) It is proposed to install a non-armoured cable in a pipe in the soil state one acceptable type of piping suitable for installation in the soil

(B) The installation is planned for an industrial or commercial building state the minimum depth which it must be buried

Answer 11

A. PVP pipe having high impact resistance

B. 450mm below the surface in the soil once contained in pipe