10-30 words

[1]        What is the arrangement adopted for laying cables to minimize magnetic interaction?

The cables are as far as practicable are kept at right angles to each other and also for the physical proximity, they are kept at a distance from each other.

  30-60 words

[1]        What is armoring in a cable?

Extra mechanical protection provided by armoring with woven wire braid made of galvanized Steel or tinned phosphor bronze. Steel armoring is not preferred for single core cables carrying Heavy alternating currents because of magnetic properties.

[2]        What is meant by current rating of a cable?

The passage of current through a cable conductor results in rise of temperature due to resistance of the conductor. Therefore maximum current rating is based upon maximum operating Temperature of the insulation and sheathing’

[3]        Comment on the requirements of conduits in regard to cable installation?

1. Cable outlets from conduits should be bushed to prevent abrasion at the ends’
2. Total cross sectional area of cables should be less than 40vo of the cross-sectional on Conduit.
3. Ventilation of conduits should be provided, and it should be ensured that water does not collect in the conduit’
4. The conduit should be earthed’

  100-150 words

[1]        Subjected to over voltage due to seasoned or intermittent fault. with respect to silicon rubber insulated cables briefly discuss :

(a)        Its advantages

(b)        Its disadvantages.

Advantages of silicon rubber insulated cables:

Silicon rubber has outstanding resistance to high temperature.

It can continuously operate at temperature up to 150ºC.

In case of fire, it burns to form silicon oxide which is an electric insulator. Hence, operation can continue even after a fire, provided conductor is not melted.

It is not mechanically robust, but remains flexible down to very low temperature.

However, modern grade has adequate mechanical strength to withstand rough handling.

Disadvantages:

Not oil resistant. Hence sheathing of glass braiding with heat resisting varnish needed.

It is very expensive and only used for special applications.