Cable Insulation

How much is the difference in insulation for earthed and unearthed cables?

what do u mean by unearthed cable? a cable that is not grounded, but hanging to device?

You can always put an insulation on an earth cable too, like a live wire. But even if you don't it doest matter so long it is grounded properly with the correct material and correct diameter of wire is selected.The only purpose of putting insulation can be to avoid any contact of earth wire with the any other live wire.

why does an earthed system require less insulation?

Because it remain on Zero potential,

Why do people not follow earthing system as mandatory?

Because they are Dizzy and don't realise that earthing is made for them.

What is the reason for making thin isulation on the conductor for XLPE cables which are called unearthed?

Dear muralinam,

This subject was discussed twice earlier in this forum. Please read all replies dated 08/21/2008 on the same subject. Here I quote one of my earlier replies for your benefit

"

In HT electrical distribution,the system can be earthed or un earthed.

This same subject was discussed for a thread that came up in CR4 on 04/01/2008 . Please read my reply which is quoted below and please read all the other replies . It is always better to check the previous threads on the same subject before putting up a new thread.

"The selection of earthed/unearthed cable will depend on your system. If your distribution system is earthed then you have to use cable manufactured for earthed system. (which the manufacturer specifies). If the system is unearthed then you need to use cable manufactured for un earthed system.The unearthed system requires high insulation level"

"

For earthed and un earthed XLPE cables, the IS 7098 part2 1985 does not give any difference in specification. The insulation level for cable for unearthed system has to be more. In simple statement the manufacturers states that 11 KV earthed cable is suitable for use in 6.6 KV unearthed system.The process of manufacture of cable is same. The size of cable will depend on current rating and voltage level.

what IS specifies and I quote below:

" b) Voltage Grade (Uo/U)

1) Earthed System - 1.9/3.3 kV, 3.8/6.6 kV, 6.35/11 kV, 12.7/22 kV and 19/33 kV.

2) Unearthed System - 3.3/3.3 kV and 11/11 kV.

Note 1 - Cables of 6.35/11 kV grade (earthed system) are suitable for use on 6.6/6.6 kV (unearthed system) also "

They don't follow the earthing system out of greed or ignorance.