Earthed and unearthed cables

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.

V.I.Abraham:

Any difference in construction of unearthed cable w.r.t earthed cable of same size?

Thanks,

BNDas

Hi Biswanath Das,

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. "

V.I.Abraham,

Thank you for the discussion. But I thing , say in case of 6.6kV earthed XLPE cable the insulation thickness is less than 6.6kV unearthed cable,since this cable will see 11kV voltage stress. This was the practice of manufacturer. But, presently they manufacture only one type, that is unearthed which is suitable for earthed system. This is to keep production lineup and inventory easy.

If u wanna differentiate between earthed and unearthed cable u have to differentiate them by the amount of insulation provided. Unearthed cables will have higher insulation than earthed cables. But also the point of neutral earthing also comes into picture.

Are you talking of shielded or c/w neutral? A cable with a neutral will have an increased dia. to accompany the extra wire. Kind of depends on what your doing. Do you need the return neutral? Delta or wye system? Fault protection? Grounding problem?

In normal condition there is no difference between earthed and unearthed system cable but at earth fault of one of the phase rise the voltage level of other phases from L-N to L-L even 5 to 6 time greater than that. so unearthed systems cable required higher insulation level.

Hello

I have answered your Post/comments,

Generally best to use the Cable Maker of your particular cable, but try:

http://relemaccables.com/

If you are still needing help, reply with

Kind Regards....

In normal system of Erath pahse to phase voltage is equal to line voltage and phase to earth voltage is Vph/ root 3. In unearth system the phase to earth will rasie to phase to phase voltage during the fault condition there fore need more insulation between conductor and earth screen. However in normal condition the stress on the insulation is very less as compare to normal earth system becasue the insulation thickness is high.

Due ti higher insulation thickness the reliability of the cables or the equipments are better. As those are understress .

The momentray voltage will be for a short duratio of time depend on the fault clearnce time.

Why unearth is used. If you earth directly the current will be high and to restrict the current flowing to the earth the resistance is used so that EPR earth potential rise will be less and we can give a sefety earth mats.

In circuits the fault clerance time is high the standing voltage on the phase to earth will become the equivalent to phase to phase voltage. As the voltage raise to 1.732 times the earlier phase to earth we need the higher insulation thickness. The falut clearing time is more so the SC current flowing to the earth will be more time which leads to rise in earth potential and to restrict the same the resistance grounding or the inductance grounding can be used.

As the time of fault clearnce is high the insulation is stress more. In normal condition these cables are operated well below the stress level.

Hi there,

Would I be able to use an earthed female cable (iec c13/c14) with an unearthed male port (iec c17/c18)?

Thanks

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