IEC Cable Rating Explanation (e.g. what does 3.6/6 kV mean?)

[bp168]

Hello,

What do the following cable ratings mean?
3.6/6 kV
6/10 kV
8.7/15 kV

I believe that they are IEC cable ratings, but what do the two numbers mean? What is the maximum voltage the cable is designed to handle?

Just to give some background, I'm looking for cables suitable for applications at 5 kV, 8 kV and 15 kV. So would I be able to use a cable rated 3.6/6 kV for 5 kV, 6/10 kV for 8 kV and 8.7/15 kV for 15 kV?

Thanks for the help!

 

[ScottyUK]

Voltages quoted are the working voltages line-ground and line-line respectively. Thus a 6350/11000 cable is suitable for an earthed system, but inadequate for a non-earthed system where one pole could be grounded without the circuit being automatically disconnected by the protection scheme, causing line-line voltage to exist between two of the three conductors and earth for a long period. This latter system is (I think) more common in North America - the UK rarely uses ungrounded installations, and the little bit of European MV practice I'm aware of similarly tends to use solid or impedance grounding.

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[cuky2000]

The IEC designation for cable voltage rating is :Uo/U (Um),
_{Where:
Uo = max phase-to-ground voltage
U = max. Line—to-line-voltage
Um = maximum system voltage.}

Here is a typical example of cable rating

‘Designation: 10 kV 15 kV 20 kV 30 kV 50 kV
Uo/U: 6/10 kV 8,7/15 kV 12/20 kV 18/30 kV 36/50 kV
Um 12 kV 17,5 kV 24 kV 36 kV 72,5 kV