Voltage rating of power cables?

Umax is the maximum permissible continuous over voltage.

Thanks Biswanath, but, does it make sense?

The voltage rating for an electrical aparatus is (by difinition) the ceiling of this parameter for it to operate safely.

I guess a cable maximum permissible continuous operating voltage is enough for a user to be respected as it is bigger than U_o/U_n . i.e. if the 1^st. is given, the 2^nd. is useless. Do you agree?

Regards... Samak

The insulation is calculated on the peak voltage not the rms, which is what you get when you touch it, so beware!

Sorry!!!

The given value in Siemens Catalog as I said in the example doesn't match your answer.

U_max=7.2 KV

U_o=3.5 KV

U_n=6 KV

However, U_n = √3 U_o ,

but unfortunately, U_max ≠ √2 U_n.

Regards... Samak

You are quite close to the answer:

U₀ is the voltage between the lines and the earth and neutral conductor.

U_n is the voltage between the lines.

U_max must be the absolte maximum application of the cable, when no voltage differences between the conductors are present.

Find IEC 60183 and IEC 60885-3, Uo-U-Umax all defined inside, about partial discharge test dan voltage test.

Hi Samak, responding to your message on "Question for experts", but I'm not sure I can add much to this. Quoting both U_o = 3.5 and U_n = 6 kV = U_o x √3 is redundancy, as you say, but I suppose it's better to have too much info than not enough! We sometimes in UK refer to 230/400 volt.

Agree with your response to #3, I was thinking that before I read yours. I can only assume that U_max 7.2 kV is rms value, so cable can stand √2 x that as a peak on a AC supply (ie not necessarily on a continuous basis).

I don't understand Gwen's #5 (last line). Perhaps it's just wording. I assume U_max (rms) voltage difference must not be exceeded, whatever the actual values on the phases are. But U_max relates to the complete cable, so max actual voltage is U_n. Can you clarify please Gwen?

Cheers.....Codey

As I tried to explain: U_o and U_n are pointing to the potential difference between the lines in the cable, typical for tri faze setup.

U_max relates to the absolute level a cable can be used. Nothing to see with the peak-peak values and the line differences.