Q1] What do these numbers refer to?
A1] Standard cable nomenclature based on IEC Std 183 used to designate cable voltage rating as follow:
Uo/U (Um)
Were
Uo = rated rms power frequency voltage, core to screen or sheath ~(VLN)
U = rated rms power frequency voltage, core to core. (VLL)
Um = max. rms power frequency voltage, core to core. (max VLL ~1.05 to 1.10 VLL)
Q2] How does it relate to the North American 100%/133% ratings?
A2] Even though there is not a through equivalent IEC also provides 3 categories similar to 100% 133% and 173% as follow:
-100% time to remove fault < 1 min ~ CATEGORY A: Phase conductor in contact with ground fault is automatically disconnected from the system.
-133% time to remove fault < 1 hr ~CATEGORY B: Under fault condition, a cable will operate for short time (<8hrs) with one phase grounded without exceeding 125 hr during 12 months period.
-173% continuous time ~ CATEGORY C: System that does not fall into category A and B.