usually they state say 50A nominal with a short burst at a higher rate for a few seconds. Cable is made to withstand temporary short overloads, think the safety ratio is 2:1, don't ask me where I read that, it's a figure I've picked from the dark recesses of my mind. What kills cables is running at high loads for long periods of time, as that causes the cable to heat up and melt the insulation, hence heat resistant cable which we use for immersion heaters, for example, can carry a higher loading.