The thermal time constant T of a resistor indicates how fast its temperature may rise under certain operating conditions. After 1T, it has reached about 67% of the final temperature and after 5T it has more or less reached its final temperature. The time constant is dependent on the resistor type and mass, on the size of the surface and on the cooling system. The higher the time constant of a resistor the higher its short-term overload capacity whereby – depending on the design – the maximum pulse load resistance also has to be considered which does not have to be directly dependent on the time constant. With their large mass, GINO cast iron resistors exhibit particularly high time constants and thus a high overload capacity.