Rated Short-Circuit Making Current

Can anyone please tell me what “Rated short-circuit making current: stand for? E.g Rated short circuit breaking capacity is 25kA, while the Rated short circuit making capacity is 62.5kA.


On breakers there is a difference between what the main contacts can interrupt, once, and what the contacts can carry without interrupting. And it would be the same for bus bar in that it has a carry capacity.
The carry capacity is typically a I^2T function and the ability to dissipate heat and remain below the melting temperature.
The interrupting rating is the ability of the main contacts to handle the arc interrupting on the current for one operation. If the breaker is expected to interrupt a fault more than once between contact replacements it needs to have a greater interrupting rating to allow for the contact wear factor.
Also you will find there should be an additional rating called the capacitor switching rating, which is a measure of the contact speed and opening distance and the ability to operate with near 90 degree angular difference between the current and voltage.

Above is a snippet.

If a switch or breaker is used to interrupt a current greater than its ability, bad things happen.
If the current is greater than the interrupting capacity of the device then opening the device may result in a sustained arc and the possibility of the destruction of the device and collateral damage.
The fault that is causing the current may not be cleared.
Many switches and breakers can withstand a pass through current greater than their ability to interrupt, but they cannot be used to interrupt that current.
There must be other devices in the circuit that will safely interrupt fault currents.

1 Like