What are the Rated short-circuit making capacity (Icm) and Rated short-time withstand current (Icw) values of Compact NSX Switch-disconnectors (NSX xxx NA)?
30 September 2021
Rated short-circuit making capacity (Icm) and Rated short-time withstand current (Icw) values for Compact NSX Switch-disconnectors can be found in Compact NSX Catalogue.Icw and Icm values are defined by IEC60947 standard as following:Icw is the value of RMS current that can flow through the disconnector for a given time without causing damage to the device.
Icm is the peak value of short circuit current that the disconnector can close to, if closing on a fault without being damaged.Please see the following characteristic from the NSX Catalogue:For example, Icw value of NSX400 NA is 5000A/1s, that means NSX400NA can withstand 5kA/1s.Please note that NSX switch disconnectors can’t withstand any other higher values which are not mentioned under Icw for 1 second.The greater Icm value (330 kA) is related to the case when the disconnector is combined with upstream current limiting circuit breakers while the lower value is for switch-disconnector alone.It is mandatory to use a circuit breaker upstream of them for protection against overloads and short circuits.However, the Compact NSX NA switch-disconnectors are self-protected (i.e. they have a certain magnetic tripping threshold.), as noted on the catalog page. NSX NA is self-protected as soon as the switch is closed.This function is ensured by a magnetic protection inside the switch.The THRESHOLD self-protection by their high-set magnetic release are: - 10kA for the NSX100NA till NSX250NA - 15kA for the NSX400NA till NSX630NAIt is only an integrated partial protection to avoid contact repulsion and it could not be used for network protection.
We have no characteristic graphs for the self-protection by high-set magnetic release, because it is not a performance value for customer application.