Fault rating Fault rating Indy (Industrial) (OP) 28 Jul 17 13:58 Hi We have a switchboard and the name plate reads 50kA for 1 sec. just to clarify that the 50kA is the prospective phase fault current. Thanks RE: Fault rating waross (Electrical) 28 Jul 17 14:22 Not quite. That may be the Available Short Circuit Current rating. With an available ASCC of 50 kA, the actual first cycle fault current transient in an inductive circuit (High transformer X/R ratio) may approach 141 kA. A rating of 50 kA indicates that the equipment will withstand the mechanical forces associated with an ASCC of 50 kA. A rating of 50 kA for 1 sec may include the damage curve as well. Best to check with the manufacturer as to whether the 50 kA is the maximum DC offset current (Maximum transient) or the ASCC. Bill -------------------- "Why not the best?" Jimmy Carter RE: Fault rating 7anoter4 (Electrical) 3 Aug 17 15:27 IEC 60694 Common specifications for high-voltage switchgear and controlgear standards 4.5 Rated short-time withstand current (Ik) The r.m.s. value of the current which the switchgear and controlgear can carry in the closed position during a specified short time under prescribed conditions of use and behaviour. 4.7 Rated duration of short circuit (tk) The interval of time for which switchgear and controlgear can carry, in the closed position, a current equal to its rated short-time withstand current. The standard value of rated duration of short circuit is 1 s.