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Fault rating

Fault rating

Fault rating

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.


RE: Fault rating

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.

"Why not the best?"
Jimmy Carter

RE: Fault rating

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.

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