Medium Voltage Application Guide

SWITCHGEAR
Rated peak withstand current (kA)
This is the maximum peak fault current level which the device is able to close (make) on. This rating must be
greater than the expected peak let-through fault current (I p ) at the point of installation.
Rated peak withstand current ≥ I p
I p = 2.5 x I s (for a 50 Hz supply with a
45 ms DC time constant)
I p = 2.6 x I s (for a 60 Hz supply with a
45 ms DC time constant)
Source: IEC 62271-1, IEC 62771-100
Where:
I p = asymmetrical peak let-through fault current, from the first fault
loop (kA)
I s = rms symmetrical fault current level, with no DC component
(kA)
MV earth switches tend to have a maximum I p of 82 kA.
Electrical endurance class
This class defines the fault making capability of earth switching devices.
E0 (Standard electrical endurance): No fault making capability
E1 (Extended electrical endurance): Capable of 2 fault making operations without damage
E2 (Highest electrical endurance): Capable of 5 fault making operations without damage
Mechanical endurance class
This class defines the mechanical endurance of no-load disconnectors.
M0 (Standard electrical endurance): 1000 operating cycles without maintenance
M1 (Extended electrical endurance): 2000 operating cycles without maintenance
M2 (Highest electrical endurance): 10000 operating cycles without maintenance
710-12280-00A Medium Voltage Application Guide Page 103