MV design guide - Schneider Electric

Standards
IEC - ANSI comparison
c Operating voltage must fall within the following ranges:
Voltage
Voltage range (V)
Motor and closing release units
48 Vsc 36 to 56
125 Vsc 90 to 140
250 Vsc 180 to 280
120 Vac 104 to 127
240 Vac 208 to 254
Opening release units
24 Vsc 14 to 28
48 Vsc 28 to 56
125 Vsc 70 to 140
250 Vsc 140 to 220
120 Vac 104 to 127
240 Vac 208 to 254
Rated frequency
According to IEC
c Rated frequency: 50 Hz.
According to ANSI
c Rated frequency: 60 Hz.
Short-circuit breaking capacity
at the rated operating sequence
c ANSI specifies 50% asymmetry and IEC 30%. In 95% of applications,
30% is sufficient. When 30% is too low, there are specific cases (proximity
of generators) for which the asymmetry may be greater than 50%.
c For both standard systems, the designer has to check the circuit breaker
breaking capacity. The difference is not important because without taking
account of the asymmetry factor "S", it is equal to 10%.
ANSI: Iasym = Isym (1 + 2 A 2 ) = 1.22 Isym (A = 50%)
IEC: Iasym = Isym (1 + 2 A 2 ) = 1.08 Isym (A = 30%)
According to IEC
c Short-circuit breaking tests must meet the following 5 test sequences:
Sequence n° % Isym % aperiodic component
1 10 ≤ 20
2 20 ≤ 20
3 60 ≤ 20
4 100 ≤ 20
5* 100 30
* for circuit breakers opening at least 80 ms
Schneider Electric
Merlin Gerin MV Design Guide
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