APPENDIX
72
NC020 - Manual - 05 - 2022
—
Phase overcurrent 50/51 - Standard inverse time curve (IEC 60255-3/BS142 type A)
F_51-IECA-Char.ai
1.1
2
3
4
5
6 7 8 9 10
20
I
RMS
/
I
>
inv
I
/
I
>>
inv
0.01
0.1
1
10
100
1000
10000
t
[s]
10 s
5 s
60 s
t
>
inv
t
>>
inv
1 s
0.5 s
0.2 s
0.1 s
0.02 s
t
=
t
>
inv
·
[(
I
RMS
/
I
>
inv
)
0.02
-1]
0.14
t
=
t
>>
inv
·
[(
I
/
I
>>
inv
)
0.02
-1]
0.14
Note: match of operating and setting time takes place when I/I>
inv
= 700