169
NC20 - Manual - 01 - 2015
APPENDIX
Phase overcurrent 50/51 RMS - 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
0.01
0.1
1
10
100
1000
10000
t
[s]
t
>
inv
= 10 s
t
>
inv
= 60 s
t
>
inv
= 5 s
t
>
inv
= 1 s
t
>
inv
= 0.5 s
t
>
inv
= 0.2 s
t
>
inv
= 0.1 s
t
>
inv
= 0.02 s
t
=
t
>
inv
·
[(
I
RMS
/
I
>
inv
)
0.02
-1]
0.14
Note: match of operating and setting time takes place when I
RMS
/I>
inv
= 700
