Why changes to /etc/limits doesn't work

Why changes to /etc/limits doesn't work

I am trying to provide support for core dump on my ARM based target ,I
have read about both /etc/limits and /etc/security/limits.conf ,My target
file system doesn't have the later one on to it ,So I have made below
changes to /etc/limits
root C100000 After adding this line to /etc/limits was expecting the
generation of core file but ulimit -a shows me
core file size (blocks, -c) 0
Why these changes into /etc/limits does not at all reflecting.
Now what should I have to do ?
Do I have to add /etc/security/limits.conf to my filesystem??
I am not looking at option of using setrlimit().