Coul/cut or coul/long

Hi all
How do we determine whether to use lj/cut/coul/long or lj/cut/coul/cut for a charged system??

I saw in a previous mail that we have to use long range interactions for CO2, SPCE water system etc. What about Na+ ions?

In my system when I use long range Coulombic interactions, Na+ ions are moving outside the boundary through the walls. I just tried with coul/cut and it works fine (because of obvious reason). So is it correct if I keep using coul/cut for these ions? Is there any guidelines to determine it?

Thanks in advance!

The basic rule is that if the original force field used long-range electrostatics, so should you.