On dilution, the molar conductivity of a strong electrolyte solution:

Strong electrolytes are already fully dissociated even in concentrated solution. On dilution, the only change is a reduction in interionic interactions, which increases ion mobility slightly. So $\Lambda_m$ rises slightly with dilution and reaches the limiting molar conductivity $\Lambda^\circ_m$ at infinite dilution. Weak electrolytes, in contrast, undergo a large rise in $\Lambda_m$ because the degree of dissociation itself rises with dilution.