RULE 42 Query reversal of common ITC

As per Rul 42 clause (j) which read as under *the amount of credit attributable to non-business purposes if common inputs and input services are used partly for business and partly for non-business purposes, be denoted as ‘D2’, and shall be equal to five per cent. of C2*

Does it means only if i have business and non business usage Or even when i have exempt supply and taxable supply only without any non business supply do i need to work out under this clause.
Meaning thereby do disallowance under this clause to be worked out when there is only exempt supply along with taxable supply.