Use of comma before "Which" and "When"

When do I have to use a comma before “Which” and “When”? :roll:

Use a comma before ‘which’ when it introduces a non-restrictive subordinate clause. Offhand, I don’t think I ever use a comma before ‘when’.


You might be interested to read some material I’ve written for the site on the use of the relative pronouns -


:lol: Thank you for your explanation