Comma before nonessential clause ending a sentence

Is it correct to place a comma before a nonessential relative clause ending a sentence? For example

I met Katherine Jankowski, who is a world-renowned engineer.

Is the comma here correct?
I have been to told to avoid commas between an independent and a subordinate clause:

I took the bus because my car broke down yesterday.

not

I took the bus, because my car broke down yesterday.

Is this also correct?
I thank all helpers.