Connecting 3 wire cooktop to home 3 wire 240v
If that is indeed a 240V circuit, the white wire kinda shoulda been re-marked with tape to indicate that it is a hot wire.  Prior to about 20 years ago, they were allowed to skip the marking &quot;if the usage was obvious&quot;.  The reason for the change is that their &quot;obvious&quot; is not your &quot;obvious&quot;.
If you are confident that it is indeed 240V, remark that white wire with black or colored electrical tape.  (red is perfectly fine).

Code does not require you to mark different kinds of hot by their function... any hot can be any color not reserved for other things. *
White and gray are reserved for neutral.
Green, yellow w/green stripe, and bare are reserved for safety ground.
* with an extremely obscure exception relating to 3-phase power, that isn't even worth mentioning.