When you add an extension the resistance goes up and the heat generated goes up. You can't just keep adding length of the same size wire and it works the same. That's why it's well advised to use an extension with larger conductors of 12 gauge at a minimum and 10 gauge if you want to be extra safe.The factory cable is 14/3 and okay with 240V. We use a 25' 14/3 extension in the garage from a 240V welder socket with an adapter. No problems. All connections marked 240V because the extension end is regular 120V design.
Also, 240V doesn't really matter. It's the current (amps) that causes heat and potential issues.