Hob wiring 5 core cable to 3 terminals
The L1, L2 and L3 terminals are separate for a specific reason: many countries in Europe (and some homes in the UK) have access to two-phase or 3-phase power, and 16A is a common breaker size on the continent. So in a larger home in Germany, for instance, this same hob would be connected to all three phases via a 3-phase, 16A breaker.  In that case 5-wire cable would supply all three phases, neutral and ground, that would hook up in the obvious manner.  

If your home has 3-phase, you too can split load like that, with appropriate breakers.  It really doesn't matter which of the 3 is connected to which phase, as long as the wire size and breaker is correct.  

Or in a 1-phase home, you can connect all 3 terminals to your one supply phase.  You will need to use a 45, 48 or 50A breaker, of course.