Wiring Confusion - 3 Phase Line to a Water Level Controller?
I certainly don't see any reason why not.    All the heavy switching is done by the contactor.  The controller couldn't care less what kind of current actually powers the motor: 3-phase, Japan 100V, hydraulics, pneumatics, Lackawanna 3000VDC, 4-phase early 1900s power, Detroit street lighting DC, clutchable drive shaft, warp plasma, or any darned thing you can find a contactor for.   

The contactor fully isolates the controller's voltage from the power that actually runs the pump.  

You do not hook multiphase mains (or air, or warp plasma) to the controller normally.  But in this case, you seem to have specced a 415V controller for some reason.  The only way to get that is to connect 2 phases line to line.   For that connection you will not use the third phase.  

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You actually have a problem here.  All the other wires here are phase wires.  The circuit from 15/18 to the contactor needs to be &lt;=250v otherwise you will exceed the rating of the relay.  That means you must use single-phase line to neutral (or really, anything the contactor can use, as long as it’s less than 250V). 

Now in this drawing, they have inelegantly shown taking the neutral from the pump mains supply. This is wrong in all cases and violates the "currents must be equal/balanced" rule.  As you know, current flows in loops, that is a very bad loop!  

Normally I would say "The contactor coil should get its neutral from controller supply, e.g. from A2 on this drawing".   But in this case, your controller will need 415V line-line, and so neutral will not be present.

If this is "wye" power you may be able to bring over neutral.  If it is "delta" power simply use a different circuit.  

If the relay coil is 415V you cannot use iqt because 415>250. Regardless, you need a 3-pole contactor, because it's 3-phase. 



* to those who believe all 3-phase delta is "240V wild leg delta" with neutral centered on a leg, this is Europe and there's no such thing.  Also even in America not all 3-phase delta is that.