Minimum
By today's NEC standards, all kitchens are required to have to have a minimum of two 20 amp circuits.
It is a set of standard practices called the "National Electrical Code"
There is no minimum height specified by the NEC.
National Electrical Code (NEC)
NEC Book each state uses different year codes
I assume your sizing the 20 amp from the breaker? NEC 240.3 states minimum conductor size for the rated ampacity of the circuit breaker. In this case, minimum size for 20 amp breaker is 12 AWG. I assume you are wiring a motor? I suggest you size your over current in accordance with NEC, start reading around NEC 430.
According to the NEC (national electric code) a maximum of 2% voltage drop is allowed.
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