Understanding current, wire size, and voltage drop
Voltage drop is one consideration, there are others. 

Think about the potential fault current and fusing for that circuit. 

You want the wire to be sufficiently large gauge to be able to blow the fuse or trip the breaker without causing a hazardous situation (such as the wire going incandescent). In many cases that may be prescriptively spelled out by safety regulations (NEC, UL or whatever). 

There may also be minimum gauge requirements just for mechanical robustness (for example AWG20 is the minimum wire gauge allowed in some situations).