How do 4-20 mA receivers work?
They are many loop powered sensors, so it is possible that you may need only 2 wires to the sensor. You have not included details to your sensor so it's hard to know what you have. 

Providing the sensor consumes no more than 4 mA, it can be designed to be line powered. If it requires more than 4 mA then it must be locally powered (typically AC powered) and the 4-20 mA loop becomes simply the data loop.

These articles may help you:
This is a basic article on 4-20 mA loop technology
...and this is the datasheet for a loop powered vibration sensor.

Typically the receiver is also the location of the loop power supply (the sensors are the remote part), so the receiver will have both loop and power wires.