Hi all. I am currently building a 3DR quad, and am confused about the uses and requirements of ESCs with built in BECs .
The kit I purchased includes one ESC with built in BEC.
Should it be connected in a particular way?
What is it for?
Thanks in advance.
A BEC is used in an ESC to output a consistent voltage that you can use to power your RC gear (usually at 5V). Since both the APM and pixhawk use the APM power module to proive power to the flight controller you dont realy need to use the BEC. However once is included with your arducopter kit so that you can provide power to the output rail should you need to connect a servo to your system.
Thanks for your response. Does it need to be connected to a particular position on the Power Distribution board?
No it does not matter as the APM power distribution board merges all of the power/GND wires into a single +VE 
and GND 
wire