Hi wizzards: I'm no familiar with power wiring and protection, since I am an electronic technician most familiar with milliamperes and millivolts. I need to shut and open a butterfly valve with an an electric actuator rated 16 A @ 120 VAC. No problem with the control scheme. My problem comes from the power side, since I have a 440 / 480 VAC supply (3 phase, 4 wire). I know I've got to take power from say phases A and B and go through a stepdown transformer. My questions: What should I use to protect the transformer on the 440/480 V side, fuses or circuit breaker ? Should I use another fuse(s) or C.B. on the 120 V side to protect the motor ?. The circuit must comply with American Standards (& practices) Thanks for your advice, I know it's peanuts for some of you out there

 

You have a couple of choices: You must protect the transformer from over current so if you fuse the primary side you have addressed this point. To protect the actuator you must fuse it accordingly. If you want to proect the transformer and the actuator from the primary side then you can choke the transformer by using a fuse smaller than the full load capability of the transformer. Calculate the load of the actuator at 480 volts to select the proper size fuse. Fuses or circuit breakers will work but fuses are usually more readily available in different sizes and therefore more flexible in application. Hope this helps.