I have a service enclosure (with ground rod) that feeds highway lighting from one breaker, and a subpanel from another breaker. The subpanel is another service enclosure (with ground rod) about 400' away serving a freeway changeable message sign. The voltage remains 120/240 in both services. My question is, do I need to include a fourth ground conductor between the service and subpanel if they both have a ground rod? The conduit between the two is schedule 40 PVC. Thanks in advance!
You only have one service, the first location after the POCO supply. The second location is supplied by a feeder if it comes from the first location. Once you leave service equipment everything supplied from said service equipment is feeders or branch circuits, never an additional service.
To make jumper happy I will make some code references, look in art 100 definitions at some of the words used here - especially service and feeder and a few definitions following 'service' that contain the word service and an additional word. Take a look at art 215 Feeders and 225 Outside Branch Circuits and Feeders. Also look in Art 250 for some of your grounding questions, pay particular attention to part III for grounding electrodes, and part VI and VII for equipment grounding.
After looking at those sections come back and ask any questions you still have. Most of what you are asking about will be covered in those sections.
