For a system can be supplied either strictly from a utility source or strictly from a generator, the 2014 NEC code specifically addresses where to ground the generator neutral based on using either a 3 pole transfer switch or a 4 pole transfer switch. However, each of these scenarios appear to assume that there are neutral loads and therefore, a neutral will be ran from both the utility service entrance equipment to the transfer switch and from the generator to the transfer switch. If a 3 pole transfer switch is used, the generator neutral is not grounded at the generator but is ran to the transfer switch where it is solidly connected to the neutral from the utility service entrance equipment (i.e a non-separately derived system). If a 4 pole transfer switch is used, the generator neutral is grounded at the generator and both the generator neutral and the utility service neutral are connected to the 4th pole of the transfer switch where they are switched (i.e. a separately derived system). However, where in the code does it address what to do when there are no neutral loads and therefore, there is no need for the utility neutral to continue beyond the service entrance equipment or for the generator neutral to extend beyond the generator? The code seems to imply that there must be a neutral wire between the generator and the utility service entrance equipment, but I can't find where it specifically states this. If you have a 4 pole transfer switch and you ground the generator neutral at the generator, this appears to be the definition of a separately derived system. However, in this situation, if you do not run a neutral from the utility service to the 4 pole transfer switch or from the generator to the 4 pole transfer switch, is this a code violation? If this is not a code violation, would it become a code violation if you replaced the 4 pole transfer switch with a 3 pole transfer switch under this situation (i.e. no neutral loads - therefore, no neutral from the generator or the utility service entrance equipment)? In each of these situations, please assume ground fault protection/indication has been addressed when operating solely off the utility and solely off generator.
Thanks, Chris D.