Greetings David,
Is it ok if I call you that my friend?
While I started to sit down and write a long response I figured this may answer your question more directly. When you read it and then have questions we can base additional opinions based on the context of the document below.
When to Select Solid Neutral Over Switched Neutral:
1. When to select a Solid Neutral: When the designer can incorporate the generator system into the rest of the
system, the generator set neutral is not grounded, and a transfer switch with solid neutral can be used. When
the neutral is common to the normal and standby systems, in the event of a fault, there could be some division
of current that would occur in the event of a ground fault. In this case, the 3-pole transfer switch must have
contacts designed to withstand fault currents for the period of time taken and required for the GFP device to trip.
2. When to Switch the Neutral: When the generator system is required to be separately grounded at site, a
transfer switch with a switchable neutral should be selected. With a switched neutral, the generator set can be
wired as a separately derived system to the load and normal power supply. In this configuration, the neutral
is not solidly connected through the transfer switch, but switched. Also, the neutral is designed to be switched
simultaneously with the switching of the load carrying phases. By utilizing this system, the designer/user will
ensure GFP operation as intended by NEC codes.
In the switched neutral mode, the generator is a separately derived system to the rest of the electrical system with
its neutral grounded at the housing. The neutral return path is left open for ground return currents by the transfer
switch contacts. In addition, nuisance tripping caused by unbalanced loads is avoided. The generator set is totally
separate to the utility supply and a safe alternative to a solid neutral connection.
Another example where a switched neutral connection is preferable is when there is more than one separately
derived electrical system being backed up by a common power source. An example of this would be a building
being fed by two different utility sources. For this type of installation, each utility service would have its own
separately derived neutral ground. To properly back-up portions of each utility service, the installation would require
two transfer switches. If the transfer switches had solid neutrals, each system would have two grounding paths. To
avoid this scenario, the designer would select a transfer switch with a switchable neutral pole to maintain the single
path to ground system.