I have installed a lot of gensets at cell tower sights and on dairy/poultry farms, and never use a 3 pole switch. We run a neutral wire from the incoming service, one from the load, and one from the genset and hook them all together in the transfer switch(isolated from ground) and we pull equipment grounds in all conduits and connect them together and bond to ground. The neutral in the genset is NOT bonded to the ground. This arrangement has been inspected and passed with power companies and AHJs all over the southeast.
