Not necessarily. If I recall my NEC correctly, separately derived systems below 1000 amperes 3 phase can have a common neutral, or systems without a GFP on the service entrance breaker.
1000 amps and above with GFP on the service entrance breaker should use what is known as an "overlapping switched neutral", sometimes erroneously referred to as a "fourth pole" on the transfer switch. In these systems the neutrals are electrically separated from each other, that is, the neutral for the generator and the neutral for the distribution system are not connected to each other through something such as a neutral bar. The overlapping switched neutral in the transfer switch is just that - a pole that allows the neutrals from both systems to be connected together briefly, then opened (disconnected) from the source you are moving away from. Since the neutral is not a fully rated current carrying circuit under normal operation, this additions pole in the transfer switch is considerably smaller than the main contacts. The use of ground fault protection on the normal source distribution system can have nuisance trips occur if the neutral is grounded both at the normal service and the generator. Multiple neutral grounds would allow ground fault currents to be split between the two sources, effectively negating the function of a ground fault sensor. If the neutral of the generator is grounded as a separately derived system (I think that's NEC 250) you must disconnect the neutral from the utility from the neutral of the generator. I can look this stuff up if necessary, but just think of it as when you want the generator to appear as its own source, much like a utility, and you have GFPs in the mix and you're at or above 1000 amps service, you need to have an overlapping switched neutral in the transfer switch. Dan On Nov 5, 2012, at 4:51 AM, Hans Neureiter <diese...@gmail.com> wrote: > So a "properly installed transfer switch" also isolates the neutral line to > the grid? > > On Sun, Nov 4, 2012 at 10:30 AM, Peter Frederick <psf...@earthlink.net>wrote: > >> This is why one should have a properly installed transfer switch to use a >> generator for the house. That way whatever circuits you choose to power >> will be completely isolated from the main power grid while the generator is >> in use, and you won't electrocute a lineman nor try to run the entire >> neighborhood off a 5000 watt generator. >> >> Otherwise, use extension cords for specific appliances and don't use the >> house wiring at all. >> >> Peter >> >> >> ______________________________**_________ >> http://www.okiebenz.com >> For new and used parts go to www.okiebenz.com >> To search list archives >> http://www.okiebenz.com/**archive/<http://www.okiebenz.com/archive/> >> >> To Unsubscribe or change delivery options go to: >> http://mail.okiebenz.com/**mailman/listinfo/mercedes_**okiebenz.com<http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com> > > > > -- > Hans Neureiter, Katy, TX > '82 300SD > '01 VW New Beetle 1.9L TDI > _______________________________________ > http://www.okiebenz.com > For new and used parts go to www.okiebenz.com > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
