If I backfeed a dwelling with a optional automatic stand-by power from a permanently installed outdoor generator set, do I need to hit a building disconnecting means before the automatic transfer equipment?
If the ATS will receive the service conductors before the house main disconnect, then the ATS must be service rated. Whether you need to hit a disco with the gen conductors before the ATS depends on where the set mounted CB is. Also see 225.31 If the generator neutral will be solidly grounded, then be sure that your transfer switch also switches the neutral (3 pole) as the bonding of the neutral indicates a separately derived service and requires the extra transfer of the neutral. Many ATS's have the indication required. The AHJ would have to say it was practical to install the annunciation, most don't.
Re: Outside Generator Set#50549 04/06/0507:13 AM04/06/0507:13 AM
#2: These conductors are not Article 225 circuits.
Now, for specific questions you asked:
You asked "If I backfeed a dwelling with a optional automatic stand-by power from a permanently installed outdoor generator set, do I need to hit a building disconnecting means before the automatic transfer equipment?" See Article 230.72. This allows you to have a remotely located disconnect (such as on the genset).
You asked "Is it necessary to install audible and visual signal devices as mentioned in 702.7 with a permanently installed outdoor generator set?" Your transfer switch should have these devices installed, so you probably won't have to worry about it.
You asked "The service conductors will hit the service disconnect before the ATS...is the ATS bonding allowed through the grounded conductor with this arrangement?" The answer would be no, since the service equipment would stop at the main disconeect. A seperate equipment grounding conductor would have to be run from the disco to the ATS, and all grounding electrode connections would be made in the disco. Another option would be to run both systems into the ATS, then to the disco, after the ATS. Then you would not have to run the EGC between the ATS & disco, as your grounded circuit conductor would suffice.
Ron was correct in his statement that the ATS needs to be service rated (if installed before the disco). His reference to Article 225 is incorrect, as this is a Article 230 issue. His statement about the switching of the neutral in the ATS is also incorrect, as this is not a seperately derived system (see definitions). The determining factor for a seperatly derived system is not that there is a solidly grounded conductor, but instead that there is NO interconnection.
So, with the grounding electrode system being within the building (metal water pipe), that is used for grounding the building service disconnecting means, and with the ATS having a solidly connected grounded conductor, I will not bond the grounded conductor of the outdoor generator set to its frame, and I will use the building grounding electrode as the electrode for the gen set...whew
I will also run a grounding conductor out to the gen set for grounding its frame...
Lastly, I also will place a sign at the grounding electrode identifying all soures of power...per 702.8(B)
Stallcups generator book is "in the mail" so I can understand this...
If the generator neutral is solidly interconnected to a service supplied system neutral (not switching the neutral in the transfer switch), then it is not a separately derived source. Then you don't bond the n-g at the gen. If on the other hand the n-g on the gen is bonded, you either unbind at the gen or switch the neutral in the transfer switch. See 250.20(D) FPN 1
Rick, I choose one, then make the other comply. If I believe that the gen will have a bond that I can't remove, then go with the switched neutral tran sw. If the trans sw is existing and doesn't switch the neut., then I make sure I can remove the bond in the gen.