George Little Member posted 02-15-2005 09:21 PM
Tom, you and Greg are apparently subscribing to the concern that
we are grounding the neutral twice if we don't use a 3 pole switch. We
do it all the time when we feed a detached building with two hots and a
neutral (no EGC) and then establish a grounding electrode system in the
detached building and fasten the neutral to it. I will be attending the
Soares grounding seminar put on by IAEI in about 3 weeks and I will
bounce this off the speaker. In the mean time I don't see a hazard with
feeding the Service rated transfer switch with three wires from a SDS.
It's in my own house.
George
Your missing my point I think. Looking at your house alone and
considering just the neutral of the feeder to your emergency panel, It
would end up grounded at the Transfer Switch which is on the load side of the Service Disconnecting Means. This would still be true even if the
Generator were right at the house just outside in a weather proof
enclosure and the Generator's breaker were serving as the Building
Disconnecting Means. There are two ways to wire a permanent generator's
neutral under the separately derived system rules. You can bond the
neutral to the frame or at the first disconnecting means or you can
isolate it from ground if it is solidly connected to the service
neutral. What you cannot do is to bond it at the generator and leave it
solidly connected to the service neutral unless the transfer switch is
also the service disconnecting means. In your case the transfer switch
is on the load side of the Service Disconnecting Means.
Since your generator is in another building the conductors from it to your home are Outside Feeder or Branch Circuit conductors. A Building Disconnecting Means is required. With a three wire feeder the neutral must be bonded at the building disconnecting means. With a two pole transfer switch; or another two pole Building Disconnecting Means; that grounding connection would be on the feeder neutral as well. That means that you have a grounding connection on the load side of the Service Disconnecting Means of your homes wiring system. The problem is not with the grounding at the garage but rather the grounding of the neutral of the feeder that supplies the utility power to the emergency panel inside your home. With that arrangement the Equipment Grounding Conductor of the feeder is in parallel with the feeder neutral.
That is one of the reasons that I will wire an emergency panel as a
service supplied panel when that is practical. When the Service
Disconnecting Means is located in the cabinet with the Panel all of the
supply grounding connections are on the line side of the Service
Disconnecting Means. Another good way to avoid this hassle is to use a
transfer switch that is "Suitable for Use as Service Disconnecting Means" as the service disconnecting means.
I hope that was clearer so that you can see that my concern is with the feeder neutral being inappropriately grounded rather than with the number of conductors in the outdoor feeder.
--
Tom H
