If I have a separately derived system in my detached garage and I want to feed another building on the same property, do I need to carry the grounding conductor to the building being fed? Or can I just run the grounded conductor and the ungrounded conductors to the building like we are permitted to do 250.32(B)(2)

I think, with no metalic paths you can use 3 wires.

Greg- Now that I've baited you, let's take it a step further. There are no metallic paths between the detached garage and the other building. the other building is the house. The 3 wire supply from my SDS are two phase conductors and a common conductor. this 3 wire supply is feeding one side of a DPDT center off switch and the other side of the switch is the utility supply. The load for this switch is an emergency panel. Are you still okay with this hook up? The SDS, by the way has it's own grounding electrode (two rods) and GEC at the detached garage.

Make that a 3PDT and you are in business

Why 3 Pole? We don't have to break the neutral when we feed a building as per 250.32(B)92). and we will need a grounding electrode per the same reference AND if we don't break the neutral but instead go to the neutral buss we will have a grounding electrode.

George Little posted 02-14-2005 10:05 PM Let me ask if I'm following you on this. Since you have already installed a grounding electrode system for the derived system at the garage, you already have one at the house for the utility service, are you hoping to avoid needing one for the required building disconnecting means? If the transfer equipment at the house is suitable for use as service equipment and located nearest the point of entry of the derived system conductors it fulfills the requirement for a building disconnecting means. I do not believe that it is proper to use the neutral of the utility supplied feeder to the emergency panel as a grounding electrode conductor for the building disconnecting means. Once you install a grounding electrode conductor for the building disconnecting means you have to break the neutral because it would be grounded on the load side of the service disconnecting means during utility operation in violation of

250.24 Grounding Service-Supplied Alternating-Current Systems.
(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).
(5) Load-Side Grounding Connections. A grounding connection shall not be made to any except as otherwise permitted in this article.

So I agree with gfretwell that you would need a three pole switch for the transfer switch in this case. As long as that derived system neutral is bonded to the generator frame and to ground it is grounding connection to the grounded circuit conductor on the load side of the service disconnecting means during utility operation.
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Tom H

Tom, you and Greg are appearently 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 hazzard with feeding the Service rated transfer switch with three wires from a SDS. It's in my own house

I am actually reconsidering my answer. Without a metallic path the only thing I see you doing is scaring worms and we do that between the pole and the house all the time.
Two poles may do it.

This is like the guy who asked me why SPDT snap switches couldn't be transfer equipment.

Not sure why it isn't OK.

George Little Member posted 02-15-2005 09:21 PM
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.
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Tom H

Tom- Very briefly- The trransfer switch is Service Rated- It is the disconnect for the "feeder" from the other building- There is no EGC with the feeder so there is no paralleling of the neutral. the Grounding electrode for the utility and the "feeder" are one and the same in the house. The only question I have is-Since I don't need an EGC run with my feeder to a detached building when I come off the Service - Do I need one if I run from my detached building to my house off my generator. If I do then youare correct.

George Little Member posted 02-16-2005 04:06 PM George
No matter how many wires you use in the derived system's supply conductors to the house you still have to avoid re grounding the service supplied feeder neutral that runs from the Service Equipment to the Emergency Panel in the house. There are two ways to avoid this. One is to use a three pole switch so that the required grounding electrode conductor to your building disconnecting means; in this case the transfer switch; is not bonded to the service supplied feeder's neutral. The other would be to not bond the derived system neutral to the building disconnecting means. Remedy two is not available to you because you ran only three conductors from your derived system. You have to bond the derived system neutral to ground at the house as required in 250.32 (B) (2). If the generator does not supply any load, including any receptacles on the generator itself, at the garage then you can argue that 250.32 does not apply. You can also argue that it does not apply because the generator is not a service. But if you look at how transformers located outdoors are treated by 250.24 Grounding Service-Supplied Alternating-Current Systems, (A) System Grounding, (2) Outdoor Transformer, you will see that the intent of the code is to bond the neutral of the supply to buildings both at the outdoor source and at the disconnecting means. I guess my point is that if you are going to apply the rules for two or more buildings... to a derived system then you should apply them consistently.
--
Tom H

George
Is there actually no electrical supply to the detached garage from the service in the house? If there is any supply to the garage from the houses service then the derived system conductors are a metallic pathway in parrallel with that branch circuit or feeder and the branch circuit or feeder is a metallic pathway between the two buildings for the purpose of the wiring of the derived system.
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Tom H

Bingo! You are 100% on target Tom. Which goes to show that the inspector (me) is not always correct. This was a point that I had not considered. Thanks for your input and others on this page.

Changing the rules now huh?
You originally said no metallic paths. ;-)

Yah, got to do something sometimes to see if you are paying attention.

I assumed this was a "test" question.
If the generator is the sole source of power to the shed and serves loads there, the house is the second building.