Over the years I have seen corner grounded, three phase, three wire systems. These are usually small 200 amp or less 480 volt services for sewer lift stations and the like. The Code requires white for the grounded conductor. I have seen many variations on this requirement. What color or colors have you seen or been required to use for this kind of a service ? I would appreciate your input.
Alan- I would argue that the conductor used for corner grounding is not a "grounded conductor" in the sense that it is used for a feeder or branch circuit but instead it is used to connect the system to a grounding electrode so it would not have to be white or grey. The few corner grounded systems I've seen are connected to the grounding electrode with a conductor identified with green tape. If I'm wrong, I need to be corrected. When you install a GEC to an electrode on a mid-point grounded system you are not required to have the GEC white.
I might add that I would prefer that they use either uninsulated or green and stay away from white so there is no confusing it with a "neutral" "grounded" conductor. Because you are correct grounded conductors conductors are required to be white or grey per Article 200.
Last edited by George Little; 07/18/1003:38 PM. Reason: Added thought.
That's a pretty clever question, Alan ... did you once like to annoy the local priest with impossible questions, when you were a kid?
I have yet to see such a conductor coded either as a 'neutral' or a 'ground.'
Indeed, the code is written so as to make it most likely a violation were the wire to be coded green.
Since it's a corner ground, this differs from the usual center-ground on a delta system in that it is essential to determining rotation of a three-phase motor. There is no 'single phase' created when this ground is used. It's very much a phase conductor, and thus cannot be marked white or grey either.
As a phase conductor, it is required to be disconnected at disconnects. As such, it cannot be bare. As such, you are allowed to fuse it.
So, I'd either leave it un-identified, or mark it a phase color. I have no opinion as to where it should be located in sequence at the lugs. One thing that is absolutely, positively clear is that you do NOT bond it to either the panel, or any 'neutral' busses that may be present.
I'm stuck with saying it's a "Grounding" conductor. It is used to ground the system. It is a Grounding Electrode Conductor. It is not a grounded conductor as discussed in Article 200. I guess that's why we have this forum to resolve these issues ha ha ha. We are not talking about any branch circuits, or feeders or Service Entrance Conductors we are talking about the GEC and I say it could be bare if that's what you choose.
The confusion starts with the fact that it is both grounded and grounding. On smaller services it is not unusual to have a non fused disconnect (480V) [for the utility] ahead of a standard meter socket and then the Service disconnect. The grounded leg IS BONDED to all enclosers ahead of the service disconnect as required by the NESC. It is then bonded at the service disconnect, per the NEC. The service disconnect could be two pole even though it is a three phase system. Connections to the ground rod etc. is done ONLY from the service disconnect. No additional bond wire is required between the utility disconnect, the meter socket and the service disconnect because the grounded leg is doing all those bonds. If that wire is insulated what color should it be ?
Alan, It is no more a grounding conductor than is the grounded conductor in a single phase 120/240 volt system. As far as a grounding function, again it is exactly the same as the single phase 120/240 volt system. The grounded conductor is used for both functions on the line side of the service disconnect. As to your question about the color of this conductor, it must be identified per Article 200.
The circuit to the equipment served by the corner grounded system needs to have two ungrounded conductors, one grounded conductor (identified per Article 200) and an equipment grounding conductor.
That being said, it is rare to find a corner grounded system with the grounded conductor correctly identified.
I'm sorry, but I have to differ, regardless of the 'plain meaning' of the words.
If you're talking about the part of the wire that goes from the service to the ground rod, I understand considering it as a 'grounding electrode conductor.' In that case, it can't be green or white, but it can be bare.
Yet, the wire doesn't stop there. It also goes from the transformer through the controls, and to the motors as a phase conductor. It simply can't be bare, green, or white; nor can it ever be bonded to the case. It is, in every meaning of the term, a 'hot' wire.
How can a wire be 'hot' and 'grounded' at the same time? Well, that little contradiction usually puzzles everyone the first time they run across it. IMO, it's one of those 'clever engineer tricks' that should never have been allowed, and it's long past time for them to be converted to a proper 3-transformer wye system.
I think we are all a little bit right and a little bit wrong. I just dug out the 8th edition of Soares and looked up Grounding Electrical Systems and got a crash course on corner grounded systems. If you have a copy look it up and check the text and the graphics. I was incorrect about the conductor color on the grounded conductor but my excuse is I thought Alan was talking about the GEC. Oops, I guess we can still learn and take a refresher course sometimes. Also note that the bonding screw is installed and the "white" grounded conductor goes to the what we traditionally call the bar. Thanks for the help Don.
George, Not only does the white conductor go to the "bar', in some cases the listing permits you to use standard single phase panels for this type of 3 phase system. A substantial cost reduction over the use of 3 phase panels.