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.

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.

There is no question that this conductor is a grounded conductor and must be identified per the rules found in Article 200.

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.

This conductor is not both "hot" and "grounded" at the same time. It is a grounded circuit conductor and no different from the grounded circuit conductor in a 120/240 single phase system.

Well, that's exactly where we differ.

The grounded leg of a corner grounded delta simply cannot be the 'same' as the grounded conductor of a center-tap delta. At the risk of repeating myself, I'll try to illustrate the difference with a few examples.

If you have a 3-phase motor on a center-tap system, the grounded conductor does not come into the picture at all. The motor will operate exactly the same whether the "neutral" is there, or not.

By way of contrast, that same motor on a corner grounded system absolutely needs to have that 'grounded' leg in order to operate. Swapping leads will change the directoin of rotation - something that doesn't work with single phase motors.

Then there's the fine matter of meter readings. Measure between any two legs, and you'll get full voltage - even though one of those legs will show "0" volts to ground.

These variations are probably why code language has been so turgid when it comes to discussing the 'neutral.'

Don is right, this will look exactly like a 120/240 circuit, two ungrounded conductors (any color) and a white wire plus the bare/green EGC. The switch gear will look a lot like single phase but it still needs a
delta" listing.
Jim Pauley had a great pitch on this and I was paying attention because the state did a bunch of corner ground sewer pumps.
It scares a lot of people but it is a very elegant way to serve 3 phase loads if you don't need a neutral.

It is the same as far as how we use it and how we identify it. It is a grounded circuit conductor. It is not a neutral. All too often the term grounded conductor and neutral are used interchangeably and that is not correct.
Both the corner grounded system and the 120/240 volt single phase systems have two ungrounded circuit conductors and one grounded circuit conductor. There is, of course, a difference in the voltage readings between the grounded and ungrounded conductors of the two systems, and one system is single phase and the other is three phase.

Read Soares Grounding Book. Theres Color pics ect. Explains Everything very clearly. Showing the Correct color codeing of the Grounded conductor.

Hello all, please pardon the latency of this reply (I just came across the post this evening - 07-23-2010).

I have dealt with many Corner Grounded Delta Systems - with apx. 50% of them being 240V, 40% being 480V, and the remaining 10% being "Various Flavors" (220V, 380V, 600V).

The Line (or Phase - which ever you choose to call it) that is intentionally _GROUNDED_ (Bonded to the GES), is simply the System's Grounded Conductor; and should be treated as all other System Grounded Conductors per NEC Article 250:

• "The System Identified Conductor" White or Gray Color,
• No OCPD in Series - except Multipole Circuit Breakers,
• No Fuseing at Safety Switches / Disconnects (Solid Link in place of Fuse),
• Ground Bonding at the Service / SDS only (unless there are the typical exceptions).

Standard conformity places the Corner Grounded Line / Phase in the "B" Position; so Line "B" = Grounded Conductor.

In Motor Circuits, if there is an OL unit as the final OC device, the Grounded Conductor of this Delta may contain OLs.

Attached below are (3) different Drawings of Delta 3 Phase 3 Wire arrangements;

A: Center Tap Grounded,
B: Corner Grounded (Line "B" = Grounded Conductor),
and
C: Ungrounded.

........................................................
........................................................



Fig. 1A: 240V 3 Phase 3 Wire Center Tap Grounded Delta

......................................................
......................................................



Fig. 1B: 240V 3 Phase 3 Wire Corner Grounded "Phase B" Delta

......................................................
......................................................



Fig. 1C: 240V 3 Phase 3 Wire Ungrounded Delta

......................................................
......................................................

These are 240V Systems, but same remains if the System Voltage is 120V, 220V, 380V, 480V or 600V.

BTW, these Schematics are in the Technical Reference section.

Scott

El-Bump'o!!!

Anyone have comments to what has been posted so far?

Scott

I would just dd that the grounded corner should be white and you don't need to run it through the disconnecting or overcurrent device.

The last time I did the 240 volt corner grounded delta system I know the code do required to be white however I did change to grey to indentify a corner grounded and my inspector approved after I gave him a head up why in first place.

Otherwise what I do is put a band on it as well to warn anyone else that print is say " Corner grounded conductor " that will give them a head up.

Merci.
Marc

I started this because many are unaware that corner grounded systems are even being installed. The color coding came up because I have seen every varity of colors starting with the basic colors for three phase and then deciding which color to not use, i.e. 480 V brown, orange, yellow. Which color do you drop ? Do you use grey for the grounded and hope the next guy knows what he is looking at ? I would always do a simple line drawing of a delta with the ground off the corner inside the disconnect and trust that whoever had the equipment open would recognise it.
I had one utility guy insist on red with a wrap of green with the brown & yellow to flag it for line crews that might come into the area from other regions in case of major outages.
A good understanding of corner grounded systems is as important as an understanding of a 4 wire, high leg 3 phase. Not knowing can cause injury and damage to equipment.
I hope that some may have benefited from this post.

The first one I saw confused me for a minute but I did know there was such a thing as corner delta so I did figure it out. (and pretty proud of myself that I did it before I said something dumb) The colors they used were red, blue and white. Very patriotic and also a fairly good indicator for a 240v 3p corner system, The fact that one wasn't black was a tip off that it wasn't standard 120/240 and 2 transformers on the pole was another cue that you had 3p.
Fortunately there was a wiring diagram in the starter that confirmed this was really 3 phase but it did not say anything about the grounding.

I think if I was doing 480 corner I would use brown/yellow/gray, just because gray is the common grounded conductor color on 480 and orange can cause confusion. BOY is a common convention on 480 wye but when delta is involved it is supposed to be the high leg if this was center tapped. Omitting it alerts you something else is going on. Actually I have heard a lot of people who want BOY to go away because of the high leg thing. I think it is so ingrained in the culture that it is probably here to stay.

I agree; more of the Field Personnel should be aware of the Corner Grounded Delta Systems - as they still are used in Industrial areas... (not to mention awareness of all other System types, but that's another post!).

Even more importance falls on the SDS from a "Reverse Connected Delta / Wye Transformer", and a solid + correctly Grounded output.

Per Color Codes and System Identifications, on all the Projects I have dealt with, where a Corner Grounded Delta was involved (either an SDS, the Utility supplied System, or both), Designs and Installations were targeted to clarification of System usage + capabilities.

Service Section / Transformer contained explanation - via schematics - why there are only Three Conductors - One being White (or Gray), on this 3 phase System.

Safety Switches (Disconnects) contained descriptive Schematics and text, regarding why the "B Phase" has no Fuse; and instead has a Solid Link".

Corner Grounded Deltas Color Coding was similar to Greg's description:
A = Red, B = White, C = Blue.
Where there was an SDS Corner Grounded Delta, the Color Code became:
A = Brown, B = Gray, C = Yellow.

Side Note:
I performed Engineering & Design work on a recent Industrial Project, which has Two Service Sections (One is Single Phase 3 Wire, the other is 3 Phase 3 Wire - both fed from a Utility Owned 4 Wire Delta Transformer), and to include a new 480V Corner Grounded SDS for Large Motor Loads.

Most of the Field Personnel had no clue as to the "Odd-Ball Power Systems", as well as my specifications on the Plans, regarding the output of the new SDS Transformer... such as:
"Grounding Phase B",
"Color Code for Phase B = Gray",
and
"No Fuse in Phase B at Disconnects - Solid Links only".
(There is much more information on the Plans than what I show here)

This resulted in me supporting the Field Crews.
They had never seen - or heard of Systems like this; but with some explaining, they were able to grasp the basics.
There were still many puzzled looks, though!

Color coding on this Project ran as follows:

System #1. 120/240V Single Phase 3 Wire (from Service #1 "Lighting"):
Line "A" = Black,
Line "C" = Blue,
System Grounded Conductor = White.

System #2. 240V Three Phase 3 Wire (from Service #2 "Power"):
Phase "A" = Black,
Phase "B" = Orange (High Leg),
Phase "C" = Blue.

System #3. 480V Three Phase 3 Wire (from SDS Transformer):
Phase "A" = Brown,
Phase "B" = Gray (System's Grounded Conductor),
Phase "C" = Yellow.

All Panelboards, Disconnects, Service Sections, and the Transformer contained Color Code charts denoting all Three systems.

Any comments?

Scott

Were you the engineer on record for local planning & permits, requiring a Class "A" license in California, or was this an industrial-maintenance project?

A Class "A" license General Engineering License isn't the license that's required. (That's more for building highways, power generation plants, bridges, and the like).

Any licensed PE can stamp the plans,

or

Read California Business and Professions Code Section 6737.3, which states that any licensed C-10 electrical contractor can engineer a job, as long as the contractor is performing the work himself.

Yes, I see:
DEERING'S CALIFORNIA CODES ANNOTATED cites one case decision under this statute, known formerly as § 6737.4:
Wynner v. Buxton (1979, 2nd Dist) 97 CA3d 166, 158 Cal Rptr 587, 1979 Cal App LEXIS 2163.
No liability was found against a PE who stamped plans "omitting all mechanical and electrical details which may be supplied by mechanical or electrical contractor".

Also see: CA B&P § 6747 Exemption for Industries.
Except for civil engineering, the performance of unlicensed-engineering work is permitted for corporate consultants, temporary employees, contract employees, and those persons hired pursuant to third-party contracts (handymen).

Why bother using licensed contractors at all, when CA B&P § 6747, permits corporations to use unlicensed maintenance-electricians and handymen to engineer electrical systems?

PROFESSIONAL ENGINEERS ACT
(Business and Professions Code §§ 6700 – 6799)
http://www.pels.ca.gov/licensees/pe_act.pdf

Ramsy,

Yes I was the Person responsible for the Preparations of the Documents.
This was a Design / Build Project; Contractor's License classes are B & C-10.

We perform Design / Build services pursuant to California B&P Code, Division 3, Section 6737.3.
("B&P" = Business and Professions Code)

Scott