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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.

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

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

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

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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.