Corner Ground Delta

[jim dungar]

While that is what the code requires, I have never seen the grounded conductor of a corner grounded system actually identified that way in the field.

How long has this been required. I want to say it's only been 20ish years.

 

[don_resqcapt19]

How long has this been required. I want to say it's only been 20ish years.

It has always been required. As soon as you call it a grounded conductor, Article 200 applies.
It seems that most industrials did not think that Article 200 applied in the past.

 

[ptonsparky]

The one new system I did has been at least 40 years.

 

[jim dungar]

It seems that most industrials did not think that Article 200 applied in the past.

For sure that was the philosophy up here, unless it was new construction.
The old thought was the NEC did not apply to production processes, which slowly morphed into including the break locker rooms as well as offices.

Some 30 years ago, the state state started to say just because a local permit was not required for production process did not mean the NEC was optional.

 

[Joethemechanic]

There is no now nor will there ever be a reason to rely on wire color to determine the function and or voltage of that conductor.

I've never trusted colors, there was always the chance of them being wrong especially in old industrial installations just because of how many different fingers had been into them, and now with all the foreign made industrial equipment, things are even worse

 

[kwired]

Stop at my projects in NE.
Might be hard to find. Only had two at 480 and one of them has been torn out. IDR of any at 240 now.

I don't think I have ever seen 240 volt corner grounded from a utility company. I do remember once having a 240 ungrounded delta system for a specific piece of equipment, but it was separately derived within the facility.

480 was popular on farms up until into the 1990's though some still remain that were originally corner grounded, but all new services were typically 480/277 wye or an open delta but with a high leg. 480 volts is problematic enough with non qualified people working on them which can be common on farms, but having a grounded phase conductor just makes things worse for those that don't know what they are dealing with.

I remember long time ago we had a farmer that kept blowing fuse on the utility pole disconnect for his irrigation service. He decided to move that slug in the center pole to the position where the fuse kept blowing thinking it might resolve his problems. He ended up with a fire at the top of the pole from what he told us and moved the fuse back before calling the POCO of course.

 

[jaggedben]

I guess on a wye or delta what is the centertaps voltage if not bonded to ground I suppose i was under the impression that the centertap carrys 0 potiential but maybe im wrong

Yes you are wrong. If a grounded conductor loses the connection to ground then the voltage between that conductor and ground should no longer be assumed to be zero. This is essentially as true in corner grounded systems as other grounded systems.

BTW potential is always between two points. There is no such thing as a point having zero potential without reference to another point, which is why I don't like that phrasing. Perhaps that phrasing is partly at fault for misinforming you.

 

[Rjryan]

Sometimes images of a corner grounded delta system help.
The biggest problem with the corner grounded delta is recognized you are dealing with this system.

 

[WD40]

I have been told to use orange, yellow, blue for corner ground in the past.
Blue is the grounded phase.
White or gray should be reserved a wye system.

 

[zbang]

White or gray should be reserved a wye system.

But it's not, nor should it be. Blue could also be used for any "hot" conductor, so using it for the grounded one would be more confusing.

Basically, you were told wrong, see 200.6 and .7(A).

 

[electrofelon]

Right, just use white. Seems many people are irrationally uncomfortable with this. I've encountered a few corner grounded SDS's and they are always not white or "kinda" white (like a phase color with a few wraps of white tape.

 

[jim dungar]

Right, just use white. Seems many people are irrationally uncomfortable with this. I've encountered a few corner grounded SDS's and they are always not white or "kinda" white (like a phase color with a few wraps of white tape.

I think some of this is the basic electrical theory classes to focus on the neutral as the common refence for their examples and calculations. Maybe it would help if 'grounded conductor' was used more often.

 

[tortuga]

I only have seen a few and they just used standard phase colors and even ran the phase thru a 3-pole breaker, I am not sure why the push for wye but the utilitys and automation engineers both seem to prefer the conversion to a wye. The last corner ground I knew of was converted to a wye for free by the utility.

 

[ptonsparky]

I only have seen a few and they just used standard phase colors and even ran the phase thru a 3-pole breaker, I am not sure why the push for wye but the utilitys and automation engineers both seem to prefer the conversion to a wye. The last corner ground I knew of was converted to a wye for free by the utility.

They would convert, but then you had to get that 4th conductor in, somewhere, some how.

 

[Rjryan]

I have been told to use orange, yellow, blue for corner ground in the past.
Blue is the grounded phase.
White or gray should be reserved a wye system.

NEC 2023 200.6(A) Means of Identifying Grounded Conductors (1) Continuous white outer finish (2) continuous gray outer finish
There are a couple of other variations, but white and gray basically.

Ungrounded Conductors of a corner grounded delta system can be any color other than white, gray or green. typically:
White (grounded conductor) Red and Black ( ungrounded conductor).

 

[tortuga]

They would convert, but then you had to get that 4th conductor in, somewhere, some how.

Yeah it ends at the service disconnect.

 

[kwired]

The biggest problem with the corner grounded delta is recognized you are dealing with this system.

Biggest problem is some don't realize you can ground any conductor of a system and it then that conductor is at ground potential.

NEC as a general rule requires the neutral (when there is a neutral) to be the conductor that is grounded. When there is not a neutral that is when some people get confused on why/how you can ground a "phase conductor".

 

[ptonsparky]

I looked at a generator instal that had odd voltages when the competitors electricians were ready to test run it. Customer asked me to look. They had grounded the wrong lead. Fortunately they checked voltages before applying the load.

 

[pipe_bender]

While that is what the code requires, I have never seen the grounded conductor of a corner grounded system actually identified that way in the field.

Same here, I worked on very old mill building with a corner grounded 480.
The only thing fed out of the main switch-gear was the three elevators and two other new transformers (208 & 480 y), I always asked why it was originally used as everything else in the building was fed from the 480y277 or 208y120 transformer nobody ever had an answer. Anyone know the history on why you'd need one?

 

[ptonsparky]

Same here, I worked on very old mill building with a corner grounded 480.
The only thing fed out of the main switch-gear was the three elevators and two other new transformers (208 & 480 y), I always asked why it was originally used as everything else in the building was fed from the 480y277 or 208y120 transformer nobody ever had an answer. Anyone know the history on why you'd need one?

It was old. Maybe cheaper back when.