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.