Corner Ground Delta

[electrofelon]

Interesting, show me a normal three phase wye power disconnect (with overcurrent device ) where the neutral ( grounded conductor )is switched with the ungrounded conductors. Show me a split phase ungrounded conductor (neutral) that in a normal situation is switched with the ungrounded conductors overcurrent device.

Thinking about it more, I realized that I do not understand your position. You point out that there are very few general applications where the neutral of a wye or split phase circuit is switched and/or has an over current device in it. I am not sure if you are making a point about something and what that has to do with the issue of switching or having an OCPD in a corner grounded grounded conductor.

 

[pipe_bender]

Thinking about it more, I realized that I do not understand your position. You point out that there are very few general applications where the neutral of a wye or split phase circuit is switched and/or has an over current device in it. I am not sure if you are making a point about something and what that has to do with the issue of switching or having an OCPD in a corner grounded grounded conductor.

I am stating the obvious but I did not see this mentioned earlier in a wye or split phase system if you open the neutral and not the other phases bad things will happen as your L-N voltages will be all over the place, if you have a corner grounded system and just open the grounded phase the other two phases will keep running normally, a 3-phase motor might even continue to run.

Arc Flash calculations are based on 3-phase Line-Line-Line bolted faults.
The presence or absence of a neutral does not come into the equation.

Are you saying for any given size transformer bank with three equal kVA transformers, say three 100kVA pole mount, the Incident energy contribution would be the same in a 480V corner grounded delta as a conventional 480/277 wye?.
Would all the required PPE / approach boundaries be the same?

 

[jim dungar]

Are you saying for any given size transformer bank with three equal kVA transformers, say three 100kVA pole mount, the Incident energy contribution would be the same in a 480V corner grounded delta as a conventional 480/277 wye?.
Would all the required PPE / approach boundaries be the same?

Yes.

The presence or absence of a neutral impacts the probability of a 3-phase fault occurring. Quite commonly a L-N arcing fault will be cleared before it escalates into a 3-phase fault.

 

[Rjryan]

Done all the time for gas pumps. It's required by code.

Done all the time for gas pumps. It's required by code.

Gas pumps are in the section of the NEC labeled “ Special Occupancies”

 

[roger]

Where was Chapter 5 excluded from the conversation?

 

[Rjryan]

Where was Chapter 5 excluded from the conversation?

Where was Chapter 5 excluded from the conversation?

Interesting, show me a normal three phase wye power disconnect (with overcurrent device ) where the neutral ( grounded conductor )is switched with the ungrounded conductors. Show me a split phase ungrounded conductor (neutral) that in a normal situation is switched with the ungrounded conductors overcurrent device.
I would consider "Special Occupancies" that a special situation and not normal.
NEC 2023 240.22 (1) allows the grounded conduct to be switched, basically if the grounded conductor is open simultaneously with the ungrounded conductors. It could be done in every scenario but in a normal situation it is not, in special situations it is done.

• Grounding method: In a corner-grounded delta system, one of the phase conductors is intentionally grounded. This grounded phase essentially serves a similar function to a neutral in that it provides a path to ground. However, it is fundamentally a phase conductor, not a dedicated neutral conductor derived from a center tap or wye connection.
• While this grounded conductor is connected to ground, it is still considered a phase conductor and carries current under normal operating conditions. A neutral, on the other hand, is specifically designed as a return path for unbalanced loads and is typically grounded at the source.

 

[roger]

I would consider "Special Occupancies" that a special situation and not normal.

So you think a Mobile Home is something out of the ordinary? Mobile homes are in chapter 5 as well as Temporary Installations, there is nothing out of the ordinary if the installer does it all the time. Corner Grounded Deltas are nothing to be scared of.

 

[jim dungar]

This grounded phase essentially serves a similar function to a neutral in that it provides a path to ground.

Neutrals do not provide a path to ground. The NEC does not consider ground to be a normal current path. The ground bonding is actually to provide a path  from ground so fault current can return to its source.

 

[tortuga]

Its fun to consider the pros and cons of these rare and seldom seen systems, but just because a system is rare or seldom used does not mean it is more dangerous or should be prohibited.

A neutral, on the other hand, is specifically designed as a return path for unbalanced loads and is typically grounded at the source.

If you consider the neutral of a 5-wire two phase system it carries a current of something like %140 of the phase conductors.
also as Joe mentioned a neutral from a open wye 120/208 'single phase' feeder or service derived from a 3-phase system can see 100% neutral current if both phases are equally loaded with 120V loads.
Since a two phase system can be used to balance two single phase feeders perfectly on a 3-phase primary with two transformers I have actually seen more real life two phase systems than corner grounded, (but not powering any 4-wire two phase motors).

 

[electrofelon]

• Grounding method: In a corner-grounded delta system, one of the phase conductors is intentionally grounded. This grounded phase essentially serves a similar function to a neutral in that it provides a path to ground. However, it is fundamentally a phase conductor, not a dedicated neutral conductor derived from a center tap or wye connection.
• While this grounded conductor is connected to ground, it is still considered a phase conductor and carries current under normal operating conditions. A neutral, on the other hand, is specifically designed as a return path for unbalanced loads and is typically grounded at the source.

We could argue about what a "phase conductor" is (and have extensively in the past!). But for the purpose of the discussion, that classification is irrelevant. Can you provide some reasons why you think disconnecting the grounded conductor on a corner grounded system is prudent (if that is what your thesis is which I think it is)? Other than just saying because it's " fundamentally a phase conductor"? Also I will not except "because it's usually done that way" as a valid answer

 

[Rjryan]

This the best I can find for switching the grounded conductor in a grounded delta system is: “ The core principle is that if you’re going to disconnect power to a circuit, you want to ensure that all the conductors carrying current, both phase conductors and the grounded conductor, are interrupted. -Ensuring Complete Isolation.” The best I could find from the internet. Could not find an exact NEC code article dealing with this, but it makes sense from a safety standpoint. If someone has an NEC reference please come forward with the exact code.This the best example I can find for safely handling corner grounded delta. I'am done if you don't want to disconnect the grounded conductor or not it's up to you. I cannot find anything other than this that makes you or suggests you disconnect the grounded conductor in a corner grounded delta system.

 

[jim dungar]

Could not find an exact NEC code article dealing with this, but it makes sense from a safety standpoint. If someone has an NEC reference

There is no NEC reference, except for motor running overcurrent protection, but even then there is no requirement to open all 3 conductors.

See my post #64 for some reasons 3 pole switching is used with motors.

 

[hillbilly1]

So about 1990. That wasn't long ago

This is still a late model truck

View attachment 2579044

And anyone born after 1979 is a kid

The first gas pumps I done were for a Georgia Power truck yard, and that was around 83? The panel had breakers that also broke the neutral through an auxiliary contact. First time I ever seen that. Square D if I remember correctly.

 

[tortuga]

Done all the time for gas pumps. It's required by code.

It’s been code for more than 35 years, maybe 40.

So about 1990. That wasn't long ago

I love a history question dusting off the old code books it looks like that first appears in the 1947 NEC, so about 78 years ago or around the time Southern California Edison crews used that WWII work ethic to switch over So Cal from 50Hz to 60HZ including rebuilding hundreds of thousands of clocks and refrigerators on their dime.
1947 NEC section is 5141(e):
"All circuits supplying dispensing pumps shall be controlled by a switch having a disconnecting pole in each conductor".
In those days filling stations were located at 'repair garages' and did not require their own code article.
Prior to 1947 there may also have had a more general requirement under class I hazardous locations.

 

[roger]

This the best I can find for switching the grounded conductor in a grounded delta system is: “ The core principle is that if you’re going to disconnect power to a circuit, you want to ensure that all the conductors carrying current, both phase conductors and the grounded conductor, are interrupted. -Ensuring Complete Isolation.” The best I could find from the internet. Could not find an exact NEC code article dealing with this, but it makes sense from a safety standpoint. If someone has an NEC reference please come forward with the exact code.View attachment 2579077This the best example I can find for safely handling corner grounded delta. I'am done if you don't want to disconnect the grounded conductor or not it's up to you. I cannot find anything other than this that makes you or suggests you disconnect the grounded conductor in a corner grounded delta system.

So how many times are you going to repeat your posts?

 

[kwired]

This the best I can find for switching the grounded conductor in a grounded delta system is: “ The core principle is that if you’re going to disconnect power to a circuit, you want to ensure that all the conductors carrying current

Yet the majority of circuits you encounter with a grounded neutral all land the neutral on the neutral bus of the source panel and it is never disconnected when you simply turn the branch device off. Nothing prohibits opening that conductor, but must be opened simultaneously with the ungrounded conductors when you do so.

 

[Joethemechanic]

"All circuits supplying dispensing pumps shall be controlled by a switch having a disconnecting pole in each conductor".
In those days filling stations were located at 'repair garages' and did not require their own code article.
Prior to 1947 there may also have had a more general requirement under class I hazardous locations.

Yeah both my grandfather and my uncle had Esso stations at their garages. My grandfather's was built in the late 40's and my uncles was built in the late 30's. The last time I worked on a gas pump was one of those. In the early 80's we had to replace the tanks at my uncle's ESSO and when we excavated the front lot we found the original tanks. At best they might have been 500 gallons lol. My uncle's was a converted house that was maybe 1920's and still had K&T in the back rooms and upstairs.

 

[Rjryan]

I apologize, there are three ways to go if I understand MIke's YouTube videos on corner grounded delta systems: 1. If you want to switch the neutral you use a three pole breaker 2. Use a two pole breaker and run the grounded conductor straight through 3. Use a two pole fused disconnect run the grounded conductor straight through.

 

[jim dungar]

I apologize, there are three ways to go if I understand MIke's YouTube videos on corner grounded delta systems: 1. If you want to switch the neutral you use a three pole breaker 2. Use a two pole breaker and run the grounded conductor straight through 3. Use a two pole fused disconnect run the grounded conductor straight through.

Don't forget a 3 pole fused switch with an actual "dummy fuse" installed in the grounded phase. Just not a field fabricated one.

 

[ptonsparky]

Don't forget a 3 pole fused switch with an actual "dummy fuse" installed in the grounded phase. Just not a field fabricated one.

I've got several!!! Who wants one?