240 V three phase 3 wire corner grounded Delta

[zappy]

I've never dealt with a system like this out in the field. Any stories or advice about this kind of system would be greatly appreciated. Thank you for your help.

 

[LarryFine]

The only thing that makes a neutral the grounded conductor is that we intentionally ground it.

You have a delta with the C phase intentionally grounded, and the B phase accidentally grounded.

The fuse blew just as it would in any system with an intentionally-grounded conductor and a fault.

By the way, the grounded phase shouldn't actually be fused, while a 3p breaker would be allowed.

Have you a specific question?

 

[augie47]

The grounded phase would not normally have any overcurrent protection as you treat is an any grounded conductor.
The systems are somewhat rare in this area and there a lot of equipment does not play well with this type system especially when drives are involved.

 

[don_resqcapt19]

In general think of a 120/240 volt system....other than the voltage to ground, they work the same way.

Note, a fuse is not permitted in the grounded conductor unless it is being used a motor overload protection.

 

[TX+ MASTER#4544]

The corner grounded transformer has zero voltage, thus it's known as the ghost or "fhantom"(sic) voltage transformer.
You still have 240 V between conductors. It's a delta transformer. 250.24(D)(3)
It looks just like a normal service. Some disconnects may not have a fuse in that ghost leg.
Could be a strip of copper in lieu of a fuse. They are rare and seldom used.
So use caution if you encounter a corner grounded transformer and think maybe the utility company lost one of their phases.

Thanks for reading.
Comments accepted.
TX+MASTER#4544

 

[electrofelon]

The corner grounded transformer has zero voltage, thus it's known as the ghost or "fhantom"(sic) voltage transformer.

Not sure what you are trying to say here

 

[LarryFine]

Not sure what you are trying to say here

Methinks he meant the grounded conductor.

 

[tortuga]

Fun fact 240 corner grounded delta often used blue as the grounded phase, just like 416Y/240 systems use light blue as a neutral.
Blue never made it into the NEC as a permitted grounded conductor color other than flexible cords. Using blue as a neutral or grounded conductor requires 'special permission' from the AHJ.

 

[don_resqcapt19]

The corner grounded transformer has zero voltage, thus it's known as the ghost or "fhantom"(sic) voltage transformer.
You still have 240 V between conductors. It's a delta transformer. 250.24(D)(3)
It looks just like a normal service. Some disconnects may not have a fuse in that ghost leg.
Could be a strip of copper in lieu of a fuse. They are rare and seldom used.
So use caution if you encounter a corner grounded transformer and think maybe the utility company lost one of their phases.

Thanks for reading.
Comments accepted.
TX+MASTER#4544

Fuses are not permitted in the grounded conductor of this system, or any other system, other than the rare case where they are being used as motor overload protection.

It is not a ghost leg, it is a current carrying conductor of the system just like any other grounded conductor. It reads zero volts to ground, just like any other grounded conductor, other than any neutral to earth voltage on the system as a result of voltage drop on the

It also is required to be white or gray, again like any other grounded conductors.

 

[don_resqcapt19]

Fun fact 240 corner grounded delta often used blue as the grounded phase, just like 416Y/240 systems use light blue as a neutral.
Blue never made it into the NEC as a permitted grounded conductor color other than flexible cords. Using blue as a neutral or grounded conductor requires 'special permission' from the AHJ.

The code has always required the use of white or gray for that conductor, just like for any other grounded conductor. However, I have never seen white or gray used for this conductor in the field.

Not sure what reason there would be for the AHJ to issue a 90.4 written permission. I don't see any reason to permit another color to be used to identify this conductor. It is a permission I would never grant as I don't see another color as assuring that "equivalent objectives can be achieved by establishing and maintaining effective safety" as required for a 90.4 permission.

 

[zbang]

The code has always required the use of white or gray for that conductor

Sure, but out at the street, the PoCo will use what they want - services sometimes come in colored as red/white/blue with a bare (or black!) neutral.

 

[Hv&Lv]

Sure, but out at the street, the PoCo will use what they want - services sometimes come in colored as red/white/blue with a bare (or black!) neutral.

I have tried to get our guys out of the old red, white, blue habit.
But old habits die hard.
At least the young ones are picking up on using something else, mainly yellow, for the old white phase..

 

[don_resqcapt19]

Sure, but out at the street, the PoCo will use what they want - services sometimes come in colored as red/white/blue with a bare (or black!) neutral.

Yes, but the code starts at the service point and the grounded conductor on the load side of the service point must be identified in accordance with the rules found in Article 200. It does not make any difference that the utility used a different color on the line side of the service point.

 

[Electromatic]

To the OP: I find it helpful when dealing with unfamiliar systems to remember the basic fact that voltage is a potential between two points.
In your picture, B is faulted to ground and C is intentionally connected to ground. Therefore B, C, and ground --beyond the OCPD(fuse)-- are all the same point, so there is no voltage. If you took readings on the other side of the fuses, there would still be 240V between B and C and between B and ground (C & ground being the same point).

 

[tortuga]

However, I have never seen white or gray used for this conductor in the field.

Thats all I was pointing out that blue is typically the grounded conductor in a corner grounded.
I have never seen a corner grounded system supplied by a utility, only at a large facility that has a MV service and a whole list of systems.

 

[Hv&Lv]

Thats all I was pointing out that blue is typically the grounded conductor in a corner grounded.
I have never seen a corner grounded system supplied by a utility, only at a large facility that has a MV service and a whole list of systems.

We have about a dozen on our entire system. Do not build new ones. We end up on too many trouble calls where someone is calling saying one leg is out when they put a voltmeter on it.
Dispatchers don’t understand enough to explain it, so they roll a trouble truck.

 

[don_resqcapt19]

Thats all I was pointing out that blue is typically the grounded conductor in a corner grounded.
I have never seen a corner grounded system supplied by a utility, only at a large facility that has a MV service and a whole list of systems.

Have never seen it as blue...most often just black like the other phase conductors and typically marked with phase tape, often black, red, blue.

 

[tortuga]

typically marked with phase tape, often black, red, blue.

Thats weird they phase tape the grounded conductor black, red, blue?
I would think it would just be blue phase tape for the grounded C phase.

 

[don_resqcapt19]

Thats weird they phase tape the grounded conductor black, red, blue?
I would think it would just be blue phase tape.

sorry, I tried to say black, red, blue, one for each phase, the common low voltage phase conductors.

 

[tortuga]

sorry, I tried to say black, red, blue, one for each phase, the common low voltage phase conductors.

I am just messing with you I think we were saying the same thing the grounded phase was usually marked blue in one way or another.