B Phase corner grounded delta

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rojay

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I apologize for the length of this post first of all. I have to preface my question by saying I do not have much experience dealing with corner grounded delta systems. Recently, I was asked to inspect some work that was done by another contractor and came across multiple issues that appear to my eyes to be code violations. On the rooftop of a 10 story building is a 200 amp 120/240 volt single phase panel fed from the secondary side of a single phase 37.5 kva transformer. Transformer has single phase 480 coming to the primary side. Inside the transformer disconnect switch (unfused 100 amp) are A and C phases with a green equipment ground that is landed to a ground lug inside the disconnect that ties the equipment ground from the line side supply to the load side feeding the transformer primary. So far, so good in my eyes. Where I ran into issues was the basement where the feeder originates. The feeder came from the service switchgear into a junction box where it ties into an Emon sub meter. All three phases were brought to the meter with an equipment ground. First I don't understand why all three phases were needed for a single phase application. B-phase was orange which I believe needs to be white or gray? The equipment ground was landed to a ground lug inside the splice box and a ground was provided for the Emon case. That's where the EG ended. The #2 green that I assumed was a EGC on the roof was spliced to the orange B phase wire inside the splice box. My thoughts on correcting this installation would be first to only bring phases A and C to the Emon along with an EGC. Emon would be wired only using 2 current sensors and the remaining pair of contacts inside would need to be jumped out. I don't have enough experience with corner grounded deltas or Emon meters to know if I'm on the right track here. Does anyone have any thoughts?
 
Are you sure the service is 3-phase 3-wire Corner Grounded, in which case "B" should be white or gray?
O,r is it a 3-phase 4-wire Delta with a Wild Leg, in which case "B" could be orange? 480/240V wild leg systems are not commonly found as services to multi-story buildings.

It is possible that the service entrance conductors are colored because they are ungrounded. The corner bonding probably occurs in the service entrance equipment, at which point the conductor was incorrectly changed to green.

Maybe you looking at the common point for in service where B-Phase, the Grounding Electrode Conductor, and the green grounding conductors might all be 'tied together'.
 
This is definitely a corner grounded delta to my untrained eyes anyway:) Feeder comes from fused disconnect switch in the switchgear with a link placed in B phase position that will not allow a fuse.
 
rojay said:
This is definitely a corner grounded delta to my untrained eyes anyway:) Feeder comes from fused disconnect switch in the switchgear with a link placed in B phase position that will not allow a fuse.
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Is the corner-grounding connection at the utility transformer or in the service entrance equipment?
Where is the Grounding Electrode Conductor terminated?
What color is the grounded conductor, when it is used in a 3-phase circuit? I think improper identification of a grounded conductor is the most common error I find with corner-grounded installations, especially older ones.
Where do the Equipment Grounding Conductors normally terminate?
Are there multiple phase-ground bonds in the system?
 
The corner grounding connection is in the switchgear. The EGC lands at the same bar that the grounded conductor does in the service switchgear. I haven't looked into any other circuits coming from the gear beside the feeder that is in question. B phase of my feeder is orange. I am questioning the need of even including B phase for the single phase feeder that is supplying the single phase rooftop transformer. I believe the fact that what I thought was an EGC in the transformer disconnect switch is spliced to the orange grounded conductor in the Emon splice box indicates that an improper phase- ground bond has been made. Phase to phase voltages are- A-B- 480 volts B-C - 480 volts. C-A- 480 volts along with 480 volts to ground for both A and C phase. B phase to ground is zero. I was contemplating just disconnecting the case bond that has been made in the disconnect switch since the feeder has been run in conduit it's entire length and letting it serve as the EGC
 
rojay said:
...I believe the fact that what I thought was an EGC in the transformer disconnect switch is spliced to the orange grounded conductor in the Emon splice box indicates that an improper phase- ground bond has been made....
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Sounds like it to me. The conductor should be identified per 200.6 which basically says it definitely shouldn't be orange or green.

And yes, it's improperly bonded if it's hitting grounded enclosures at any point past the service.

Since you have a proper EGC in your meter panel, what about just lifting the green conductor off of "B" phase and tying it to that EGC so it will then work as designed?
 
If the green conductor is removed from B phase and connected to the EGC in the splice box, what effect will that have on the Emon meter? Not really sure why all three legs were needed at the Emon to monitor a single phase setup anyway. At this time there is a current sensor wrapped around the green wire and reading it as a load wire, I guess. There are three wires spliced together at this junction- an orange feed from the gear, a second orange that feeds the Emon and the green B phase that goes up to the transformer disconnect.
 
The meter is probably designed to monitor three phases, possibly needs a voltage reference for all three phases but will still meter accurately if there is only current on two phases (conductor or no conductor in the third CT will not matter).

If meter needs a voltage reference then there should be a B phase conductor and a separate EGC supplying it. Of course if it is a grounded conductor that B phase conductor should be white or gray or at least identified with white/gray if it is larger then 6 AWG .
 
rojay said:
If the green conductor is removed from B phase and connected to the EGC in the splice box, what effect will that have on the Emon meter...?
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There should be zero load current on that conductor because it simply terminates at the disconnect enclosure, correct? So the CT isn't doing anything.

Right now there will likely be some current flowing on it because having the neutral bonded in multiple spots just creates a bunch of parallel paths for neutral current to flow over the grounded surfaces.

Be sure about the wiring, though. If this thing is being used as a neutral at some point along the line, opening it could damage something.
 
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big john said:
There should be zero load current on that conductor because it simply terminates at the disconnect enclosure, correct? So the CT isn't doing anything.

Right now there will likely be some current flowing on it because having the neutral bonded in multiple spots just creates a bunch of parallel paths for neutral current to flow over the grounded surfaces.

Be sure about the wiring, though. If this thing is being used as a neutral at some point along the line, opening it could damage something.
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You probably on right track here but need to clear up some technicalities. If this is a corner grounded delta there is no "neutral". There is a "grounded" conductor that gets treated just like the "grounded neutral" does in most other grounded systems though - it gets bonded at service equipment or source/first disconnecting means for other then service supplies, it remains separated from the EGC beyond the main/system bonding jumper to prevent parallel current from the "grounded" conductor from flowing through the EGC and other bonded objects.
 
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