PHASE-TO-GROUND NO VOLTAGE (I'M NEW TO THE INDUSTRY)

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Hi to all!

I'm new to the industry (recently obtained my engineering license) and started as a project engineer. And as a project engineer, I have to make sure electrical projects are completed on time. But there is a hiccup in our project as we were to supply temporary power from a tenant panel to another panel, we had a grounded phase.

Basically, we have correct phase-to-phase, phase A-to-ground, and phase C-to-ground voltages. However, at phase B-to-ground voltage, the tester returned 0 V.

What may have caused this grounding and what topics should I look for to circumvent this unintended grounding.

Thank you in advance.
 

iwire

Moderator
Staff member
Location
Massachusetts
Here is an example of corner grounded delta


3_phase_2_wire_grounded_delta.png
 
Hi sir Bob & iwire,


I have strong belief that its not a corner ground as all the remaining panels identical to the one in question registers expected phase-to-ground voltages.


What could have caused that phase grounding of just one panel?


By the way, I really appreciate your lightning fast assistance.


Thanks.
 

Saturn_Europa

Senior Member
Location
Fishing Industry
Occupation
Electrician Limited License NC
Go take measurements on the load side of that transformer and come back and tell us what it is.


This is good advice. And a good place to start troubleshooting.

Snowghost, are you taking readings your self or having an electrician do it? Make sure your wearing arc flash gear when your taking these readings.

I'd power down the transformer before you take the covers. Once the covers are off have everyone stand clear when you power it back up to take your reading s. As the other gentleman said you can probably get the needed info of the name plate
 

kwired

Electron manager
Location
NE Nebraska
Yes, there is a transformer.
then you are not connected to the same place as those other panels, the secondary of that transformer is a new separately derived system and sounds like a good chance it is either corner grounded or ungrounded with B phase faulted to ground.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
then you are not connected to the same place as those other panels, the secondary of that transformer is a new separately derived system and sounds like a good chance it is either corner grounded or ungrounded with B phase faulted to ground.

If this is an SDS and is supposed to be ungrounded, code would require ground detection. So, it would be a good bet that if is there are no ground detection features, it was deliberately grounded. If the system is ungrounded, it is also required to be marked as such by the code, either at the source (the xfmr) or the first means of disconnection. See 250.21.
 

Saturn_Europa

Senior Member
Location
Fishing Industry
Occupation
Electrician Limited License NC
If this is an SDS and is supposed to be ungrounded, code would require ground detection. So, it would be a good bet that if is there are no ground detection features, it was deliberately grounded. If the system is ungrounded, it is also required to be marked as such by the code, either at the source (the xfmr) or the first means of disconnection. See 250.21.


OP has location listed as Manila...........
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
The point about 'phase-to-phase, phase A-to-ground, and phase C-to-ground voltages' leads me to suggest double checking _how_ you are making your voltage measurements.

In particular, are you using a high impedance volt meter which can read 'phantom voltage', meaning voltage across a high impedance path such as insulation leakage?

It would also help us help you if you report all of the voltage measurements; 3 phase to phase, 3 phase to ground, and the expected values.

-Jon
 

kwired

Electron manager
Location
NE Nebraska
If this is an SDS and is supposed to be ungrounded, code would require ground detection. So, it would be a good bet that if is there are no ground detection features, it was deliberately grounded. If the system is ungrounded, it is also required to be marked as such by the code, either at the source (the xfmr) or the first means of disconnection. See 250.21.
I knew all that before posting. The system however will not go on a labor strike and refuse to work just because code was not followed when it was installed, it will follow laws of physics and Ohm's law, Kirchoff's laws, etc will determine what does happen.
 
Hi to All!

I apologize for taking to long to respond.

I've conducted test at loadside of the xfrmr, as you have suggested, and here are the results:

Vab = 240V
Vbc = 240V
Vca = 240V

Vag = 240V
Vbg = 0V
Vcg = 240V

Connection wiring of 500kVA, 480V/240V Dry Type Xfrmr: Delta (P) and Ungrounded Wye (S)

We then traced the connections of the secondary, we found that phase B was body grounded. Is this what may have caused grounding of Phase B? Or are there external factors that contributes to this grounded phase?

We tried disconnecting the panel where we found a grounded phase B, and readings were back to normal (expected readings). Then tried to connect it again, at first all is well but after a couple of minutes, phase B was again grounded.

Also, yes we patterned our code to the NEC with certain ammendments.
 
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