120/208 delta high leg - voltage changed

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rustymetal said:
120/208 High leg delta service
4 Wire- 208v[red A]/120v[black B]/120v[black C]/Green[service] and green[ground rod] bonded on N busbar. 1950's farm building.

I go to this service and problems.. the main breaker - not powering the C phase bus bar.
But a 240v/30A drain waste sub is back feeding into the C phase via the actual pump. The lights being powered via pump leg are quite a show.

The panel gets changed out.

During the change out I may have switched B/C phase.

After I put the meter back in the high leg is reading 320v to ground, 420v to phase B, 240 to C.

How can this be? When I pulled the meter there is clear a unacceptable level of corrosion... service conduit is not connect... fittings are just missing... The meter box is scheduled to be changed. But what did I do wrong?

How could I even change the voltage? Maybe I missed the grounding bushing? Corrosion at fault? Meter put in upside down?
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Did you confirm voltage before your work? Maybe noticed A was high leg but didn't look all that close to exactly what the voltage was and it was wrong from the start? Pump you mentioned may run with that condition, and may go for some time if only runs for short cycles and therefore was never noticed before the main breaker failed which prompted the service call.
 
rustymetal said:
After I put the meter back in the high leg is reading 320v to ground, 420v to phase B, 240 to C.
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So the consensus is that this was caused by a polarity reversal which created a 120º phase shift instead of the 60º needed for a delta.

rustymetal said:
--I checked all the voltages before I began. 208v to ground 240-B, 240-C. 4 Wire. Only 1 taped red and 1 taped green. . Grounding rod comes in different raceway.
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rustymetal said:
No, the B/C line are 120v to ground and 240v on phases. Only the high leg is testing off.
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Perhaps there was an intermittent open connection between the transformer secondary windings that allowed the measurements of 208V, 240V, and 120V. Below is a possible explanation how this could happen even when the windings are reversed from the correct polarity.

As above, let A be the high leg with the two transformer windings tied together at phase C. Assume that the intermittent causes the windings to disconnect from eachother at C, but the C line output is still connected to the winding that provides the high leg A at its other end. This would allow the A-C untapped winding to "float" relative to the center-tapped B-C winding. If there is a load across B-C then that will establish a connection to the other side of the center-tapped winding at B, which is at 180º from C. Therefore both the A-B and A-C voltages would be 240V, and the A-N voltage would be 208V. The B-C voltage would be close to zero, but it was not clear from the above that this was measured.

Another possibility is that the transformer was wired the with correct polarity, and the intermittent open connection causes the same kind of inversion as above but with the disconnection on the other side of the tapped winding. This could explain having 320V A-N, but it wouldn't explain the 420V A-B and 240V A-C because that would require both sides of the tapped winding to be connected.
 
With your floating A-C you would get the 240v as you suggested but the A-N wouldn't be 208v nor would B-C be near 0v. The intemittent inversion doesn't wash either.

The most reasonable explanation is the poco changed something on the transformer bank during the outage.
 
mivey said:
With your floating A-C you would get the 240v as you suggested but the A-N wouldn't be 208v nor would B-C be near 0v. The intemittent inversion doesn't wash either.

The most reasonable explanation is the poco changed something on the transformer bank during the outage.
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OP was there because main breaker failed to close one pole, made changes, then discovered this problem. Did not make it clear whether voltage was correct before his work, possibly was wrong from the start.
 
kwired said:
OP was there because main breaker failed to close one pole, made changes, then discovered this problem. Did not make it clear whether voltage was correct before his work, possibly was wrong from the start.
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He did check before working, see post #16
 
mivey said:
With your floating A-C you would get the 240v as you suggested but the A-N wouldn't be 208v nor would B-C be near 0v. The intemittent inversion doesn't wash either.

The most reasonable explanation is the poco changed something on the transformer bank during the outage.
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The attached might explain better what I was suggesting as a possible cause for the OP's observations.

delta_diags2.jpg
 
Hv&Lv said:
How are you suggesting C became disconnected and then reconnected?
Sorry, I don’t buy it..


I’m thinking maybe voltage wasn’t thoroughly checked before hand
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Well, one connection being intermittently disconnected and reconnected sounds more likely to me than two connections being disconnected, the polarity reversed and then both being reconnected. I was just suggesting an alternative that could explain the OP's posted measurements, but I'm not betting any money it happened that way.
But I agree the voltage might not have been checked thoroughly before changes were made, especially if one were looking for familiar voltages.The 320V and 420V observed are just what you would would expect from a reverse polarity and are also uncommon values. So I don't think there's any question that it must've been reverse polarity.
 
synchro said:
Well, one connection being intermittently disconnected and reconnected sounds more likely to me than two connections being disconnected, the polarity reversed and then both being reconnected. I was just suggesting an alternative that could explain the OP's posted measurements, but I'm not betting any money it happened that way.
But I agree the voltage might not have been checked thoroughly before changes were made, especially if one were looking for familiar voltages.The 320V and 420V observed are just what you would would expect from a reverse polarity and are also uncommon values. So I don't think there's any question that it must've been reverse polarity.
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I also think the with resistive portion of the load you won’t see the full 120 volts
 
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