High Voltage Reading

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Ravenvalor

Senior Member
Hello,

As soon as I saw this problem I knew this would be a good question for this forum.

Can anyone please explain why the voltage readings on a 200-amp, 3-phase possible 208/120-volt panel is reading 132, 127 and 132 volts on phases A, B and C respectively? The panel is located in a very old warehouse for a very old textile mill along the textile belt of the southeast. I heard that the power along the textile belt was a little funny but I do not think this is what I am seeing now.

Thank you,
 

JFletcher

Senior Member
Location
Williamsburg, VA
Hello,

As soon as I saw this problem I knew this would be a good question for this forum.

Can anyone please explain why the voltage readings on a 200-amp, 3-phase possible 208/120-volt panel is reading 132, 127 and 132 volts on phases A, B and C respectively? The panel is located in a very old warehouse for a very old textile mill along the textile belt of the southeast. I heard that the power along the textile belt was a little funny but I do not think this is what I am seeing now.

Thank you,

Wired off a +5% tap or buck/boost 10% tap would be my guess. Maybe the xfmr has a +10% tap. What do you mean by "three phase possible"? What are the voltages L-L?
 

Smart $

Esteemed Member
Location
Ohio
How heavily loaded was this panel (and panels between it and the service, if any) when you measured?

If minimally loaded, perhaps someone used voltage taps on a transformer to make up for voltage sag when heavily loaded, or during motor starts.
 

Tony S

Senior Member
Are there any statutory values for supply voltage regulation?

The UK power companies have statutory limits of +10/-6% your supply would just squeeze in at +9.9% so they would do nothing (as per usual).

Remote areas on long OH lines are notorious for voltage variations. Trying to get anything done about them is virtually impossible.
 

Ravenvalor

Senior Member
Thanks for all of the great advice.

First, I have to admit I did not even check line to line. :ashamed1:..... I was in too big of a rush to get out of there on a Saturday afternoon. There is an old label on the panel cover stating "208/120 volt" that has been painted over and next to it is another old label on the panel cover stating "220/120 volt".

Also, this is not a power company problem because the voltage is correct elsewhere in this facility.
As far as legal limits, I am not sure what they are but I will ask the inspector on Monday.
Are there any 'best practices' limits that you all recommend?

Have a great Sunday....
 

kwired

Electron manager
Location
NE Nebraska
Is the source for this separately derived within the facility? If so check out the primary side taps as has been already mentioned.
 

Tony S

Senior Member

templdl

Senior Member
Location
Wisconsin
Hello,

As soon as I saw this problem I knew this would be a good question for this forum.

Can anyone please explain why the voltage readings on a 200-amp, 3-phase possible 208/120-volt panel is reading 132, 127 and 132 volts on phases A, B and C respectively? The panel is located in a very old warehouse for a very old textile mill along the textile belt of the southeast. I heard that the power along the textile belt was a little funny but I do not think this is what I am seeing now.

Thank you,
Am I to assume that the L-L voltages aste high also? You also omitted as to where the primary taps are set at and what the primary L-L voltages are. With oiut that information it would only lead to speculation so much that one could even suggest that there is a leading power fasctore which would be unlikely though. With incomplete information it results in only guesses.
 

Ravenvalor

Senior Member
Recap

Recap

I looked at the transformer that feeds the panel on Thursday and found that it was tapped (7-8) for maximum voltage. So the elegant solution would be to move the jumper to probably 3-4.

I also noticed the burnt jumper 7-8 and lug on phase H2. This explains why 2 - of the phases were 135volts and one was 127volts. This phase was only 127volts.


Thanks for the great help.
 

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