High Voltage Reading

[Ravenvalor]

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]

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 $]

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]

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]

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....

 

[Smart $]

http://www.powerqualityworld.com/2011/04/ansi-c84-1-voltage-ratings-60-hertz.html

 

[kwired]

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]

http://www.powerqualityworld.com/2011/04/ansi-c84-1-voltage-ratings-60-hertz.html

Interesting, the figures are almost reversed with a higher tolerance of under voltage.

There is a reason behind the UK having +10%. Despite the EU deciding our supply voltage is 230V the suppliers gave them the traditional two finger salute and moved the goal posts, 230+10%=153V.

My supply at this moment 247.8V and so within tolerance.

 

[Smart $]

... 230+10%=153V.
...

Just a little typo there.

230+10%=253V

 

[Tony S]

:lol: OK Smart Aleck

 

[templdl]

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.

 

[kwired]

utility company could even be having voltage regulation issues.

 

[JFletcher]

have you been back or determined the source of the higher voltage?

 

[Ravenvalor]

have you been back or determined the source of the higher voltage?

Thanks for inquiring, I am supposed to go out there tomorrow. They are not too concerned about it since it is a mostly unused warehouse. There is a transformer mounted right above the panel that I will probably open up.

 

[Ravenvalor]

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.

 

[JFletcher]

Thank you for the follow up.