253V or higher voltage at some receptacles on a 120/240V, single phase service voltage system

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curious101

Senior Member
Location
Atlanta, GA, USA
Hi there,

I would like to find out if anybody has encountered anything similar to the below described:
120/240V, single phase service for a gas station/convenience store. They are experiencing 253V or in some cases higher than 260V at some receptacles.
Could this be caused by power company service voltage fluctuations? Any other suggestions?

Thanks!
 
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Hv&Lv

Senior Member
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Engineer/Technician
Yes. Regulator is off a couple of steps.
either that or the transformer is going bad.

Call the POCO now
 
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Hv&Lv

Senior Member
Location
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Occupation
Engineer/Technician
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curious101

Senior Member
Location
Atlanta, GA, USA
curious101 said:
Hi there,

I would like to find out if anybody has encountered anything similar to the below described:
120/240V, single phase service for a gas station/convenience store. They are experiencing 253V or in some cases higher than 260V at some receptacles.
Could this be caused by power company service voltage fluctuations? Any other suggestions?

Thanks!
Click to expand...
These are L6-30 receptacles and they are fed through buck boost step down transformer because we have to step down the voltage from 240V to 208V (per the equipment manufacturer's requirements). But this should not cause the voltage at the receptacles to go up, correct? So it must be coming from the power company voltage fluctuations, correct? Thanks!
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
curious101 said:
These are L6-30 receptacles and they are fed through buck boost step down transformer because we have to step down the voltage from 240V to 208V (per the equipment manufacturer's requirements). But this should not cause the voltage at the receptacles to go up, correct? So it must be coming from the power company voltage fluctuations, correct? Thanks!
Click to expand...
Wait, wait, wait...
You said nothing about another XF involved

What is the voltage supplying the building now. At the main panel, not behind any other transformers
Now it’s not making sense..

you have 129 where you should have 208??
 
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Hv&Lv

Senior Member
Location
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Occupation
Engineer/Technician
curious101 said:
The main service voltage is 120/240V, single phase.
Click to expand...
That’s not what I asked. What is the voltage supplying the building.
You muddied the water with the buck boost coming in the conversation late.
 
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curious101

Senior Member
Location
Atlanta, GA, USA
Hv&Lv said:
Wait, wait, wait...
You said nothing about another XF involved

What is the voltage supplying the building now. At the main panel, not behind any other transformers
Now it’s not making sense..

you have 129 where you should have 208??
Click to expand...
The 129 didn't come from me. That comment came from somebody else as their own experience. 129V does not apply to my original thread.
 
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Hv&Lv

Senior Member
Location
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Occupation
Engineer/Technician
curious101 said:
The 129 didn't come from me. That comment came from somebody else as their own experience. 129V does not apply to my original thread.
Click to expand...
253-260 equates to 126.5-130v
If you have 260v ahead of the step down XF at the meter call the POCO.
If you have that voltage after the step down XF call an electrician
 
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curious101

Senior Member
Location
Atlanta, GA, USA
Hv&Lv said:
That’s not what I asked. What is the voltage supplying the building.
You muddied the water with the buck boost coming in the conversation late.
Click to expand...
I did not mean to muddy up anything, sorry.... I just wanted to further clarify the situation. I can't change my statement which has been true from the beginning: the building service is 120/240V single phase. There is 120/240V, single phase on the secondary of the power utility transformer which comes in as a service to our building.
 
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d0nut

Senior Member
Location
Omaha, NE
It sounds like your buck/boost transformer is connected incorrectly. Are you sure you aren't connected to boost the voltage rather than configured to buck it? If the transformer is connected correctly, the utility company would be providing about 300V instead of the 240V to get 260V at a receptacle that should be a 208V receptacle.
 
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curious101

Senior Member
Location
Atlanta, GA, USA
d0nut said:
It sounds like your buck/boost transformer is connected incorrectly. Are you sure you aren't connected to boost the voltage rather than configured to buck it? If the transformer is connected correctly, the utility company would be providing about 300V instead of the 240V to get 260V at a receptacle that should be a 208V receptacle.
Click to expand...
That was my suspicion too, but they claim that they have the correct transformer. The problem is that I am not at the site. Thank you!
 
synchro

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
d0nut said:
It sounds like your buck/boost transformer is connected incorrectly. Are you sure you aren't connected to boost the voltage rather than configured to buck it?
Click to expand...
Yes. If the buck boost has 16/32V output windings, it might be connected now in a boost configuration like Fig. G below (which would add 16V to a 240V input) instead of the buck configuration in Fig. I necessary to get a ~ 208V output.

Buck-boost_connections.png

Figures are from pg. 9 of Acme Electric doc at:

 
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