step down transformer

thorn949

Member
Have not researched yet but secondary side of transformer is putting out 190 volts and not 208 volts. Panel is 125 amp 120/208 volt, 45 KVA transformer with a 65 amp breaker for secondary overcurrent protection 3 phase. is this normal plus or minus 10% ? Check center tap to increase voltage?
 

Besoeker

Senior Member
Have not researched yet but secondary side of transformer is putting out 190 volts and not 208 volts. Panel is 125 amp 120/208 volt, 45 KVA transformer with a 65 amp breaker for secondary overcurrent protection 3 phase. is this normal plus or minus 10% ? Check center tap to increase voltage?
If it's three phase wye (star) as your description indicates, it would have a star point, not a centre tap. The star point is simply the common point where the three secondary windings are connected together. You can't use it to alter the voltage.
 

iwire

Moderator
Staff member
Have not researched yet but secondary side of transformer is putting out 190 volts and not 208 volts. Panel is 125 amp 120/208 volt, 45 KVA transformer with a 65 amp breaker for secondary overcurrent protection 3 phase. is this normal plus or minus 10% ? Check center tap to increase voltage?
The first step is to determine if the supply voltage is correct.
 

templdl

Senior Member
Have not researched yet but secondary side of transformer is putting out 190 volts and not 208 volts. Panel is 125 amp 120/208 volt, 45 KVA transformer with a 65 amp breaker for secondary overcurrent protection 3 phase. is this normal plus or minus 10% ? Check center tap to increase voltage?
Please provide the complete name plate information from your transformer as well as what the actual meaured primary voltage that is feeding the transformer is and we can proceed from there.
 

kwired

Electron manager
Primary side likely has multiple "taps" to connect incoming supply to, or indirectly connects the incoming supply terminal to the correct "tap" of the winding.

Check incoming voltage and adjust taps accordingly and it will change what you see for secondary voltage.
 

iwire

Moderator
Staff member
Primary side likely has multiple "taps" to connect incoming supply to, or indirectly connects the incoming supply terminal to the correct "tap" of the winding.

Check incoming voltage and adjust taps accordingly and it will change what you see for secondary voltage.
If the supply voltage is low the first thing I would do is try to find out why and try to figure out if it is going to stay that way.

Adjusting the taps is a bad move if the supply voltage varies a lot due to overvoltage issues.
 

kwired

Electron manager
If the supply voltage is low the first thing I would do is try to find out why and try to figure out if it is going to stay that way.

Adjusting the taps is a bad move if the supply voltage varies a lot due to overvoltage issues.
True if voltage varies you may have other issues, I didn't do the greatest job of trying to say it is possible the taps were never set to right position in the first place.

Changing taps is not a good way to compensate for voltage drop, when load decreases you may very well end up with too high of voltage at transformer secondary, you need to set taps for the most steady state expected input voltage.
 
As mentioned before, first check the supply voltage and make sure that it is correct. Most utilities have acceptable tolerances of plus or minus 5%. This would put your minimum voltage at 197.6 for a 208 service. If you are falling below this at the transformer, go to the main panel and check the feeders. If they are below this, then contact the utility. This is something that should be done sooner rather than later because low voltage can be just as bad for equipment as high voltage in some instance.
 

kwired

Electron manager
As mentioned before, first check the supply voltage and make sure that it is correct. Most utilities have acceptable tolerances of plus or minus 5%. This would put your minimum voltage at 197.6 for a 208 service. If you are falling below this at the transformer, go to the main panel and check the feeders. If they are below this, then contact the utility. This is something that should be done sooner rather than later because low voltage can be just as bad for equipment as high voltage in some instance.
Chances are OP is stepping down from 480 volts. Also utility possibly delivers 480 volt service voltage within tolerable ranges, but they can't do anything about voltage drop in the customer wiring should that be where the reduction is happening.
 
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