Voltage difference

A

anbm

Senior Member
Two same size motors are located in same room, power from same electrical panel but each motor receives a difference voltage,
what could be the issue?
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Is this voltage difference under load or with the motors off?
and what are the voltages you are seeing
 
A

anbm

Senior Member
Hv&Lv said:
Is this voltage difference under load or with the motors off?
and what are the voltages you are seeing
Click to expand...
When both motors run, 480/3 is system voltage, the client mentions the voltage difference around 15-17V.
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Voltage imbalance is a big deal to a motor.


Measure and record the voltage on each power lead. (L 1, L 2, L 3 )
Change all three power leads as follows: L 1 to L 2, L 2 to L 3, L 3 to L 1.
Measure and record voltage on each lead again. (L 1, L 2, L 3 )
If the imbalanced leg follows the motor lead, then a problem exists somewhere within the pump cable, connections, or stator winding.
If the imbalanced leg stays on the same control box terminal and jumps to a different motor lead number, then the problem is with the supply or control box.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
anbm said:
When both motors run, 480/3 is system voltage, the client mentions the voltage difference around 15-17V.
Click to expand...
The way that is worded, it could mean that the two motor are different FROM EACH OTHER by 15-17V, or that the voltage AT BOTH MOTORS is 15-17V lower than the 480V line. Those are two totally different issues.

If it is the first thing, different from each other, 3.5% delta could easily be explained by the things that HV&LV mentioned.

If it's the second issue and they are just complaining that the motor terminal voltage is 15-17V lower than 480V when the motors are running, that's just someone not knowing how things work...
 
A

anbm

Senior Member
Jraef said:
The way that is worded, it could mean that the two motor are different FROM EACH OTHER by 15-17V, or that the voltage AT BOTH MOTORS is 15-17V lower than the 480V line. Those are two totally different issues.

If it is the first thing, different from each other, 3.5% delta could easily be explained by the things that HV&LV mentioned.

If it's the second issue and they are just complaining that the motor terminal voltage is 15-17V lower than 480V when the motors are running, that's just someone not knowing how things work...
Click to expand...
15V-17V voltage drop, i.e. 460V-463V was recorded at one motor but not the other motor. Sorry for the confusion...
 
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