I'm a plant engineer in an industrial facility that is supplied with a 240V Corner Grounded Delta System. I was called out to a machine that had tripped an O/L on motor. I reset the trip then disconnected power to the machine to measure voltage on the supply side of the disconnect. When I measured the voltage, the voltage was cycling from 240V to 160V up and down consistently. I've never seen this before...at a loss...it went away for sometime but when I went back later to measure it was back...any suggestions?
Voltage Cycling?
- Thread starter rjaruse
- Start date
- Status
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
A single voltage reading is almost meaningless for troubleshooting.
What are these 6 voltages?
L1-L2
L2-L3
L3-L1
L1-G
L2-G
L3-G
Where did you measure the voltage, at the motor, the panel, or both?
I would not be surprised with fluctuating voltages on an ungrounded system, but you said yours is corner grounded. It almost sounds like an arcing fault.
What are these 6 voltages?
L1-L2
L2-L3
L3-L1
L1-G
L2-G
L3-G
Where did you measure the voltage, at the motor, the panel, or both?
I would not be surprised with fluctuating voltages on an ungrounded system, but you said yours is corner grounded. It almost sounds like an arcing fault.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Were your cycling measurements taken at the equipment? Were any loads in the facility affected by this cycling? How long did it last?
I assume you have three conductors run to your equipment. Did you measure from your grounded conductor (actually L3) and your grounding conductor? Because these are supposed to be bonded only at the service entrance, we would expect there to be some voltage between them at a piece of equipment.
JohnJ0906
Senior Member
- Location
- Baltimore, MD
Equipment Grounding Conductor
As opposed to GEC - Grounding Electrode Conductor
Saturday/Today I disconnected power that fed the panel that fed this machine and measured voltage on line side of disconnect which is within 5 ft. of main disconnect/meter for facility.
L1 - grnd = cycles at low voltage 0V - 50V
L2 - grnd = cycles at 240V to 160V
L3 - grnd = cycles at 240V to 190V
L1 - L2 = 240V steady
L1 - L3 = 240V steady
L2 - L3 = 240V steady
puzzled????
I'm assuming it's corner grounded delta because L1 has always been 0V to ground.......is it possible that I have ungrounded delta and L1 is grounding out?
L1 - grnd = cycles at low voltage 0V - 50V
L2 - grnd = cycles at 240V to 160V
L3 - grnd = cycles at 240V to 190V
L1 - L2 = 240V steady
L1 - L3 = 240V steady
L2 - L3 = 240V steady
puzzled????
I'm assuming it's corner grounded delta because L1 has always been 0V to ground.......is it possible that I have ungrounded delta and L1 is grounding out?
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