3 phase voltage fluctuations with current spikes

M

Master_Krafter

Member
Location
Seattle, WA
Occupation
Electrical contractor
Service call for frequent shutdown of computers and lighting flickers.

3 phase service to an office warehouse. Mostly 129v circuits aside from basic hot water(30a 208v) and ac(17a 208v). Showing some wild readings.
LN 1 - G 134v
LN 2 - G 115v
LN 3 - G 111v
this is with basic operation.
Add a microwave on LN 3 and the voltage jumps
LN 1 - G 140v
LN 2 - G 118v
LN 3 - G 101 - 108v
utility provider is reporting 90a spikes but no significant voltage changes. Grounding and bonding is solid. Anyone have some knowledge to share?
 

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Sounds like a neutral issue to me.
If you add all the voltages reading and divide by 1.73 ( square root of 3)or 208. Then I would say it's a neutral issue.

Pretty sure you meant 120 v circuits.
 
Where’s your meter, it’s possible you have a bad connection in your meter or gear compartment? That service can’t come in straight from the utility transformer to that panel.
 
Also changed phases on a single phase sub panel from LN-2/LN-3 to LN-1/LN-2. That did seem to help the rise and drop in voltage slightly. Have not seen it over 136v LN-1 and not under 106v LN-3
Slight improvement but not solved
 
Voltage instability where the L-L is good but L-N voltage changes with L-N loads is a pretty solid indicator of an issue with the neutral.

The L-N voltages will be stable up to the point where the neutral is weak or open. If there are multiple neutral to ground bonds, then parallel current flow on the grounded metal can mask a problem with the neutral.

If you can get a large load that fluctuates in a well defined fashion (say a 500W incandescent lamp on a blinker) this can help trace issues.
 
ptonsparky said:
Underground?
Click to expand...
Get the utility to run the beast of burden test at the meter. If the problem exists there, then it’s a problem on the power from the utility. It sure sounds like Winnie said, if you’ve got a neutral problem it can be masked or covered up by multiple bond locations.
 
ptonsparky said:
I cast another vote for a Neutral issue.
Click to expand...
Just had one recently that turned out to be a bad meter connection. Utility measured at their pole and proclaimed it was all good at their end, but we were seeing voltage fluctuations. Convinced the utility to pull the meter, there it was, hiding under there. Had to replace the meter socket.

User kept insisting this was a utility problem and wanted them to absorb the replacement costs for the socket and the damaged equipment (a couple of small VFDs and a fried PLC power supply)… I had to set him straight about who owns what. He was not a happy camper.
 
winnie said:
Voltage instability where the L-L is good but L-N voltage changes with L-N loads is a pretty solid indicator of an issue with the neutral.

The L-N voltages will be stable up to the point where the neutral is weak or open. If there are multiple neutral to ground bonds, then parallel current flow on the grounded metal can mask a problem with the neutral.

If you can get a large load that fluctuates in a well defined fashion (say a 500W incandescent lamp on a blinker) this can help trace issues.
Click to expand...
Are you say potentially an internal neutral issu? Open or loose
 
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