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Discussion Starter #1
Hello all,
Had a question with a problem I am having in our Mill. Currently in all my buckets I am reading a line to line voltage of 595 VAC. The issue I have is with my Line to Ground voltage.
L1 - G -> 409VAC
L2 - G -> 235VAC
L3 - G -> 409VAC

Anyone have an idea on what I should be looking for?
 

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Discussion Starter #3
There are no issues in the MCC, I just noticed this when I was testing to see if there was a fuse blown in the circuit. When I noticed this, I tested the other some other buckets and they all read the same.
 

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Shorted wire...
Without more information, that would be my best guess...
What is your system voltage? Solid grounded neutral or impedance ground?
Any faults showing up? Where are you measuring?
Are you an electrician?
 

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Discussion Starter #5
Yes I am an electrician. I am taking measurements from the top of the fuses on individual buckets. Not showing any faults. Line voltage is 2300 stepped down to 600 in our MCC. The neutral is solid ground from what I can see on the prints.
 

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600 volts on 3 phase is meant to be 347 to ground. 347 x 3 = 1041
409 + 235 + 409 = 1053

That to me looks like the center point of the transformer (if it has one) is not tied to ground.

That may be total wrong but i would start by checking the transformer label rather than the prints.
 

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Are you getting those readings at the bus? Check the xfmr. ground. Could also be a motor on that MCC going bad. If you can, try turning everything off, one at a time until it clears.
 
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looks like a high resistance ground fault on your low leg or a bad neutral connection to me. Do you have any 347V loads? check the ground current at the system bonding or as close to it as you can. that's a wye secondary right? whats neutral to ground voltage? and legs to neutral
 

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It sounds like you have a floating[non grounded] connection now with a high resistance ground on B phase like Wiresmith said. On a floating system, the first phase ground is free, the next one isn't! You need to isolate the fault by shutting down buckets, and then fix the floating neutral on the transformer. If you don't clear the fault and do fix the neutral ground at the transformer, you will suddenly have a full on phase to ground in short order which may destroy whatever is in the conduit or tray with it.
 

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Hello all,
Had a question with a problem I am having in our Mill. Currently in all my buckets I am reading a line to line voltage of 595 VAC. The issue I have is with my Line to Ground voltage.
L1 - G -> 409VAC
L2 - G -> 235VAC
L3 - G -> 409VAC

Anyone have an idea on what I should be looking for?
I would say that it depends on the age of the mill.
Also, and somewhat important/ interesting.
What ampacity is the transformer feeding that MCC or Service?

I would suspect you have a Delta system that either has a decaying intentional grounded B phase or you have an ungrounded Delta with B phase unintentional partially shorted / high impedance ground.

Something like this could have been a problem for 50 years or it could be something new.

I would start by eliminating the unintended ground theory by turning off all of the buckets and then energizing them one by one until you find a problem.
. Mark that bucket, turn it off and see if you find and more.

I suggest this method over turning them off one at a time for obvious reasons.
 

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If it truly is a solidly grounded neutral system, it sounds as though you have a bad N connection and you are reading capacitive voltages to ground. What I’ve seen happen a lot lately is that copper thieves are thinking that exposed GECs are “safe” connections to cut and steal, but you don’t know it has happened until you find squirrelly readings like this.

Either that or you have a single phase load connected somewhere with an open or high resistance on the N connection. In 600/347 V systems, the 347 is sometimes used for lighting. Start looking there first if that’s the case.
 
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