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Old 09-13-2018, 05:42 PM   #1
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Default Troubleshoot question (Odd problem...)

I was called down to troubleshoot a warehouse that was having a voltage problem at their switch gear. I talked to the warehouse maintenance man and he said that it's typically 277/480 but now when he reads from A phase to ground, he reads 480. B phase to ground, he reads 480. C phase to ground, he reads 0... Which would lead me to believe it was a corner tapped Delta system. But it couldn't be, I looked up at the transformer and it is Wye wired... He even said that it used to be 277/480 until recently. What is even more strange is that when I look at the transformer up on the power line, everything looks correct minus the fact that there is no neutral going into the building.....????? I'll add pictures to this post, but to explain, you have the 3 hots on the power line and then the neutral will travel bellow the 3 hots. Those 3 hots are wired to the transformer and go into the building, the neutral wire DOES NOT hit the transformer, it just goes directly into the building....???

Okay I've probably confused everyone at this point, but let me continue... Long story short I ended up finding the issue. Whenever I turn off this 2 pole breaker, all the voltages correct itself. Everything goes back to normal, A phase 277, B phase 277, C phase 277, and phase to phase is 480... This 2 pole breaker feeds a bunch of LED lights that were recently installed. Each LED light has a transformer inside of it that transforms 480 down to 277, then the 277 feeds the driver which powers the lights.

How could these LED fixtures be causing this issue? I'm so confused, how can they be making the entire switch gear 480 A phase to ground, 480 B phase to ground, 0 C phase to ground when the lights are on? Then when I turn off the 2 pole breaker, the entire problem solves itself. May I add none of these 277/480 panels have a neutral. But when you go from ground to phase, you get 277..........

Also, how can the switch gear be 277/480 when there is no neutral coming off the transformer outside on the power line? The neutral just goes directly into the building without hitting the transformer first. It just makes no sense at all. Here are pictures.
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Last edited by JasonCo; 09-13-2018 at 05:47 PM.
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Old 09-13-2018, 06:05 PM   #2
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Where to start?

I'm trying to wrap my head around the statement "all the voltages went back to normal"

And I'm trying to understand your trouble shooting skills that led you to turn off a 2 pole breaker.


There must be more to this.
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Old 09-13-2018, 06:15 PM   #3
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The company allowed me to do whatever I needed to do to find the problem. Meaning I was able to turn off panels/breakers/etc... Anything to fix this. So long story short I decided that the problem could be an issue on the load side of something, that something is causing this voltage problem on the load side of the breakers. I've already ran into situations like this so I said **** it... I started turning off main panel breakers and when I turned off the main breaker that went to one of the 277/480 panels, the problem went away. So I then turned the panel back on, and started turning off individual breakers, and sure enough I turned one of the 2-pole breakers off and the voltage problem went away. When I turned off this 2-pole breaker, it would kill the LED lights in the warehouse. They said that someone recently installed those LED lights and that was about the same time they started having this voltage problem. So yeah, that's how I figured it out.

I didn't have a scissor lift today so tomorrow I will go back with a scissor lift and figure out which fixture is causing this problem, or where on the load side of the 2-pole is causing the problem. It just seams crazy to me that these LED fixtures, even though they are all working just fine, are causing this crazy voltage problem for the entire service.

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Old 09-13-2018, 06:18 PM   #4
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Thats really odd and i would call the poco.

The transformers look like they have a wye connection (one wire the goes between the transformers but i do not see where it is tied to ground)

Im not 100% sure what would happen if you removed the ground connection on a wye set up and grounded a phase directly to the building. (short on c phase going to the lights).

Its not unusual to have a 480v 3 phase with no neutral which would make sense that the lights have a power transformer thats 480 to 277. The company i work for has no neutral on there system but the wye center point is tied to ground to keep the phases at 277v.

I would check with a second meter then call the poco to check that the wye is grounded. I would also meg the light circuit to see if c phase ohms to ground. ( i may be totally wrong but at least the poco would be able to assist by explaining why the wye seems to be floating).
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Old 09-13-2018, 06:23 PM   #5
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Originally Posted by gpop View Post
Thats really odd and i would call the poco.

The transformers look like they have a wye connection (one wire the goes between the transformers but i do not see where it is tied to ground)

Im not 100% sure what would happen if you removed the ground connection on a wye set up and grounded a phase directly to the building. (short on c phase going to the lights).

Its not unusual to have a 480v 3 phase with no neutral which would make sense that the lights have a power transformer thats 480 to 277. The company i work for has no neutral on there system but the wye center point is tied to ground to keep the phases at 277v.

I would check with a second meter then call the poco to check that the wye is grounded. I would also meg the light circuit to see if c phase ohms to ground. ( i may be totally wrong but at least the poco would be able to assist by explaining why the wye seems to be floating).
Good idea, yeah I never did a continuity test to see if C is bonded to ground. I just figured the breaker would trip if C was bonded to ground? (Assuming the building is properly grounded to Earth?) Also, I never realized this was common, for transformers to tap the Y center point to ground to get the 277v to ground. Interesting stuff... Thanks man!

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Old 09-13-2018, 06:52 PM   #6
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Default Troubleshoot question (Odd problem...)

I have seen reading like that before and it ended up being a ground fault that was causing it. The system was 277/480 Y but they did not use the natural and just bonded it. The building also had a (HRG) high resistance ground fault detectors.


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Old 09-13-2018, 07:06 PM   #7
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Quote:
Originally Posted by gpop View Post
Im not 100% sure what would happen if you removed the ground connection on a wye set up and grounded a phase directly to the building. (short on c phase going to the lights).
Quote:
Originally Posted by Ctsparky93 View Post
I have seen reading like that before and it ended up being a ground fault that was causing it. The system was 277/480 Y but they did not use the natural and just bonded it. The building also had a (HRG) high resistance ground fault detectors.
One thing though I'm pretty curious about. If C phase (The phase that was reading 0 to ground) has a ground fault, why would that not trip the breaker? Not sure if this is what is happening, but just saying, if this is the reason, why would it not be tripping the breaker? You mentioned that C phase could be grounded directly to building.

I assume the building is properly grounded to Earth? Idk... Maybe it's not? Maybe the fact that the panels don't have a neutral could be contributing to this somehow? Idk, just thinking out loud
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Old 09-13-2018, 07:35 PM   #8
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Probably an ungrounded service? Something wrong with the new lights that cause one phase to short to ground. What was the phase to phase voltage when the problem was there? I bet phase to phase was still 480 on all three phases.
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Old 09-13-2018, 08:19 PM   #9
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I have see that before with floating wye system and with the LED driver it may have just enough current leaking to the ground but not enough to trip the breaker so that is one of the curpit.

If POCO replace the overhead poles and did not hook up the neutral connection it can cause to run to sorta like corner grounded system if your tester show it so get a properly rated wiggly to verify the actual voltage from line to ground and line to line.

the other possibitly you mention 480X277 volt transformer that can be a other issue with grounding one one of the conductor. so you may got a stinky one can cause a lot of headache with bad transformer.
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Old 09-13-2018, 08:33 PM   #10
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One thing though I'm pretty curious about. If C phase (The phase that was reading 0 to ground) has a ground fault, why would that not trip the breaker? Not sure if this is what is happening, but just saying, if this is the reason, why would it not be tripping the breaker? You mentioned that C phase could be grounded directly to building.

I assume the building is properly grounded to Earth? Idk... Maybe it's not? Maybe the fact that the panels don't have a neutral could be contributing to this somehow? Idk, just thinking out loud
You can ground any side of a secondary transformer on one phase and nothing will happen. Ground both sides and its a short circuit and it will trip breakers and burn wires. If the whe connection is not grounded correctly then only one side is being grounded when you turn on the lights.

Thankfully they are not using 277v or there would be smoke everywhere.

Sry but if i see voltages that point to a major problem i call for help (poco). They are not set up to run a floating neutral or there would be warnings and special monitors to shut the power off if there was a fault.
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Old 09-13-2018, 08:41 PM   #11
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You can ground any side of a secondary transformer on one phase and nothing will happen. Ground both sides and its a short circuit and it will trip breakers and burn wires. If the whe connection is not grounded correctly then only one side is being grounded when you turn on the lights.

Thankfully they are not using 277v or there would be smoke everywhere.

Sry but if i see voltages that point to a major problem i call for help (poco). They are not set up to run a floating neutral or there would be warnings and special monitors to shut the power off if there was a fault.
Earlier though you were saying that there might be a short on C phase (or do you mean ground fault from C phase to ground somewhere in the lights?), which is causing a reading of 0 from C to ground. But if this was the case, wouldn't it cause the breaker to trip?

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If the whe connection is not grounded correctly then only one side is being grounded when you turn on the lights.
What do you mean by this?
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Old 09-13-2018, 09:01 PM   #12
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Google corner ground delta and see how it is grounded. If the neutral connection isn’t grounded on your star, you can ground any phase without a issue like a delta, until you get a accidental ground on another.
That’s what the consensus here is thinking (I think!) If the light circuit has a ground on a phase wire, then there is your system ground all of a sudden.
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Old 09-13-2018, 09:07 PM   #13
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On 480 wye you ground the wye which means that every phase to ground will equal 277v. If you do not ground the wye then it will float based on the load.

On a 480v plant it doesnt really matter as everything is going phase to phase so any reading to ground is basically usless.

Now the kicker is on a ungrounded wye system if one phase is shorted to ground (a wire gets nicked and the phase touches ground) you will read up to 480v on the other phases to ground. It also means that if you touch a wire you will not be shocked by 277v, you will be shocked by 480v instead.
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Old 09-13-2018, 09:26 PM   #14
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Google corner ground delta and see how it is grounded. If the neutral connection isn’t grounded on your star, you can ground any phase without a issue like a delta, until you get a accidental ground on another.
That’s what the consensus here is thinking (I think!) If the light circuit has a ground on a phase wire, then there is your system ground all of a sudden.
But the problem though is that the transformer is wired up as a Wye system, but without a neutral. I mean the neutral is coming in from the power line, but instead of wiring it up to the transformer up on the power line, it just goes straight into the weather head, which is odd to me... The picture shows this.

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Old 09-13-2018, 09:37 PM   #15
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On 480 wye you ground the wye which means that every phase to ground will equal 277v. If you do not ground the wye then it will float based on the load.

On a 480v plant it doesnt really matter as everything is going phase to phase so any reading to ground is basically usless.

Now the kicker is on a ungrounded wye system if one phase is shorted to ground (a wire gets nicked and the phase touches ground) you will read up to 480v on the other phases to ground. It also means that if you touch a wire you will not be shocked by 277v, you will be shocked by 480v instead.
In this case the Wye system has no neutral, just 3 phases coming off the transformer, and that's it. But in normal operation without the LED's being on, you read 277 to ground on each phase, which tells me that the center of Wye is grounded. So in this scenario, where I DO have a ground coming off the center of my Wye. I can ground C Phase and it'll start reading A to Ground 480v, B to Ground 480v, C to ground 0? EVEN THOUGH the center of Wye is grounded?
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Old 09-14-2018, 05:04 AM   #16
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On a floating delta you will read ~277 volts phase to ground due to capacitance, so I see no reason a star that is floating intentionally or by accident would act differently. It sounds as though the light circuit is providing the system ground when on, that needs addressed then the power co. needs involved. It could have been a delta system at one time that was changed to a star, and a neutral wasn't landed/grounded properly, things happen.
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Old 09-14-2018, 05:39 AM   #17
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I think if you have a floating wye and a ground fault on C you'll see

V(A)(C) = V(A)(G) = 480
V(B)(C) = V(B)(G) = 480
V(A)(B) = 480
V(C)(G) = 0
V(A)(N) = 277
V(B)(N) = 277
V(C)(N) = V(N)(G) = 277

So if that's what you're seeing with the circuit energized, there's very likely a ground fault on the C leg of that circuit.

With an ungrounded system the first ground fault is free, the next one is boom / zap. I guess even if it's an unintentionally ungrounded system that's the case. You're just missing the ground fault indicators, the maintenance man did what they'd do, raise an alarm.
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Old 09-14-2018, 04:43 PM   #18
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Lectricity is hard.

I never understood any of the transformer stuff other than the vey basics.

Good luck. Ill check back and maybe learn something.
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