# Weird voltage at main



## Randy82 (Jan 25, 2021)

Last night we had a power surge at the factory I work maintainence at. Our furnace ovens went down due to it. Upon reigniting we were unable to get the combustion fan to start. Checked fuses, which were ok, but upon checking voltages from phase to phase we were getting 480. That part is good. When I checked phase to ground, phase c- 345, b-345, a-136. That is where it got weird. All of the other 3 phase motors fired so we knew it wasn’t a voltage issue; turned out being a contact issue, but I still don’t understand the voltage on phase A. Anyone have any ideas?


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## Southeast Power (Jan 18, 2009)

Randy82 said:


> Last night we had a power surge at the factory I work maintainence at. Our furnace ovens went down due to it. Upon reigniting we were unable to get the combustion fan to start. Checked fuses, which were ok, but upon checking voltages from phase to phase we were getting 480. That part is good. When I checked phase to ground, phase c- 345, b-345, a-136. That is where it got weird. All of the other 3 phase motors fired so we knew it wasn’t a voltage issue; turned out being a contact issue, but I still don’t understand the voltage on phase A. Anyone have any ideas?


I’m concerned with all of those phase to ground voltages.


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## gpop (May 14, 2018)

345+345+136= 826 / 3 = 275 to 276v

If its 480v delta then you have a heavy load on 2 phases. If its a 277/480v Y then you have a bad neutral connection. If you are using any phase to neutral (277v) you probably have a little smoke.
So what kind of transformer do you have ?.

Bad contractor contactor would make a huge single phase condition (2 phases) on a delta transformer.


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## Randy82 (Jan 25, 2021)

gpop said:


> 345+345+136= 826 / 3 = 275 to 276v
> 
> If its 480v delta then you have a heavy load on 2 phases. If its a 277/480v Y then you have a bad neutral connection. If you are using any phase to neutral (277v) you probably have a little smoke.
> So what kind of transformer do you have ?.
> ...


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## Randy82 (Jan 25, 2021)

I wish I could answer that for you or even be able to look at the transformer, but our safety department doesn’t allow us to go into the subs. There is 12470 there and as they say, we are not qualified to be around that.


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## kb1jb1 (Nov 11, 2017)

gpop said:


> 345+345+136= 826 / 3 = 275 to 276v
> 
> If its 480v delta then you have a heavy load on 2 phases. If its a 277/480v Y then you have a bad neutral connection. If you are using any phase to neutral (277v) you probably have a little smoke.
> So what kind of transformer do you have ?.
> ...


Were you being facetious when you said " Bad contractor would make a huge single phase......."or was it a typo?
Sometimes when I re-read some of the things I type, I could almost swear someone is moving the keys on my keyboard.


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## 460 Delta (May 9, 2018)

gpop said:


> 345+345+136= 826 / 3 = 275 to 276v
> 
> If its 480v delta then you have a heavy load on 2 phases. If its a 277/480v Y then you have a bad neutral connection. If you are using any phase to neutral (277v) you probably have a little smoke.
> So what kind of transformer do you have ?.
> ...


It's possible he has a floating Delta with a ground fault that hasn't fully bolted down yet, or the ground bond on a corner ground is bad. That could account for the odd phase to ground/neutral voltages. Floating Deltas were the hot ticket in foundries like I'm thinking the OP is talking about, but I may be reading too much into it also. Floating Deltas were also the stuff in R-Mix plants too for some reason  .


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## oldsparky52 (Feb 25, 2020)

What were the voltages when things were normal? What configured service do you have? Wye, Delta (grounded or not) ?


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## gpop (May 14, 2018)

kb1jb1 said:


> Were you being facetious when you said " Bad contractor would make a huge single phase......."or was it a typo?
> Sometimes when I re-read some of the things I type, I could almost swear someone is moving the keys on my keyboard.



Sorry that was a typo.


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## splatz (May 23, 2015)

Did you measure voltage with a low Z meter?


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## gpop (May 14, 2018)

Randy82 said:


> I wish I could answer that for you or even be able to look at the transformer, but our safety department doesn’t allow us to go into the subs. There is 12470 there and as they say, we are not qualified to be around that.



In that case im sure your company has a service contract with poco or a contractor. Time to reach out for some assistance.


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## just the cowboy (Sep 4, 2013)

460 Delta said:


> It's possible he has a floating Delta with a ground fault that hasn't fully bolted down yet, or the ground bond on a corner ground is bad. That could account for the odd phase to ground/neutral voltages. Floating Deltas were the hot ticket in foundries like I'm thinking the OP is talking about, but I may be reading too much into it also. Floating Deltas were also the stuff in R-Mix plants too for some reason  .


Nice catch. Yes it is because they can take a fault and keep running with one fault till they can empty a pour.
Cowboy


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## ScooterMcGavin (Jan 24, 2011)

If it’s a proper ungrounded system you should have ground indicator lights/ ground fault alarm to tell you there is a ground condition. In theory they are better but they can be quite dangerous. They are setup on the assumption that the ground will be addressed quickly and you don’t have to blow up your equipment when it fails. 

Often times it isn’t and then you end up with what I call “double fault syndrome”. You have a ground on phase say A phase. Now your potential to ground is 480V so something else fails on B or C phase and two pieces of equipment blow up at once. It’s also bad for the breakers because they’re having to interrupt a phase to phase fault through a single pole of the breaker. 

Intermittent grounds are a problem too because they can cause transient overvoltages much higher than the system voltage which stresses the insulation on your whole system. 

It doesn’t necessarily have to be an ungrounded delta. It could be an ungrounded wye as well. I’ve worked on a handful of systems setup that way.


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## cuba_pete (Dec 8, 2011)

just the cowboy said:


> Nice catch. Yes it is because they can take a fault and keep running with one fault till they can empty a pour.
> Cowboy


Hopefully there's a little light bulb that blinks, or some such.


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## just the cowboy (Sep 4, 2013)

cuba_pete said:


> Hopefully there's a little light bulb that blinks, or some such.


In systems like this, the problem is the bulbs burn out and no one changes them. New person over time thinks bulbs on is a fault so he never knew it was bulb out means fault. He thinks "everything is good no lights"


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## MotoGP1199 (Aug 11, 2014)

just the cowboy said:


> In systems like this, the problem is the bulbs burn out and no one changes them. New person over time thinks bulbs on is a fault so he never knew it was bulb out means fault. He thinks "everything is good no lights"


Yeah the fault light fixed it self, right ?


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## cuba_pete (Dec 8, 2011)

just the cowboy said:


> In systems like this, the problem is the bulbs burn out and no one changes them. New person over time thinks bulbs on is a fault so he never knew it was bulb out means fault. He thinks "everything is good no lights"


Nobody on our facilities shop has replaced any MCC lamps for over five years. They’re all burned out. The manager decided to contract out new equipment because he was told new lamps couldn’t be found...long story, sad ending for taxpayers.


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## Randy82 (Jan 25, 2021)

just the cowboy said:


> Nice catch. Yes it is because they can take a fault and keep running with one fault till they can empty a pour.
> Cowboy


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## Randy82 (Jan 25, 2021)

scameron81 said:


> If it’s a proper ungrounded system you should have ground indicator lights/ ground fault alarm to tell you there is a ground condition. In theory they are better but they can be quite dangerous. They are setup on the assumption that the ground will be addressed quickly and you don’t have to blow up your equipment when it fails.
> 
> Often times it isn’t and then you end up with what I call “double fault syndrome”. You have a ground on phase say A phase. Now your potential to ground is 480V so something else fails on B or C phase and two pieces of equipment blow up at once. It’s also bad for the breakers because they’re having to interrupt a phase to phase fault through a single pole of the breaker.
> 
> ...


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## Randy82 (Jan 25, 2021)

The thing I failed to mention is this is an old Chrysler plant, built back I believe in the 50-60’s. The services probably haven’t been upgraded in probably 10 years. Like I said earlier also, we aren’t allowed access to the MCC rooms.


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