# I'm confused. Need some suggestion.



## hairdog (Aug 24, 2009)

I went to help one of my fellow journeyman today change out a transformer. The problem the customer said they were having was low voltage on B phase. Took voltage readings at the transformer and sure enough B phase had 25 volts coming out . Another issue was there was only 175 volts on on H1 coming from the high voltage panel. We discovered this is due to a faulty bus plug feeding the high voltage panel. 
We changed the transformer out with a brand new one. Made all the terminations and turned it back on and still have the same issue with the low voltage on B phase.

So we checked to make sure all terminations were correct again . All good there.

We checked to make sure X0 was grounded. Good there. 

Checked the Breaker feeding the primary with moving wires to another breaker. All good there. 

So I took and swapped B phase and C phase primary in the transformer To see if by chance we might have gotten a bad transformer. When we turned it on and check voltages the 25 volts showed up on A phase now. Now I'm really confused. How did the low voltage swap from B phase to A phase by swapping B phase and C phase? 

Could the the low voltage coming from the A phase at the bus plug Be causing the issue with the transformer? 

Here's the readings at the bus plug and tranformer.

Bus plug
A - 175 V
B - 277 v
C - 277 v

Transformer
Primary
A - 175 V 
B - 277 V
C - 277 V

Secondary
A - 95 V
B - 25 V
C - 120 V

Any suggestions would be greatly appreciated because I'm stumped.


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## MDShunk (Jan 7, 2007)

Fix your primary!!!


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## oldman (Mar 30, 2007)

MDShunk said:


> Fix your primary!!!


nah.....


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## william1978 (Sep 21, 2008)

MDShunk said:


> Fix your primary!!!


 I agree. Whatever the problem is it should fix all 3.


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## hairdog (Aug 24, 2009)

Thats what I was thinking . Everything that I did pointed at that. It's going to be a expensive fix. The bus plug is the old Federal Pacific's. I'm not sure You can even get them any more.


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## william1978 (Sep 21, 2008)

hairdog said:


> Thats what I was thinking . Everything that I did pointed at that. It's going to be a expensive fix. The bus plug is the old Federal Pacific's. I'm not sure You can even get them any more.


 You should be able to get it. It just might take some searching to find it though.


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## hairdog (Aug 24, 2009)

And a big check book.


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## william1978 (Sep 21, 2008)

hairdog said:


> And a big check book.


 That was a given when you said Federal Pacific. :laughing:


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## RePhase277 (Feb 5, 2008)

It may be on the POCO side. I can't really imagine that a bad connection would result in an open circuit voltage of 175, since no current is flowing and therefore no voltage drop. Sounds like a utility transformer problem.


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## hairdog (Aug 24, 2009)

That might be true but we checked the voltage of the bus plug right below the suspect one and All voltages were good.


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## william1978 (Sep 21, 2008)

InPhase277 said:


> It may be on the POCO side. I can't really imagine that a bad connection would result in an open circuit voltage of 175, since no current is flowing and therefore no voltage drop. Sounds like a utility transformer problem.


 It is posible that it could be a loss connection. Just took a floor over from another foreman a few weeks back and they had already wired the AHU's and the HVAC guys were ready to energize them last week so we cut the on to find out that on had phase A had 25v phase b had 286 phase had 25v so we shut the psnel down to find out that when the guy that put in the correct OCP only had the screw on B phase tight. So I thighten phase A and C and it fixed the problem.


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## Toronto Sparky (Apr 12, 2009)

May be a phase out on the primary at the street transformer.
But more than likely it's the bus plug burning on the bus.


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## azsly1 (Nov 12, 2008)

check the bus itself. not the plug, the actual bus. there could be a bad splice....


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## oldman (Mar 30, 2007)

i love that the transformer was already changed...how happy is that customer going to be?


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## hairdog (Aug 24, 2009)

The transformer was changed out at there Maintanence mans direction. It was not our call. Only after did we find the issue witht the bus plug.


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## Zog (Apr 15, 2009)

hairdog said:


> The transformer was changed out at there Maintanence mans direction. It was not our call. Only after did we find the issue witht the bus plug.


I would think someone would actually test the transformer before changing it.


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