# 120/240V 3 Phase delta. What is going on?



## wildleg (Apr 12, 2009)

did you check to see
- if the ground is loose
- if the point you though was ground was not a ground
- if their is ground monitoring (ungrounded meaning your measurements to ground were meaningless)
- if someone had played with the taps because of their peak (daily) loads ?

does this look better?:
310-30=280
142-30=112
156-30=126

curious why you didn't check the phase to phase


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## Bakerbro (Jul 31, 2013)

The phase to phase is all 240v. I am looking at it right now. I drove down to check it out once more. It is a three wire system with no neutral. Would you need a transformer with a center tapped nuetral to balance the voltage?


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## wildleg (Apr 12, 2009)

I can only guess that the previous tenant had only delta 3p or single phase 240 loads( if you aren't seeing any other trannies/panels). sounds like your friend is going to have to invest in some infrastructure to get 208Y120 (or whatever it is that he wants)


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## JW Splicer (Mar 15, 2014)

Was it a 240V delta that someone center tapped in a place other than the center? This doesn't make sense, are there lights in the place? Are they 120V? Receps? Where is the 310V coming from? no 120V anywhere?


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## A Little Short (Nov 11, 2010)

That sounds an awful lot like an ungrounded Delta.
Those readings to ground don't make sense otherwise.
Not that they make sense anyway because you would have nothing to measure to with no ground.

If you don't know from looking I would call the POCO and ask them to look at it.

If it were a Delta with high leg you readings would be more like:
A-G=120V
B-G=208V
C-G=120V

Phase to Phase on all would be 240V


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## Southeast Power (Jan 18, 2009)

Bakerbro said:


> So...I have a friend who just purchased a building in an industrial park. It is a pretty old building and he asked to come check out the electrical for him. So I go down and check it out and as I open the main disconnect I see the phasing tape Black, Orange, Blue. Right away I can "assume" 240v 3phase, but you know what assuming does. Never the less I begin to take a voltage reading. First, Aphase to ground, reading is 156V. Okay? Now I know Bphase is the bastard (or high leg as some would call it) phase so I do my check and as I suspected something or other, 310V. Finally I checked Cphase, and it had about 142v to ground.
> 
> Now I have been around 3phase systems quite a bit in my life, mostly 120/208v WYE and 277/480v WYE.
> 
> ...


It seems like the center tap on the one transformer is open. Possibly last, broken or stolen.
I doubt the ever ran it ungrounded. I see these systems every day, one one does that...
If it was actually corner grounded for some reason, one phase would, of course, read 0 to ground.
Either way, some work will be necessary before they can use this building.


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## ampman (Apr 2, 2009)

Could also be a bad transformer I've seen all kinds of weird voltage readings when a trans goes bad on a delta system call the poco and have them check their transformers


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## sparky278 (Apr 8, 2015)

checking your voltage to ground? you should be going to your neutral reference, possible that they did not bond the neutral and it is floating. I run into this when my guys check control voltage they go to ground instead of the neutral


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## varmit (Apr 19, 2009)

This sounds like a 240 volt ungrounded delta system. In many older buildings there would be two services from the utility: A 240 volt three phase delta for the equipment, and a 240/120 single phase service for lighting and 120 VAC loads.

Could there be another service somewhere else in the building? If there are other tenants in the building, the "lighting panel" could be in another tenants area.


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## A Little Short (Nov 11, 2010)

sparky278 said:


> checking your voltage to ground? you should be going to your neutral reference, possible that they did not bond the neutral and it is floating. I run into this when my guys check control voltage they go to ground instead of the neutral


OP says no neutral.
That's why most here are thinking it's an ungrounded system.


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## John (Jan 22, 2007)

Best thing to do is call the POCO and have them verify what it's supposed to be. Then go from there and fix it.
Looks to be corner grounded delta......with problems.


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## Bakerbro (Jul 31, 2013)

I finally got to take a closer look at everything. There is no neutral coming from the transformer outside. That being an over head three wire. No triplex. The only thing I was able to check was phase to phase and phase to ground. My friend tried calling the power company but the powerco in my area are a bunch of morons. "Duquesne light". 

We talked about it and he is wanting a whole updated service. 277/480v wye
Of course that's a lot of work for a while. 



I was kinda stumped on what the hell was goin on. I appreciate all the replies. They helped out a ton. I've never seen anything like that before. 
Thank you!


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