# Phase to N Votage at Booster Ouput?



## Cletis (Aug 20, 2010)

*208*

I'll guess 208? delta? high leg?


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## swimmer (Mar 19, 2011)

Cletis said:


> I'll guess 208? delta? high leg?


So Cletis weighs in with 208V. Gnarley webpage dude!
Only half my kids will die in my fire trap house so I'll hold off on calling you for now. Maybe go with some budget guy.

To Clarify, Phase 1, Phase 2, Phase 3 and Neutral are coming from a Typical 208 / 120 Y panel.

No deltas, high legs, corner grounds, open phases... etc.. etc...


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## Big John (May 23, 2010)

You'd read 152V AØ-N or something close.

-John


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## swimmer (Mar 19, 2011)

Big John said:


> You'd read 152V AØ-N or something close.
> 
> -John


Thanks John
152V = 120V + (240V - 208V)
Have you actually seen this on a transformer output?


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## Big John (May 23, 2010)

swimmer said:


> ...Do you have any idea why 152V?


 If it helps to envision it: Erase the winding between AØ and BØ; the winding that's left on AØ is self-inducing; the voltage on that phase is boosting _itself _and it will be higher to any other point you measure on that transformer: L-L, L-N, L-G, it doesn't matter.

-John


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## frenchelectrican (Mar 15, 2007)

I came up 136 volts due you have 32 volt B/B to boost from 208 to 240 volts so line to netural will be about 136 ( 120 + 16 = 136 ) 

But that answer will varies a bit depending on the B/B winding connection it may be higher than that.

So if you have any 120 volt load you may want to double check it before you make a good engerizeation to the equiment you want to be on.

Merci,
Marc


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## Southeast Power (Jan 18, 2009)

swimmer said:


> Thanks John
> 152V = 120V + (240V - 208V)
> Have you actually seen this on a transformer output?


Are you considering using it phase to neutral or it this an experiment?


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## Big John (May 23, 2010)

frenchelectrican said:


> I came up 136 volts due you have 32 volt B/B to boost from 208 to 240 volts so line to netural will be about 136 ( 120 + 16 = 136 )...


 I do know that B phase voltage-to-neutral will not change if wired as in that diagram, so I figure that all the boost has to be on one single phase. 

I'd actually have to wire one up to confirm it though.

-John


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## swimmer (Mar 19, 2011)

jrannis said:


> Are you considering using it phase to neutral or it this an experiment?



I need to run a circuit from a panel to a chiller.
I measured the input to the 208 / 120 3-phase panel at 196V / 113V.
The equipment tag on the chiller says 208 - 230 / 115 and is a 4 wire plug. Blk, Red, Wht, Grn

If I boost 196V 10% to 215V then I am concerned that the unknown output leg will be high enough to damage the digital stuff in the chiller. I don't know which wire (blk or red or both) is used by the digital stuff.

I used 208V / 120V to 240V in my question because it would be familiar to more people. I could then scale it back to 196V / 113V after I understood how it worked.


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## swimmer (Mar 19, 2011)

swimmer said:


> I measured the input to the 208 / 120 3-phase panel at 196V / 113V.


Here are some things I know about this low voltage.
1. This panel and 2 other panels that read low like this are about 300 ft away from the main electrical room from which they are fed.

2. Two of these low reading panels are fed by 4'x'4'x 2' transformers mounted 15' high on the wall. I don't know the input voltage to the transformer but it is fed by 3/4 EMT which makes me think it is a high voltage / low current feed. The output from the transformer is 3 1/0 wires in 2" EMT.


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## Big John (May 23, 2010)

Swimmer, it sounds like you've already got a solution, but have you looked to see if the feeder xfrmrs have taps you could bump up?

-John


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## micromind (Aug 11, 2007)

swimmer said:


> Here are some things I know about this low voltage.
> 1. This panel and 2 other panels that read low like this are about 300 ft away from the main electrical room from which they are fed.
> 
> 2. Two of these low reading panels are fed by 4'x'4'x 2' transformers mounted 15' high on the wall. I don't know the input voltage to the transformer but it is fed by 3/4 EMT which makes me think it is a high voltage / low current feed. The output from the transformer is 3 1/0 wires in 2" EMT.


Those transformers are either 30 or 45 KVA. 480 (most likely delta) to 120/208 wye.

They most likely have taps inside, my solution would be to change the taps first, then see if you even need the B/B transformers. 

Is the voltage always this low, or only at certain times of the day?


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## micromind (Aug 11, 2007)

Big John said:


> Swimmer, it sounds like you've already got a solution, but have you looked to see if the feeder xfrmrs have taps you could bump up?
> 
> -John


Rats!!

2 minutes late......

Lol.


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## Big John (May 23, 2010)

Beat ya. 









-John


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## swimmer (Mar 19, 2011)

micromind said:


> Is the voltage always this low, or only at certain times of the day?


I don't know yet. I'm monitoring over the weekend and a few days into next week with one of those meters that holds on the highest voltage.


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## swimmer (Mar 19, 2011)

Big John said:


> Swimmer, it sounds like you've already got a solution, but have you looked to see if the feeder xfrmrs have taps you could bump up?
> 
> -John


I'll bring my opera glasses or get up on a ladder and see what I can find out about those transformers when I go in next week to retrieve my "recording" meter.


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## swimmer (Mar 19, 2011)

Big John said:


> Swimmer, it sounds like you've already got a solution, but have you looked to see if the feeder xfrmrs have taps you could bump up?
> 
> -John


John, I don't really have a solution yet but I'm beginning to understand my choices. 

This panel supplies 7 cash register stations and another low reading panel supplies the deli food processing equipment. There are absolutely no complaints about high equipment failure rates so I'm leaning toward just installing the circuit with no transformer.


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## Big John (May 23, 2010)

I don't know how big this chiller is, but I'd be a little worried about added voltage drop. 

NEMA specs allow down to 108 volts for a 120V circuit and 187 for a 208V circuit, but that is different from saying it's a good idea to run equipment that low.

-John


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## swimmer (Mar 19, 2011)

Big John said:


> I don't know how big this chiller is, but I'd be a little worried about added voltage drop.
> 
> NEMA specs allow down to 108 volts for a 120V circuit and 187 for a 208V circuit, but that is different from saying it's a good idea to run equipment that low.
> 
> -John


You definitely have a point there.
The other consideration is that I don't want to find out the hard way why these were tapped low. I'll know more after I retrieve my meter. I should get the high voltage for both high and low loading.


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## frenchelectrican (Mar 15, 2007)

I will post the B/B diagram and I will fill you in a second after I post it. something did came up in my mind so better get this straighten out before something go heck ( WTFreak ) 













If you look at diagram C et D the C you will kick up 16 volts while diagram D will kick up 32 volts however there one thing John did hit the nail on one phase ( L2 ) the 120 volt will NOT affect but the other leg it will affect so I will have to post the revised rating so it will be anywhere from 136 to 156 volts from L1 to Netural.

So that can raise a new issue if you do plan to use the B/B avce 120 volt loads so pay attetion to it.

I did ran a little experment real quick and did see a minor blunder so better get this taken care of it right away before someone else get arse bitted from this one.

Merci,
Marc

If you can get 12/24 verison you should be little safer but use the judgement call after you do the system check first to see how much it drop.


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## swimmer (Mar 19, 2011)

frenchelectrican said:


> I came up 136 volts due you have 32 volt B/B to boost from 208 to 240 volts so line to netural will be about 136 ( 120 + 16 = 136 )



An application engineer at Jefferson Transformer said "around 140V"
So it appears that French Electrician is looking at it the right way.


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## frenchelectrican (Mar 15, 2007)

I just may hit the right spot there however before you make final connection you may want to double check with your voltmeter to verify the voltage on each " phase " and may have to shift any 120 volts on correct one.

Also it will be wise idea to put a warning sign that it have B/B so they will know the line to netural voltage will not be correct if they did tapped in wrong spot.

Merci,
Marc


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