# Voltage from H to X?



## Tom45acp (Sep 6, 2011)

Since it is likely that you're feeding the transformer from a grounded system, the voltage H to X should be 277 volts.

I think that there is a phase shift when you pass thru a transformer so you should measure more than 277 volts from one of the 277 lines to one of the 120 lines. I've never actually measured this, but I'm going to next time I get a chance. 

If you want to put both voltages to switches in the same box, use a box partition.


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## Fibes (Feb 18, 2010)

BorderlineSane said:


> This question was a result of an argument between a friend and I over having a 120v switch and a 277v switch in the same box. It has recently become a 2 part question.
> 
> 1) What would the voltage be if you measured from the H to any of the X's in a 480 to 208/120 transformer?


 It can be as much as 380 volts depending on the combination of phases being read



BorderlineSane said:


> 2) A different friend and i measured from the C phase of a 480 panel to the 3 phases of a 120/208 panel that was fed from the 480 panel we were testing from. Our measurements came back as 7v, 6v, 7v. We are both baffled by the measurements. i personally think he forgot to turn the Main breaker on in the 120/208 panel but he swears he had it on.


I think something was off.


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## BBQ (Nov 16, 2010)

Tom45acp said:


> Since it is likely that you're feeding the transformer from a grounded system, the voltage H to X should be 277 volts.


Any 'H' to 'X0' will show 277 volts.

But Any H to X1, X2 or X3 will read a voltage that will be dependent on if you are reading between the same phase or opposing phases.

It can be figured out, I just do not know how.


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## Lone Crapshooter (Nov 8, 2008)

Would the exact voltage be dependant on the transformer polairty and the angular displacement of the phases?
LC


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## l0sts0ul (May 7, 2011)

I don't want to e a jerk but who cares? 


Ultimately it's based on the turn ratio and the actual input voltage on each phase. You would have to use a phaser diagram to calculate it and figure out all 9 possible phaser calculations to know what h1,2,3 and x1,2,3 would be respectively.

Your question is irrelevant because you don't need to ever know that. It's a pointless argue ment. 

Yes, divide the box, label accordingly and move on.


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## Fibes (Feb 18, 2010)

l0sts0ul said:


> Your question is irrelevant because you don't need to ever know that.


 
Exactly how do you know the OP will never need to know that?


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## l0sts0ul (May 7, 2011)

Why would you? You need the input

Voltage. And output voltage. And if you have 1 you can determine the other and meter to confirm. There is not a case you can give me that would tell me you need to know the phasoral angle and lagging current values on the input and output of the transformer In empirical comparison. It is values that are irrelevant.


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## Fibes (Feb 18, 2010)

l0sts0ul said:


> Why would you?


Why wouldn't you? Even if the OP will never need it for practical application is that a reason to turn off the desire to learn or the quest for knowledge?


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## l0sts0ul (May 7, 2011)

Ok 


If you were working for me and you called me to tell me you spent time arguing about this an wasting company money on something as irrelevant as this I would tell you to take to a day off without pay to figure it out. 

If you called me or told me you metered it, I would say great, but this is something that does not better your knowledge or wisdom or expertise in the trade. Tell me where this newfound knowledge would be applied??

How does it make you a better electrician to know this?


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## hardworkingstiff (Jan 22, 2007)

l0sts0ul said:


> Ok
> 
> 
> If you were working for me and you called me to tell me you spent time arguing about this an wasting company money on something as irrelevant as this I would tell you to take to a day off without pay to figure it out.
> ...


I understand the viewpoint stated and you are correct about not spending company time on this. But you are just as wrong to trivialize someone that would want to know what the voltages would be and why.

Personally, I would like to know how to calculate it if someone with knowledge and time would be willing to post the information.


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## l0sts0ul (May 7, 2011)

I'm not trivializing it. I'm simply stating that the need to know this not useful in the trade. 

I want to know myself and when I get back to te office I will calculate it and show my data.


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## Fibes (Feb 18, 2010)

l0sts0ul said:


> Ok
> 
> 
> If you were working for me and you called me to tell me you spent time arguing about this an wasting company money on something as irrelevant as this I would tell you to take to a day off without pay to figure it out.


 Well then I wouldn't call you.



l0sts0ul said:


> If you called me or told me you metered it, I would say great, but this is something that does not better your knowledge or wisdom or expertise in the trade. Tell me where this newfound knowledge would be applied??


Here on this forum that you are wasting your time on.



l0sts0ul said:


> How does it make you a better electrician to know this?


Like all other calculations that are not used everyday.


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## Fibes (Feb 18, 2010)

l0sts0ul said:


> I want to know myself and when I get back to te office I will calculate it and show my data.


Let me help you out, there was a couple of good disscussions at Mike Holts forum, click here


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## BBQ (Nov 16, 2010)

l0sts0ul said:


> I don't want to e a jerk but who cares?
> 
> 
> Ultimately it's based on the turn ratio and the actual input voltage on each phase. You would have to use a phaser diagram to calculate it and figure out all 9 possible phaser calculations to know what h1,2,3 and x1,2,3 would be respectively.
> ...


What if I actually want to know if I need a divider or not?


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## l0sts0ul (May 7, 2011)

2 different voltages in the same box requires a divider in CEC. 

I'm over the discussion about the voltages.


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