# Help on Xmfr Question



## RubyTuesday (Oct 19, 2014)

So I'm having some trouble trying to understand this question in my home work so I redrew it and tried to solve it to the best of my ability and I was wondering if I could get some input on it:










It was a diagram of the set of coils on the left and the round thing on the right and I was asked to connect the leads on the transformer. Is that object on the right also being considered an additional set of coils. I noticed since the source voltage is 480 V and the Primary is also 480 V I went ahead and connected the two sets of single phase transformers(at least that's what I think they are depicting), in parallel so that the voltages would not be additive. I also did the same with the secondary side since the load V is 120 V and the secondary coil is 120 V. If I am wrong in any way I would appreciate some guidance. Thanks.


----------



## Big John (May 23, 2010)

Well, seeing as how an oval with transformer notations isn't a recognized symbol, it makes it kinda hard to guess. Shame on whoever drew that nonsense for you.

I agree, it looks like two parallel 480:120V transformers. But that'd be a pretty unusual setup. What's the context of the question?


----------



## RubyTuesday (Oct 19, 2014)

ok well here goes the original diagram









It's basically just asking me to connect the leads. But I hadn't even seen that object in my textbook, so it's throwing me off.


----------



## emtnut (Mar 1, 2015)

Your first diagram ... you didn't have the Tx's in series OR parallel ...

Given that 480 is high , at it shows 120 low ... I'd say you should wire them in parallel .


----------



## AK_sparky (Aug 13, 2013)

That is a really weird diagram. I'm not sure what that is supposed to be.

But for starters, your first diagram only shows one 480v line connected.


----------



## mitch65 (Mar 26, 2015)

I would ignore the oval POS if there is no description of it and connect the transformer to the load.
As my 1st year code instructor always said: Reread the question.


----------



## telsa (May 22, 2015)

BTW, the convention is that 480 VAC is hot to hot; H1 to H2...

The 120 VAC is hot to neutral; X1 to *Xo*.

Admittedly you'll only see Xo with 3 phase transformers -- but, then again, you'll only see 480 VAC in 3-phase systems.

The connections in the OP scribble are way off.

Connect H1 and H2 to the 'rails' running across the top.

Connect X1 and X2 to the 'rails' running across the bottom... strictly speaking one might toss in a grounded connection to the bottom 'rail' -- as we don't wire ungrounded 120VAC circuits in this hemisphere.

No-one can figure out what the elliptical bubble means.

It's not a transformer, nor a capacitor, nor a motor,...


----------



## Big John (May 23, 2010)

I found the symbol on the right:


----------



## chrisfnl (Sep 13, 2010)

telsa said:


> strictly speaking one might toss in a grounded connection to the bottom 'rail' -- as we don't wire ungrounded 120VAC circuits in this hemisphere.


You've got a little something brown on your nose 

Though for what it's worth, we absolutely run ungrounded 120vac, old fashioned razor outlets are the most common example (120:120 isolation transformers) but high reliability industrial controls are another common example, should have ground detection included but not always...

Have come across the issue before where it was a 120 system we "thought" should be grounded, but drawings didn't show a ground on the xfmr, and there was a note specifying "ungrounded secondary".

Short story, don't assume and add stuff, follow the drawings.

Unless they're as crappy as what's above, then consult with designer.


----------



## telsa (May 22, 2015)

chrisfnl said:


> You've got a little something brown on your nose
> 
> Though for what it's worth, we absolutely run ungrounded 120vac, old fashioned razor outlets are the most common example (120:120 isolation transformers) but high reliability industrial controls are another common example, should have ground detection included but not always...
> 
> ...


You sensitive -- and ever polite -- Canadians. :whistling2:

Now you've REALLY corn fused the OP.


----------



## micromind (Aug 11, 2007)

RubyTuesday said:


> ok well here goes the original diagram
> 
> 
> 
> ...


This is 2 diagrams of the same transformer. The one on the left shows the polarity of the windings and the one on the right shows how they're marked on the can. 

If all you're doing is reducing the voltage from 480 to 120, then polarity doesn't matter. Apply 480 to H1 and H2 and you'll have 120 at X1 and X2. 

If the 120 needs to be grounded, simply ground either X1 or X2, it doesn't matter which one.


----------



## RubyTuesday (Oct 19, 2014)

AK_sparky said:


> But for starters, your first diagram only shows one 480v line connected.


:thumbsup: that's right, thanks, I'll extend the H2 line to the top line.


----------



## RubyTuesday (Oct 19, 2014)

emtnut said:


> Your first diagram ... you didn't have the Tx's in series OR parallel ...
> 
> Given that 480 is high , at it shows 120 low ... I'd say you should wire them in parallel .


I thought I had it wired up in parallel, I made a junction between H1 on the left and H1 on the right, and the same with H2, and the X1's and X2's. If it were to be series I would have wired it from left to right, H1 to one source line, H2 to the other H1, and the other H2 to the other source line.


----------



## RubyTuesday (Oct 19, 2014)

telsa said:


> BTW, the convention is that 480 VAC is hot to hot; H1 to H2...
> 
> The 120 VAC is hot to neutral; X1 to *Xo*.
> 
> Admittedly you'll only see Xo with 3 phase transformers -- but, then again, you'll only see 480 VAC in 3-phase systems.


Well, in our book it says if you connect 2 single phase coils in series and pull from that midpoint you can get a neutral.


----------



## RubyTuesday (Oct 19, 2014)

micromind said:


> This is 2 diagrams of the same transformer. The one on the left shows the polarity of the windings and the one on the right shows how they're marked on the can.


Yeah, that's definitely a possibility. Thanks


----------



## telsa (May 22, 2015)

RubyTuesday said:


> Well, in our book it says if you connect 2 single phase coils in series and pull from that midpoint you can get a neutral.


You are describing the classic center-tapped neutral... it gets grounded, of course.

Center-tapped transformers are used all over -- especially to include battery chargers.

Check one out some time.

Center-tapping 120VAC gives 60VAC -- which is then ~5:1 transformed to 12VDC.

( Actually, these are designed to hit ~13.8VDC. )

Such schemes are ubiquitous as Services for residential across America.


----------

