# Transformer strange configuration



## LGLS (Nov 10, 2007)

Corner grounded open delta?


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## FL JW (Jul 16, 2021)

LGLS said:


> Corner grounded open delta?


Maybe. But what would be the application? The two phases were feeding a disconnect that had at one point, presumably, been feeding equipment. There was no neutral in the raceway

Edit: on second thought probably not. The service is 120/208


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## gpop (May 14, 2018)

It's a buck and boost wired for 208 input to 240 output


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## FL JW (Jul 16, 2021)

gpop said:


> It's a buck and boost wired for 208 input to 240 output


That was my first thought, but the difference in voltage between the two phases really confused me. Is that typical for buck boosters?


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## gpop (May 14, 2018)

Yep 32v gain on one leg no neutral


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## splatz (May 23, 2015)

gpop said:


> It's a buck and boost wired for 208 input to 240 output


The instructions are surprisingly easy to find, nice work Square D / SE
2S46F - Low voltage transformer, encapsulated buck boost, 1 phase, 2kVA, 120x240V primary, 16/32V secondary, Type 3R | Schneider Electric USA
https://download.schneider-electric..._Name=39000-322-01.pdf&p_Doc_Ref=39000-322-01


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## FL JW (Jul 16, 2021)

splatz said:


> The instructions are surprisingly easy to find, nice work Square D / SE
> 2S46F - Low voltage transformer, encapsulated buck boost, 1 phase, 2kVA, 120x240V primary, 16/32V secondary, Type 3R | Schneider Electric USA
> https://download.schneider-electric..._Name=39000-322-01.pdf&p_Doc_Ref=39000-322-01
> 
> View attachment 165199


Awesome. That's exactly how it's wired. Why would you need it to do that? I'm not familiar with any application where that would be needed


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## Almost Retired (Sep 14, 2021)

FL JW said:


> Awesome. That's exactly how it's wired. Why would you need it to do that? I'm not familiar with any application where that would be needed


240V instead of 208V somethings wont interchange voltage


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## FL JW (Jul 16, 2021)

Almost Retired said:


> 240V instead of 208V somethings wont interchange voltage


Yeah, but why would 1 leg be 120v and the other be 150?


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## LGLS (Nov 10, 2007)

FL JW said:


> Yeah, but why would 1 leg be 120v and the other be 150?


Because you’re measuring those legs to neutral, and the whole point of the buck& boost is to get 240 V , for a load that does not require a neutral. But if you did need a neutral at least you had that 120 V leg for control circuit.


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## FL JW (Jul 16, 2021)

LGLS said:


> Because you’re measuring those legs to neutral, and the whole point of the buck& boost is to get 240 V , for a load that does not require a neutral. But if you did need a neutral at least you had that 120 V leg for control circuit.


I hate to be a pedant, but there is no neutral. It's just 2 hots and a ground. Does that make a difference?


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## LGLS (Nov 10, 2007)

FL JW said:


> I hate to be a pedant, but there is no neutral. It's just 2 hots and a ground. Does that make a difference?


NeverMind, need more Java here. You’re getting those voltages to ground, yes?


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## micromind (Aug 11, 2007)

FL JW said:


> Yeah, but why would 1 leg be 120v and the other be 150?


One leg goes straight through, the other leg is boosted up by 32 volts. 

There is no neutral, in fact there cannot be a neutral because one leg is boosted up.


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## gpop (May 14, 2018)

Look at the wiring diagram. The low voltage leg is also the high voltage leg on one side.

The other low voltage leg uses the transformer so it gets a 32v kick


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## FL JW (Jul 16, 2021)

micromind said:


> One leg goes straight through, the other leg is boosted up by 32 volts.
> 
> There is no neutral, in fact there cannot be a neutral because one leg is boosted up.


This goes back to the original question. If there's no neutral, how would you use if for a control circuit, and then what's the point of the higher voltage leg? Why not use a wye-delta 1:1 transformer? Money?


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## Almost Retired (Sep 14, 2021)

it was not for a control cct
it was for a *240V* _power_ cct
a cct that did not need or want a neutral
such as a 240V motor


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## FL JW (Jul 16, 2021)

Almost Retired said:


> it was not for a control cct
> it was for a *240V* _power_ cct
> a cct that did not need or want a neutral
> such as a 240V motor


LGLS brought up control circuits

Is it cheaper to throw in a buck booster than a wye-delta transformer? Idk, it just seems like kind of a shifty solution


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## gpop (May 14, 2018)

I install a lot of little liftstation pumps that require 240 and some of the places only have 208 3 phase.
To expensive to go 3 phase, I want a standardized pump so I'm not using 120v which leaves me with a buck and boost as a cheap option 

It works and I've never seen one fail so what's the problem


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## Almost Retired (Sep 14, 2021)

FL JW said:


> LGLS brought up control circuits
> 
> Is it cheaper to throw in a buck booster than a wye-delta transformer? Idk, it just seems like kind of a shifty solution



_*240V*_ and *NOT* 208V is the whole point of it

buck boost transformers can be used at more than their kva rating because of how they are hooked up
so yes this is the most cost effective way to go (not meaning cheap as in wont hold up)
what amp breaker is feeding the txr ?

the txr tag shows 2kva
at 240V that is 8.3 amps
the feed breaker is undoubtedly higher than that


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## FL JW (Jul 16, 2021)

Almost Retired said:


> _*240V*_ and *NOT* 208V is the whole point of it
> 
> buck boost transformers can be used at more than their kva rating because of how they are hooked up
> so yes this is the most cost effective way to go (not meaning cheap as in wont hold up)
> ...


50 amps


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## Almost Retired (Sep 14, 2021)

FL JW said:


> 50 amps


there ya go

ya wanna buy a 50 amp transformer with a lot of taps ? .... or a simple 8 amp txr ?
do you wanna make space for a 50a or a 8 a ?

go here








Buck Boost Transformers - Jefferson Electric


Back to all products Products 50 VA – 10 kVA Applications For correcting voltage drop, landscape lighting, low voltage lighting, international voltage adaptation and motor applications Note: Buck-boost transformers do not compensate for fluctuating line voltages Information sheet...




jeffersonelectric.com





and do some browsing. as an electrician this will be helpful to you in the future


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## micromind (Aug 11, 2007)

FL JW said:


> This goes back to the original question. If there's no neutral, how would you use if for a control circuit, and then what's the point of the higher voltage leg? Why not use a wye-delta 1:1 transformer? Money?


It's not a control circuit. Its purpose is to raise the existing 208 to 240. Single phase 2 wire, no neutral. 

I've installed a pretty fair number of these, it's the easiest and least expensive way to get 240 from a 208 system.


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## LGLS (Nov 10, 2007)

micromind said:


> It's not a control circuit. Its purpose is to raise the existing 208 to 240. Single phase 2 wire, no neutral.
> 
> I've installed a pretty fair number of these, it's the easiest and least expensive way to get 240 from a 208 system.


Man the arguments we used to have with the Xerox guys back in the 90s… Their machine was rated at 240v but all over the city they ran just fine on 208, except when they didn’t and the technicians, for whatever reason (since most Xerox photo copy as were up until then least) that couldn’t figure out what the real problem was with always blame low-voltage and try to kick it to the building not supplying enough power.


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## oldsparky52 (Feb 25, 2020)

FL JW said:


> That was my first thought, but the difference in voltage between the two phases really confused me. Is that typical for buck boosters?


Yes, it is typical. Each leg starts at 120V to ground, then one leg gets boosted farther away from the other leg to get 240V. The leg not boosted stays 120 (in reference to ground), the added voltage shows up on the other leg to give you the 240, so that boosted leg also goes up in reference to ground.


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## oldsparky52 (Feb 25, 2020)

I am going to talk above my education level here, so be kind when you correct me. 

The voltage is increased in reference to the 208 vector which means if you increase the voltage on one leg by 32 volts, the increase in the voltage to ground (that is properly bonded to the Wye secondary neutral) would be less than 32 volts.

I'm not sure what that voltage would be.


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## gpop (May 14, 2018)

oldsparky52 said:


> I am going to talk above my education level here, so be kind when you correct me.
> 
> The voltage is increased in reference to the 208 vector which means if you increase the voltage on one leg by 32 volts, the increase in the voltage to ground (that is properly bonded to the Wye secondary neutral) would be less than 32 volts.
> 
> I'm not sure but my guess it would be 32/1.732. Please someone that knows comment on this. Thanks.


No secondary neutral but you can read the primary neutral on one leg which is effectively the same primary and secondary as it's the same wire.

The other leg will show 120 + 32 in reference to ground which is a quick and easy way to tell you have a boost transformer somewhere in the circuit.


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## oldsparky52 (Feb 25, 2020)

gpop said:


> *The other leg will show 120 + 32 in reference to ground* which is a quick and easy way to tell you have a boost transformer somewhere in the circuit.


I think this is incorrect. The boost would be in reference to the 208V (vector, plane, line, ???). That would extend the vector by 32 volts but the neutral is not on that line, it's off to the side since the 208 is from a 3-phase source.


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## LGLS (Nov 10, 2007)

Almost Retired said:


> _*240V*_ and *NOT* 208V is the whole point of it
> 
> buck boost transformers can be used at more than their kva rating because of how they are hooked up
> so yes this is the most cost effective way to go (not meaning cheap as in wont hold up)
> ...


Why can’t one grab the neutral from the primary side, and run a control circuit at 120v between N and H1 or H4?


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## gpop (May 14, 2018)

oldsparky52 said:


> I think this is incorrect. The boost would be in reference to the 208V (vector, plane, line, ???). That would extend the vector by 32 volts but the neutral is not on that line, it's off to the side since the 208 is from a 3-phase source.


It would be interesting to see this on a scope.


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## oldsparky52 (Feb 25, 2020)

My drawing program is on a laptop I've not used in years. I tried to turn it on and I think the battery needs to be replaced. I could draw it up to scale and get the answer to what the yellow voltage would be (from the boosted end to neutral).


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## oldsparky52 (Feb 25, 2020)

LGLS said:


> Why can’t one grab the neutral from the primary side, and run a control circuit at 120v between N and H1 or H4?


Who said you could not?


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## oldsparky52 (Feb 25, 2020)

Duplicated post


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## gpop (May 14, 2018)

oldsparky52 said:


> Who said you could not?


H1 you could 

H4 would not be a good idea and don't ask how i know that.


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## CMP (Oct 30, 2019)

For your yellow line measurment, the OP posted his measured result of 150V. But I would note that his input voltage was slightly high judging by his 123V leg reading.


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## oldsparky52 (Feb 25, 2020)

gpop said:


> H1 you could
> 
> H4 would not be a good idea and don't ask how i know that.


H1 and H4 are both fed from the 208 source and are both 120V to neutral. X4 is a different story.


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## oldsparky52 (Feb 25, 2020)

CMP said:


> For your yellow line measurment, the OP posted his measured result of 150V. But I would note that his input voltage was slightly high judging by his 123V leg reading.


Yea I was looking at that a bit more.

123.9 B to Gr
249 phase to phase (after the transformer)
150 A to Gr

So we have to make an assumption that the unboosted A phase voltage to ground is the same as B phase voltage to ground for our calculations. 

123.9*1.732=214.6 unboosted phase to phase voltage

249-214.6=34.4 "boost" in phase to phase voltage.

123.9+34.4=158.3 This would be the voltage to ground if the voltage added exactly the same for the phase to phase and the phase to ground. But the phase to ground is 150V, 8V short.


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## oldsparky52 (Feb 25, 2020)

oldsparky52 said:


> My drawing program is on a laptop I've not used in years. I tried to turn it on and I think the battery needs to be replaced. I could draw it up to scale and get the answer to what the yellow voltage would be (from the boosted end to neutral).
> 
> View attachment 165219


IDK, is there a phase shift with the boost transformer? Does that boosted section need to be drawn at a different angle that it is?


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## LGLS (Nov 10, 2007)

oldsparky52 said:


> IDK, is there a phase shift with the boost transformer? Does that boosted section need to be drawn at a different angle that it is?


No but it’s vector is extended further. You might say it’s going off on a tangent.


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## CMP (Oct 30, 2019)

I don’t think you can accurately compute the result, by estimating the L1 to L2 input. There could also bee some small differences between readings to ground versus to the true neutral, depending on the bonding connections. 

I think that the measured 150V is close enough enough to prove gpop’s conclusions, that you don’t want to use that extended phase to tap off a 120V circuit.


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## CMP (Oct 30, 2019)

When I use buck/ boost transformers or standard 4 winding units 480/240- 240/120 for rotary phase converters. I split the secondary winding to buck/boost half of the amount on each phase leg, to give me a more balanced output to ground on the RPC output.

It’s not any connection you will find in any manufacturers literature, but I have used it many times and it produces a more balanced output on the RPC. Have also used it on a 3 phase auto transformer testing supply, to derive 3 different outputs from one input voltage.


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## micromind (Aug 11, 2007)

CMP said:


> When I use buck/ boost transformers or standard 4 winding units 480/240- 240/120 for rotary phase converters. I split the secondary winding to buck/boost half of the amount on each phase leg, to give me a more balanced output to ground on the RPC output.
> 
> It’s not any connection you will find in any manufacturers literature, but I have used it many times and it produces a more balanced output on the RPC. Have also used it on a 3 phase auto transformer testing supply, to derive 3 different outputs from one input voltage.


I do the same thing. 

If possible, I'll buck or boost each leg the same amount.


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## splatz (May 23, 2015)

oldsparky52 said:


> My drawing program is on a laptop I've not used in years. I tried to turn it on and I think the battery needs to be replaced. I could draw it up to scale and get the answer to what the yellow voltage would be (from the boosted end to neutral).
> View attachment 165219


Note that the acute angle between the red and the purple is 30 degrees. (The sum of the angles inside a triangle is 180 degrees, 120 + x + x = 180, so x = 30.)

Therefore the obtuse angle between the red and the purple is 150 degrees, since the obtuse and the acute must add up to 180 degrees.

Now you can use the law of cosines to solve for the length of the yellow segment, it comes to 148.58, which is pretty close to the OP's voltage reading.


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## CMP (Oct 30, 2019)

I posted this earlier as a sample diagram, but ill park it here again, as an example of a balanced buck/boost connection.


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## LGLS (Nov 10, 2007)

Ugly’s eat your heart out.


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## Almost Retired (Sep 14, 2021)

LGLS said:


> Why can’t one grab the neutral from the primary side, and run a control circuit at 120v between N and H1 or H4?


didnt say you couldnt change it to that
said it was not currently set up for that
apples and oranges, and muddy water for the OP who is having trouble already without adding another variable
i follow the KISS rule when trying to help ppl


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## oldsparky52 (Feb 25, 2020)

splatz said:


> Note that the acute angle between the red and the purple is 30 degrees. (The sum of the angles inside a triangle is 180 degrees, 120 + x + x = 180, so x = 30.)
> 
> Therefore the obtuse angle between the red and the purple is 150 degrees, since the obtuse and the acute must add up to 180 degrees.
> 
> ...


Thanks Buddy! I was hoping you would come by and show the math.


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## FL JW (Jul 16, 2021)

CMP said:


> When I use buck/ boost transformers or standard 4 winding units 480/240- 240/120 for rotary phase converters. I split the secondary winding to buck/boost half of the amount on each phase leg, to give me a more balanced output to ground on the RPC output.
> 
> It’s not any connection you will find in any manufacturers literature, but I have used it many times and it produces a more balanced output on the RPC. Have also used it on a 3 phase auto transformer testing supply, to derive 3 different outputs from one input voltage.


Thanks for this post. If no one else has anything to say to the contrary, doing it like this would probably make me sleep better


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## CMP (Oct 30, 2019)

A small point to make when measuring or calculating standard buck/ boost transformer voltage values. Standard units have a 120/240 primary winding, if you feed it 208V in order to boost voltage, thats 15% less than it was wound for. So the output voltage will be less as well.

In the case of a boost of a 32V unit from 208V supply, the boost voltage will be more like 32V / 1.15 = 27.8V vs 32V on the tag. If you split the secondary as suggested earlier, that will result in adding 13.9V to each leg, as measured to ground. 120V + 13.9V = 133.9V on each leg, so no 120V loads to be connected.

There will likely be some small differences since small transformers 1KVA and less usually have a compensation winding coil added in.


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