Buck/Boost Transformers

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dnbob

Senior Member
Location
Rochester, MN
Has anyone failed an inspection by using black, red, blue, on both a 120/208 3 phase system, and also on a 120/230 volt 3 phase system with a buck/boost transformer? 210.5 says we need to identify systems supplied from more than one nominal voltage. Isn't 208 & 230 still the same nominal voltage?
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
Wow ! You are going to send me back to my books. I have often used buck/boost to obtain 230 from a 208 system but did not think you could derive a full 230/120 system by buck & boost.
In answer to your question, I have never seen a rejection for identification of the secondary of a buck and boost, but the installs I have seen have been simple single pieces of equipment.
Unless you are encountering an installation where "orange" marking is required, such as a panel board, the 210.5 requirement does no specify color coding must be used, just means of identification.
Can you provide more detail ?
 

GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
Wow ! You are going to send me back to my books. I have often used buck/boost to obtain 230 from a 208 system but did not think you could derive a full 230/120 system by buck & boost.
In answer to your question, I have never seen a rejection for identification of the secondary of a buck and boost, but the installs I have seen have been simple single pieces of equipment.
Unless you are encountering an installation where "orange" marking is required, such as a panel board, the 210.5 requirement does no specify color coding must be used, just means of identification.
Can you provide more detail ?

A "three phase 120/230 volt system" using buck/boost transformers would have to provide one set of three line terminals for wye connected loads and a second set of line terminals for delta connected loads. Not sure just what to call that. :)
By current standards, 120/230 would indicate a three phase system while a 230/120 would be a single phase system, and in both cases they would not be possible without buck/boost somewhere, yes?

Because of those complications in identifying the terminals and wires, I would hesitate to call such a system the same nominal voltage as anything else, and would be inclined to use different wire colors attached to the wye terminals and to the delta terminals just to avoid accidents. I would do this even if that turned out not to be NEC required. (Assuming that both the wye and delta terminals were used, of course.)
As an example for thought, would you be comfortable using black wires for both sides of a 240 volt circuit just because the second line terminal was derived using a 120/120 transformer and was the same nominal voltage as the initial 120 volt circuit?
 

jim dungar

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Location
Wisconsin
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Retired Electrical Engineer - Power Systems
By current standards, 120/230 would indicate a three phase system while a 230/120 would be a single phase system, ...

By IEEE/ANSI standards and thus the NEC, via an information note, the convention for three phase systems is HV/LV and for single phase it is LV/HV. It seems the vast majority of people in the US do not follow this convention (e.g. witness the use of 120/208 and 480Y/277).
 
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GoldDigger

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By IEEE/ANSI standards and thus the NEC, via an information note, the convention for three phase systems is HV/LV and for single phase it is LV/HV. It seems the vast majority of people in the US do not follow this convention (e.g. witness the use of 120/208 and 480Y/277).

Thanks Jim! Any suggestions on how to keep it clear within this forum? Always using Y as an indicator of three phase is not intuitive when referring to a delta wired system, etc. But if you list two voltages in the first place you are pretty much tacitly assuming that there will be both wye and delta loads. I would like to see some way out of this confusion.
And, as you said in your previous post, either a 120/230 or a 230/120 description does not make logical sense for either single or three phase. :)
 

jim dungar

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Location
Wisconsin
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Retired Electrical Engineer - Power Systems
Thanks Jim! Any suggestions on how to keep it clear within this forum? Always using Y as an indicator of three phase is not intuitive when referring to a delta wired system, etc. But if you list two voltages in the first place you are pretty much tacitly assuming that there will be both wye and delta loads. I would like to see some way out of this confusion.
And, as you said in your previous post, either a 120/230 or a 230/120 description does not make logical sense for either single or three phase. :)

The Y only gets added if the system is actually a wye, nothing is added if the system is a delta => 208Y/120, 480Y/277, and 240/120 (high leg delta).

I try to use the ANSI convention and also include the number of Phases and Wires when it is absolutely necessary to avoid confusion.
240V 1PH 3W
120/208 1PH 3W
120/240 1PH 3W

208Y/120 3PH 4W
230Y/132 3PH 4W
240/120 3PH 4W
480Y/277 3PH 4W

240V 3PH 3W
480V 3PH 3W.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
I've never really thought about it, I usually place the transformers near the utilization equipment, so the likelyhood of the output mistakenly used for something else is remote.
 

don_resqcapt19

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Location
Illinois
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retired electrician
...210.5 says we need to identify systems supplied from more than one nominal voltage. Isn't 208 & 230 still the same nominal voltage?
The rule doesn't talk about "nominal voltage". It talks about voltage systems. They are different systems and require a method of identification that will permit you to identify the conductors as to both system and phase.
 

jim dungar

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Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
?????
Autotransformer driven?

120/208 1PH 3W is found in large commercial installations and apartment complexes, it is sometimes called a '120/208v network'. It can come from an 'open wye' transformer connection.
 

ronaldrc

Senior Member
Location
Tennessee
Just my two cents worth again, and some food for thought for thoughs in this
trade that want learn, and not just solely for a pay check.


No offense meant I know most common people can learn to be an excellent Electrician if
they set there mind to it, but a lot of them are just in it for the pay only. Believe it or
not when I first went to work as an Electricians helper, helpers made higher wages than
most any of factory jobs. :)

When I see 240/120 I always assumed that the 240 the left number should be the primary
and the 120 the number on the right should be the secondary. This is because usually
a Transformer diagram shows the primary on the left and secondary on the right.
If we had this rule or any similar rule set in stone we could always assume the right is the
input voltage and the left is the output voltage in this case.

What are your thoughts on this setup for a 120 to 208 volt buc Boost transformer?

I have never did this, but to me it looks like it should work, most things I post are things I have built and tried and all those work.

Would it work and are the voltages correct?



120_to_208_one_winding.jpg


Ronald :)
 

kwired

Electron manager
Location
NE Nebraska
Has anyone failed an inspection by using black, red, blue, on both a 120/208 3 phase system, and also on a 120/230 volt 3 phase system with a buck/boost transformer? 210.5 says we need to identify systems supplied from more than one nominal voltage. Isn't 208 & 230 still the same nominal voltage?

You have 2 different systems, like don said a couple posts back, you need to be able to tell which system your conductors belong to.

I think you could have 2 (or more) different 120/208 systems on same premises and you still need to have a different way of identifying each individual system.
 

GoldDigger

Moderator
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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
120/208 1PH 3W is found in large commercial installations and apartment complexes, it is sometimes called a '120/208v network'. It can come from an 'open wye' transformer connection.
Thanks Jim,

I think that I understand what your are referring to. With suitable wiring of an open wye on the output side, you can get one single phase 120 volt and one single phase 208 volt line conductor with a common neutral. But the two voltages will not be in phase with each other. That is where I had a problem with calling the whole thing a single phase service.
 
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