What's new
What's new

Transformer vs RPC or something else?

I emailed automation direct the day you gave me this link. Today they answered and said:
"In a case where the transformer would not be used for its intended purpose, the best approach is to contact a licensed electrician to inspect and certify that the application will be adequate. "

So what in the world is a transformer's intended purpose, if not to transform power from one type of voltage to another?
They just dont have the time to babysit people through these problems.

You will want to put the 240/480v side of the transformer on the utility so your 120/240v coil can be grounded to give you center tap grounded 120v/240v american style split phase.

For a couple bullshit reasons its no longer code to allow transformers to run backwards in some areas. Hence also, the reply from automation direct.
 
Can you clarify the above transformer connections, my understanding is Canada uses split phase 240VAC single phase so you would connect the input side 240/480 as 240, and the output as 240VAC and it floats as N and L1 but the isolation transformer output is not connected to panel neutral. Transformers unless specified to be used in reverse direction my understanding is that it is no longer acceptable by NEC, there is some compensation in the windings for losses in the intended direction of use.
1712376723177.jpeg
 
Can you clarify the above transformer connections, my understanding is Canada uses split phase 240VAC single phase so you would connect the input side 240/480 as 240, and the output as 240VAC and it floats as N and L1 but the isolation transformer output is not connected to panel neutral. Transformers unless specified to be used in reverse direction my understanding is that it is no longer acceptable by NEC, there is some compensation in the windings for losses in the intended direction of use.
View attachment 435392
Yes, my objective all along is to convert my household 240V split phase (live live ground) to 240V single phase (live neutral ground), and I am having a difficult time figuring out how to do it safely and properly so it can pass inspection.

I have been reading the transformer manual, it says E/2E such as 120/240:
E/2E shall indicate a
winding; the sections of
which can be connected in
parallel for operation at E
volts, or which can be
connected in series for
operation at 2E volts, or
connected in series with a
center terminal for three-wire
operation at 2E volts between
the extreme terminals and E
volts between the center
terminal and each of the
extreme terminals.


From this I think I need this on the input side as I think 3 wire operation input is what I need.


and V x V such as 240 x 480 means:
V 􀁵 V1 shall indicate a winding for
parallel or series operation only but not
suitable for three-wire service.

I think this is the type that is needed on the output side.

However, I might still be misunderstanding, as the quote Larson sent me was VxV primary and E/2E on the secondary.
 
Both input and output would be two wire, so there is no need to swap primary/secondary. You don't want to connect the neutral on the primary side.

You would still earth the secondary side neutral. We don't really want a floating supply, which would have an L1 and L2 without a neutral (some VFDs have warnings against use on floating supplies). We want an EU-style grounded neutral, and a phase conductor at 220/230/240V to that neutral.

It's perfectly suitable for the application.

However, I still see serious questions with the need for such a transformer.
  • Operating on split-phase is less stressful for the VFD than on a single-ended supply. Higher voltage to ground.
  • They've installed a two-pole breaker, so this is clearly not some stupid situation where the neutral is earthed inside the VFD.
  • The VFD still needs to be rated and tested for a significant voltage between neutral and earth - in most (all?) cases, the P-E test requirements are identical to N-E requirements.
  • Most VFDs are fully labelled for L/L1 and N/L2.
I suspect the manufacturer is merely arse-covering rather than providing competent engineering.

Further, if you are expecting this to be competently inspected...
  • None of the componentry will be UL listed. Breakers, transformer, enclosure, control board, maybe VFD, motor, cabling etc.
  • You'll need to use 277V rated gear for everything on the secondary of the transformer, as it's more than 150V to ground.
  • The gear is no more compliant for US operation at straight 240V than at 120/240V. I know gear has been rejected in NZ because it was labelled as '200V' or '220V' when the legal requirement is 230V.
I wouldn't be surprised if it was cheaper and maybe easier to scrap the Chinese controls entirely and install a new VFD and throw together new controls.

If you can, contact whatever inspector would be inspecting it and find out what they want before spending money that might not fix the problems.
 
Both input and output would be two wire, so there is no need to swap primary/secondary. You don't want to connect the neutral on the primary side.

You would still earth the secondary side neutral. We don't really want a floating supply, which would have an L1 and L2 without a neutral (some VFDs have warnings against use on floating supplies). We want an EU-style grounded neutral, and a phase conductor at 220/230/240V to that neutral.

It's perfectly suitable for the application.

However, I still see serious questions with the need for such a transformer.
  • Operating on split-phase is less stressful for the VFD than on a single-ended supply. Higher voltage to ground.
  • They've installed a two-pole breaker, so this is clearly not some stupid situation where the neutral is earthed inside the VFD.
  • The VFD still needs to be rated and tested for a significant voltage between neutral and earth - in most (all?) cases, the P-E test requirements are identical to N-E requirements.
  • Most VFDs are fully labelled for L/L1 and N/L2.
I suspect the manufacturer is merely arse-covering rather than providing competent engineering.

Further, if you are expecting this to be competently inspected...
  • None of the componentry will be UL listed. Breakers, transformer, enclosure, control board, maybe VFD, motor, cabling etc.
  • You'll need to use 277V rated gear for everything on the secondary of the transformer, as it's more than 150V to ground.
  • The gear is no more compliant for US operation at straight 240V than at 120/240V. I know gear has been rejected in NZ because it was labelled as '200V' or '220V' when the legal requirement is 230V.
I wouldn't be surprised if it was cheaper and maybe easier to scrap the Chinese controls entirely and install a new VFD and throw together new controls.

If you can, contact whatever inspector would be inspecting it and find out what they want before spending money that might not fix the problems.
If both input and output are two wire, then it shouldn't matter if I use 240x480 or 240/480, and I can look for whichever is cheapest.

I would guess the manufacturer has to be at least partially arse-covering, because if something goes wrong on the other side of the world, supplying support is difficult. If their choice is to have the customer spend extra on a transformer so they are confidant the product works as tested; else the customer experiments with a untested power type that could go sideways... Well, I would always expect them to take the safer route.

The manufacturer did tell me in writing that all electrical components in the compressor are UL certified. If I can get a transformer that is UL certified, then that should be good enough.

This is the first compressor I have used that is oil-free scroll type, so I am much less confidant about replacing control systems than I would be for a piston style. I would like to have it operating properly for several months to get accustomed to how it operates and what it needs for regular maintenance before I would want to implement changes.

Thank you for the comments though, anything that assists my learning process is appreciated.
 








 
Back
Top