220 Single to 440 3ph

I've tried searching and haven't found the right thread yet and I'm sure this is a simple question that I'm probably just missing some important element of information on. So here goes...

I've got incoming 220 single phase going into my RPC with 220 3ph output. Everything is fine and works well but I need to step up at least part of the output to 440 3ph.

My RPC is wired with incoming 2 hots and a ground, no neutral. Coming out of the RPC are 3 hots and a ground. Now, when I'm looking at a step-up transformer, there's this pesky problem of needing a neutral for the second leg of each phase. From everything I've read, I understand NOT to steal the neutral from my single phase and try to use that because of funkiness that may ensue.

So, my question is, where do I get the neutral needed to step up the 220 3ph to the 440 3ph and then I what do I do with the neutral coming off of the secondary side of the transformer because I'm guessing it needs to remain separate from the other two neutrals in the system.

If someone can point me to a thread, that would be great because I don't someone to have to explain this again. I just can't find the earlier explanation.

Thanks,
-RFL

You do NOT need the neutral for the 240 side of the 240-480V transformer. If someone told you that, they are wrong.

On the HV side of that transformer, the 480V output must follow the rules of the NEC, which requires that it be EITHER grounded on one phase (corner grounded), grounded as a Wye secondary (480Y277V) or you must install Ground Fault Monitoring, which is the most expensive option. Most of the commonly available 3 phase transformers you will find will have a DEelta 480V secondary, so the "corner grounding" option is the cheapest option. If you are planning on using a VFD on the 480V side however, a Delta system is generally a bad idea, grounded or not. If that's the case, you really should look for a transformer that is 240 to 480/277 and ground the Wye point of the 480V side, even if you don't actually use it.

Thanks for the info. I had been trying to read up on my own and based on the diagrams I was finding, I thought I was seeing that the primary side needed to be grounded. I guess I'll need to look for a transformer and go from there as trying to figure it out without having an actual transformer, with diagram, is like starting from zero and teaching myself all the ins and outs of 3ph power.

-RFL

I have just purchased a 480 to 220/230 20kva 3 ph transformer (Nunome TH020U16KA +SPB) with two secondary circuits with breakers. My plan is to run this in reverse, assuming I can run the LV side in parallel to turn it into a step-up. Since the transformer is currently wired 480 Delta to 230 Wye, I'm hoping I can change that around to 230 Delta to 480 Wye.

Spec plate photo: https://portal-images.azureedge.net...ages/d2dc7f0e-be74-4b48-9225-a98901855c78.jpg

Is this a valid idea? With the multiple secondary taps, I'm hoping they can be used to get near the 440 volts I need. Unfortunately, I don't have the unit yet, so I don't have the wiring diagram to view yet.

Thanks!

Why do you need a transformer ?my rpc has 240 in 415 out with no transformer .surely you can find an idler to suit

RydForLyf said:

I have just purchased a 480 to 220/230 20kva 3 ph transformer (Nunome TH020U16KA +SPB) with two secondary circuits with breakers. My plan is to run this in reverse, assuming I can run the LV side in parallel to turn it into a step-up. Since the transformer is currently wired 480 Delta to 230 Wye, I'm hoping I can change that around to 230 Delta to 480 Wye.

Spec plate photo: https://portal-images.azureedge.net...ages/d2dc7f0e-be74-4b48-9225-a98901855c78.jpg

Is this a valid idea? With the multiple secondary taps, I'm hoping they can be used to get near the 440 volts I need. Unfortunately, I don't have the unit yet, so I don't have the wiring diagram to view yet.

Thanks!

Click to expand...

I am no expert on these, but the transformer appears to be a 480V Y to 230V Delta transformer. Seems like using it in reverse would give you what you need, 230V Delta to 480V Y...

RydForLyf said:

I have just purchased a 480 to 220/230 20kva 3 ph transformer (Nunome TH020U16KA +SPB) with two secondary circuits with breakers. My plan is to run this in reverse, assuming I can run the LV side in parallel to turn it into a step-up. Since the transformer is currently wired 480 Delta to 230 Wye, I'm hoping I can change that around to 230 Delta to 480 Wye.

Spec plate photo: https://portal-images.azureedge.net...ages/d2dc7f0e-be74-4b48-9225-a98901855c78.jpg

Is this a valid idea? With the multiple secondary taps, I'm hoping they can be used to get near the 440 volts I need. Unfortunately, I don't have the unit yet, so I don't have the wiring diagram to view yet.

Thanks!

Click to expand...

No need to be an expert. It is old news and published.

The brand you selected may not be as easy to just go find published as online information, but that information IS readily available, more common brands, and right in the product listings, not just deeper in the technical data.

Almost all, but not quite 100% - of "dry type " transformers in general are "reversible", yes.

There are minor changes, one "direction" or the other due to which set of windings was placed closest to the core and such for optimization of efficient transfer. "Minor".

Ordinarily one does not even need adjustable taps at all - or just one option typically at a nominal "5%".

Cheap test, and reduced risk?

When you THINK you have it all strapped the way you want it?

Put the 2XX side onto a common 120 V power-bar with a low amperage breaker. Typically those are but 10 or 15A. Find 2XX where you will later expect 4XX, and you have it pointed in the right direction.

Get it wrong? Small breaker trips out. Not much drama. De-power, go try harder to put the terminations where they need to be. Test it again 'til good, go "wire and forget".