Wiring Rotary Phase Converter To Transformer To Lathe

Degull · Sep 24, 2020

Hi everyone. I have a 10hp 230V rotary phase converter and 240V/600 Wye Delta isolation transformer that I would like to wire it to my lathe that requires 575V. My shop has single phase 220V. I have the rotary phase converter wired directly to my circuit breaker panel. The RPC will feed the low side of the isolation transformer and the transformer high side will feed the lathe.
Do I need to install fused disconnects between the RPC/transformer and the transformer/lathe?

rpseguin · Sep 24, 2020

I would, or even better, get a 3 phase breaker/box for between the RPC and the load (your lathe).

Degull · Sep 24, 2020

rpseguin said:
I would, or even better, get a 3 phase breaker/box for between the RPC and the load (your lathe).

So I need two disconnects? One between the RPC and the transformer and one between the transformer and lathe?

rpseguin · Sep 24, 2020

Degull said:
So I need two disconnects? One between the RPC and the transformer and one between the transformer and lathe?

Is the lathe going to be the only thing hung off your transformer?
I would probably just put a 3ph load center with breakers hung off the output of the RPC, and have an appropriately sized breaker for your transformer/lathe.
What are the ratings/draw of the lathe at 575V? Scale that amperage up for the RPC output voltage.
I’m hoping wiser people chime in.

dalmatiangirl61 · Sep 24, 2020

You should have a disconnect between breaker panel and rpc, I am not a sparky so know nothing about codes, but that is what mfr of my rpc recommends. I'm in a similar situation in getting my rpc going, what I am not understang is why they also say to use a fused disconnect, its seems to me that breaker and fuses is redundant.

rpseguin · Sep 24, 2020

dalmatiangirl61 said:
You should have a disconnect between breaker panel and rpc, I am not a sparky so know nothing about codes, but that is what mfr of my rpc recommends. I'm in a similar situation in getting my rpc going, what I am not understang is why they also say to use a fused disconnect, its seems to me that breaker and fuses is redundant.

But a breaker is a switch and disconnect.
I suppose it is because a disconnect switch is probably designed for many more manual switching cycles than a breaker. And may be more conveniently located.
But breakers are inexpensive compared to fuses and disconnects.

My setup: 25HP RPC feeding 240V 3ph machines and a 30KVA step up transformer which feeds my 440V machines.

I currently have my RPC strung straight to my breaker panel, but I plan on putting a 1ph 2 pole breaker box in between my panel and the RPC as a disconnect and more convenience for the occasional trip of the main panel breaker on RPC startup.
I want to put a 230V 3ph panel on the output side of the RPC and a 460V 3ph panel on the output side of the transformer, with individual breakers for each machine.

BTW, I use these to get an at a glance view of power consumption:

100A AC LCD Digital Volt Watt Power Voltage Meter Monitor KWh Voltmeter Ammeter 760970220593 | eBay

I have one on the line feeding my RPC and some on individual circuits.
I’m looking for a 480V capable version that is reasonably affordable.

Homebrewblob · Sep 24, 2020

In my research on my own RPC build they also recommended fuses AND breakers.

I am probably getting something backwards but as I know it under Voltage spikes and flux the fuses are SUPER reliable and FAST acting vs breakers don’t always pick up on volt flux or spikes only overdraw current.

Fuses AND breakers TOGETHER is the best choice.

I also agree, get a breaker box and fuses disconnect between your transformer and lathe,
The wiring and fuses/breakers between your RPC and supply lines are dependent on your specific wiring configuration.

rpseguin · Sep 24, 2020

Homebrewblob said:
In my research on my own RPC build they also recommended fuses AND breakers.

I am probably getting something backwards but as I know it under Voltage spikes and flux the fuses are SUPER reliable and FAST acting vs breakers don’t always pick up on volt flux or spikes only overdraw current.

Fuses AND breakers TOGETHER is the best choice.

I also agree, get a breaker box and fuses disconnect between your transformer and lathe,
The wiring and fuses/breakers between your RPC and supply lines are dependent on your specific wiring configuration.

Interesting.
What voltage spikes are they going to respond to?
Many of the fuses/fused disconnects I have looked through have 600V fuses, so it seems like the fuses are set up for overload current. And many of those are slow blow fuses too.
I would think that tripping on voltage fluctuations would be a bad thing with an RPC, at least on startup or startup loads from machines.
Can you please share some reading material?

Thanks!!

Homebrewblob · Sep 24, 2020

I don’t remember a single location that contained the info.

A quick google search found this

https://www.eaton.com/content/dam/e...-lib-circuit-breakers-reclosing-resetting.pdf

But it may not contain the info your seeking

I didn’t read though this link in entirety and like I said the reasons for both fuses and breakers in my eyes was for multiple reasons not just overdraw

Fuses can be sized very close to operating amps and still sustain motor startup influx.

While breakers HAVE to be OVERSIZED to resist motor startup influx.

So I guess I was backwards.

OVERSIZED BREAKERS are fast acting in a real Bona fide short circuit fault.

While fuses are more equip at protecting motors against sustained overdraw current

So use both.

I run both in my setup

rpseguin · Sep 24, 2020

Homebrewblob said:
I don’t remember a single location that contained the info.

A quick google search found this

https://www.eaton.com/content/dam/e...-lib-circuit-breakers-reclosing-resetting.pdf

But it may not contain the info your seeking

I didn’t read though this link in entirety and like I said the reasons for both fuses and breakers in my eyes was for multiple reasons not just overdraw

Fuses can be sized very close to operating amps and still sustain motor startup influx.

While breakers HAVE to be OVERSIZED to resist motor startup influx.

So I guess I was backwards.

OVERSIZED BREAKERS are fast acting in a real Bona fide short circuit fault.

While fuses are more equip at protecting motors against sustained overdraw current

So use both.

I run both in my setup

Thanks! Interesting short read, but I don’t think this is the right article for this.
It doesn’t mention anything about voltage spikes/variations, but does say that fuses can be selected to better protect the starter circuit. It does bring up the good point that once a fuse blows, and you replace it, you supposedly have new/original level of circuit protection. It says that with a breaker, after a fault trip, you don’t know how many cycles it will take.

Apparently, I’m supposed to have an electrician on staff and an electrical spare component store room :-)

All that said, single phase 2 pole breakers are often less expensive than fuses, so I could choose to replace a breaker every time it trips, it would still be less expensive than replacing fuses...
Time-wise resetting a breaker hands-down beats opening a fuse box, ringing out and replacing fuses.

I’m going to do some digging around to find out more about what you mentioned.

I have several fused disconnect boxes, but I haven’t deployed them yet simply because of the cost of fuses.

rpseguin · Sep 24, 2020

I use breakers sized for operating load, not inrush startup current, as I soft-start my RPC.

Homebrewblob · Sep 24, 2020

rpseguin said:
I use breakers sized for operating load, not inrush startup current, as I soft-start my RPC.

I have big start caps on my 3rd leg and blast start my RPC to life.

Waiting for my c winding to fly out the side of the rpc motor

And yes! Like I said I did ALOT of google university to come to my conclusion, I don’t remember seeing any one article that covered the fuses and breakers in a RPC setup so I kinda came to the conclusions with everything I read.

I keep 2 Electricians on staff all times, a pitbull and Akita,
The pit bull is into chewing the wiring and the Akita is more into sounding off when something’s amiss.

Can’t get them to actually fix anything but ya know the Union wont let me fire them

rpseguin · Sep 24, 2020

Homebrewblob said:
I have big start caps on my 3rd leg and blast start my RPC to life.

Waiting for my c winding to fly out the side of the rpc motor

:-)
Funny! Just don’t be in the way!
Mine annoyingly whines like a jet engine while it is coming up to speed.

I was semi-seriously/half-jokingly considering getting a 200HP motor to use as an RPC.
My friend bought it instead.

That orange power cord you can see going into the 100HP ABB VFD is a 14 gauge extension cord carrying 460V 1ph...

Running a 200HP 3 Phase Motor from Single Phase Power and a VFD - YouTube

We ran that 1700RPM 200HP motor up to 80Hz/2400RPM

Homebrewblob · Sep 24, 2020

rpseguin said:
:-)
Funny! Just don’t be in the way!
Mine annoyingly whines like a jet engine while it is coming up to speed.

That orange power cord you can see going into the 100HP ABB VFD is a 14 gauge extension cord carrying 460V 1ph...

I like you more with each comment like this!

Also that’s why I located my idle motor outside my garage behind a poured foundation! No noise and no shrapnel!!

BT Fabrication · Sep 25, 2020

Degull said:
Hi everyone. I have a 10hp 230V rotary phase converter and 240V/600 Wye Delta isolation transformer that I would like to wire it to my lathe that requires 575V. My shop has single phase 220V. I have the rotary phase converter wired directly to my circuit breaker panel. The RPC will feed the low side of the isolation transformer and the transformer high side will feed the lathe.
Do I need to install fused disconnects between the RPC/transformer and the transformer/lathe?

Yes, here in ontario you need switches between each power source for isolation.
they are only $100 for a 3 phase disconnect.

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