Operating 480VAC 3 phase motor with 240VAC single phase power

I just purchased a Gorton Mill. Control box was labeled 480VAC. When attempting to change the voltage the machine came with a wiring diagram but when attempting to reconnect the main motor I found that it was probably rewound 480VAC. Name tag was removed as well a the connection plate. Only 3 wires were available and none are marked. So I have to run it on 480VAC. I've done it before when I purchased a B&S mill, it too was wired 480VAC and came with a transformer. Sold the mill but still have the transformer plus I have a few single phase transformers large enough to handle the motor on the Gorton mill. Which way will be better, have the RPC wired to the low voltage connected to a 3 phase transformer or single phase transformer connected to the low voltage and connect a RPC wired for 480VAC wired to the output of the transformer?

Froneck said:

I just purchased a Gorton Mill. Control box was labeled 480VAC. When attempting to change the voltage the machine came with a wiring diagram but when attempting to reconnect the main motor I found that it was probably rewound 480VAC. Name tag was removed as well a the connection plate. Only 3 wires were available and none are marked. So I have to run it on 480VAC. I've done it before when I purchased a B&S mill, it too was wired 480VAC and came with a transformer. Sold the mill but still have the transformer plus I have a few single phase transformers large enough to handle the motor on the Gorton mill. Which way will be better, have the RPC wired to the low voltage connected to a 3 phase transformer or single phase transformer connected to the low voltage and connect a RPC wired for 480VAC wired to the output of the transformer?

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Pluses and minuses to each. I tend to prefer a common-iron, AND NOT built-from-singles, 3-P transformer between RPC and load. Goes a way - a SMALL way, but still - toward sharing generated leg imperfection. Overall power is the same, tuning for balance is a bit better.

Motors like balance easily as much as perfection.

Good place to use a Delta-Wye and re-derive a new on-box locally referenced neutral, too, where controls or lighting might need stable and somewhat less "which leg" dependent single-phase AC

2CW

I built a 10 hp RPC that did just that, for a jig bore 480 vac only.

Standard 10 hp motor at 240 vac, 3 phase xformer to step it up.

digger doug said:

I built a 10 hp RPC that did just that, for a jig bore 480 vac only.

Standard 10 hp motor at 240 vac, 3 phase xformer to step it up.

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BTW - there's the OTHER benefit to an idler at line voltage, transformer AFTER.

My 240 <==> 480 15 KVA transformer has been disconnected, merely keeping the back patio slab from blowing away in a high wind since deciding I was NOT going to use any 460/480 VAC at all - even if I had to change a motor (not needed, one to go, all others were dual-voltage).

The 10 HP RPC and idler? Already 240 VAC. No change needed at all.

If I had put the step-up ahead of a 480 VAC idler? Then.. I would have need to re-strap it for 240. Or maybe even step back DOWN if that idler had been chosen for getting some use out of a single-voltage wound motor.

2CW

My RPC is actually more than one motor. The main motor is 3HP delta wound. If I need more HP another motor can be switched in, 5HP but 6 poles. Haven't needed them yet but I do have a few 6 pole motors up to 15HP. What's nice is that 3HP delta wound will start and keep running even under heavy cuts a 5HP 6 pole motor on my 14" Hendey. It will start as if connected to 3 phase. Also my 24" Hendey with 7.5HP 6 pole will start but needs to windup and will struggle when heavy cut are taken at the higher speed range, the 5HP RPC motor is usually switched in easily started by the 3HP RPC motor. It did come with the 15HP I mentioned above. I also have a 5HP 8 pole motor I found at HGR. The transformer I mentioned is quite odd. Has what I think is the secondary with 3 voltage (190, 200 and 210) connections, probably Y since is has a neutral. The primary is odd too. Each of the three coils has 10 voltage connections. 2 identical groups of 5 numbered from 1 thru 10 (1) 0, (2) 200 (3) 220 (4) 230 (5) 240 Then repeats the sequence (6) 0 ------(10) 240. As wired when I received it #10 (240) was jumped to #1 (0) and output connected to (5) 240 which was 480VAC. Using it what I assume connected backwards I connected the lower voltage of the generated phase from the RPC to the lower voltage terminal. Haven't used it since I sold the B&S mill. Some day when I have time I might connect an O'scope to that 8 pole motor to see what I get when using it as an RPC. I have the shop wired so that the generated phase is always on the same wire color and terminal of a twist lock receptacle and plug. When connected to the machine the non generated phase is always connected to the single phase input of the controls. On this machine the single phase use will be greater than usual since it has a transformer large enough to supply 2 small DC motors that are used as the variable speed feed motors. I will double check to make sure I'm correct.

Froneck said:

My RPC is actually more than one motor. The main motor is 3HP delta wound. If I need more HP another motor can be switched in, 5HP but 6 poles. Haven't needed them yet but I do have a few 6 pole motors up to 15HP. What's nice is that 3HP delta wound will start and keep running even under heavy cuts a 5HP 6 pole motor on my 14" Hendey. It will start as if connected to 3 phase. Also my 24" Hendey with 7.5HP 6 pole will start but needs to windup and will struggle when heavy cut are taken at the higher speed range, the 5HP RPC motor is usually switched in easily started by the 3HP RPC motor.

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Happy for yah, you have a winner. But that don't sound like no ordinary THREE HP motor of "the usual" slip category. Memory fades, but the way it behaves I'd guess the lower curve right down close to torque motor turf.

Might calculate FLA @ nominal Voltage against KW and nameplate HP, find it has rather lower than usual conversion efficiency, too.

have a 5HP 8 pole motor

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Not a lover of 2-pole, personal hearing "recruitment" issue, acoustically.

But don't waste too much time on 6 or 8 pole for idlers. Too much "sharing", parasitizes efficiency. They make far the better load motors than idlers.

The transformer I mentioned is quite odd. Has what I think is the secondary with 3 voltage (190, 200 and 210) connections, probably Y since is has a neutral.

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That part is standard, if not vanilla, nominal 10% taps, 5% are more common, neither are odd, just a premium-priced option.

The primary is odd too. Each of the three coils has 10 voltage connections. 2 identical groups of 5 numbered from 1 thru 10 (1) 0, (2) 200 (3) 220 (4) 230 (5) 240 Then repeats the sequence (6) 0 ------(10) 240. As wired when I received it #10 (240) was jumped to #1 (0) and output connected to (5) 240 which was 480VAC. Using it what I assume connected backwards I connected the lower voltage of the generated phase from the RPC to the lower voltage terminal.

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Also not as UNcommon as first appears. Multinational market. Even US/Canada or either/Japan are not identical schemes. Europe is the other. It wont have all THAT many choices, but again has incremental taps to adapt to site or plant specific deviations due to length of run - wotever.

Probably left home inside a not-so-cheap CNC critter. Milacron reports-out similar complexities now and then on high-grade machine tools. Others are all over ebay as part-outs, Fanuc pulls one of the more common.

Haven't used it since I sold the B&S mill.

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Sort o kit I used to chase when I was still test-benching. Prolly too low a KVA (6.6 KVA - maybe less?) for what I seek NOW - a couple of Delta-Wye for the 10 HP Phase-Perfects.

Always DETESTED corner-grounded / high-leg / stinger Delta. DoD was a largelya 208/416 Wye world, and I'm still good with that.

The transformer is at least 15K. Don't look like the enclosure it's in is original. Much larger than necessary and has a 30A breaker mounted in a square hole cut in the box and connected to the 480 side of the transformer. Rather than corner ground I'm thinking of grounding the center of one the coils connected in series but not all of them. I've done that on one of those delta connected transformers that has has one coil center tapped for low voltage single phase.
I too am not fond of 2 pole motors, I haven't tried 6 or 8 pole motors as RPCs but I've always wondered how they would preform but haven't found the time! I have that 5 HP connected so I can switch it in if needed but usually start the 5 HP on the 14" Hendey when I want to take heavy cuts with the 24" simply because it's a shorter walk! Being lazy I like to take as big of a cut as possible, more material I remove is less time at the machine! I haven't had HP problems yet but then I'm not using the higher speed range very much since I use the smaller lathes for smaller diameter work.
I did check the wiring diagram/schematic and the only motors using input power is the spindle, coolant pump and power knee motor. The other 2 feed motors use power connected to a single phase transformer which also powers all the contactors. I will check and determine if the transformer I have is a Y-Y or Delta-Y. I'm always checking HGR to see what transformers they have. I did get one that has a multi tapped Delta primary in 220 volt range and 208 Y out. Also found some low voltage 10 and 11vac but large KVA and someday intend to make a 12v battery charger/jumper (so I don't have to wait for the battery to charge)

Froneck said:

Rather than corner ground I'm thinking of grounding the center of one the coils connected in series but not all of them. I've done that on one of those delta connected transformers that has has one coil center tapped for low voltage single phase.

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? Using the "lighting" tap as ground is just not on my dance-card. I don't like corner-grounding, but it would be the better choice.

why not use the lighting leg? Wouldn't that be almost the same as the open delta 3 phase connected by the power company in many places. 2 legs are 120VAC to neutral/ground and the other is about 200VAC commonly referred to as the "Wild Leg"
Connected my transformer today, My Gorton mill runs great! Spindle runs very quiet. Should the variable speed belt is in a completely closed cast iron housing. DC down feed motor works good too but table feed don't. Might be I'm not operating it properly since it also has a rapid travel feature. Knee power works too but I'm going to do some changes, same with the spindle reverse switch, it kinda in a stupid place! One good thing the Maintenance manual has a schematic of the power feed controls.

Froneck said:

why not use the lighting leg? Wouldn't that be almost

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"Almost" if pitching horseshoes is the game, or all you do is put a meter on it or light loads.

See NFPA 70, available as a .pdf download for under $35, not terribly costly as dead-tree.

Or query the maker of your transformer or any comparable new transformer for their specific limitations. Rating of that tap may be around 15%, typical max, sometimes as little as 5%. Check it out. That is not a secret. Published information.

Take further note of what those limitations impose on protective devices and switchgear in order to remain compliant with the National Electrical Code. AND NOT what the careless, klewless, or arrogant who consider themselves VASTLY ABOVE any such rules may "opine" as "good enough" for their HALF-VAST world.

Basically, it taps but ONE of three coil-sets, has a limited current carrying capability, involves inductance, is not in overall balance all the time, and is not "really" a point of equilibrium amongst all THREE phases across the full range of possible loading.

The nexus of a Wye transformer IS all of those things, and that has serious value.

Light load OR borderline disaster, a "WYE" transformers central winding nexus can be trusted to be what it is - a Neutral point, regardless.

Use the right transformer for the task, other things are simpler, cheaper, more easily kept code-compliant, and you have time to go do something more useful instead of screwing around at re-inventing hundred-plus year old wheels that their industry has already spent a b**y fortune on researching and learning from so as to write those rules.

thermite said:

"Almost" if pitching horseshoes is the game, or all you do is put a meter on it or light loads.

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enough of the bullshit.

Froneck said:

why not use the lighting leg? Wouldn't that be almost the same as the open delta 3 phase connected by the power company in many places. 2 legs are 120VAC to neutral/ground and the other is about 200VAC commonly referred to as the "Wild Leg"

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yes

Froneck said:

why not use the lighting leg? Wouldn't that be almost the same as the open delta 3 phase connected by the power company in many places. 2 legs are 120VAC to neutral/ground and the other is about 200VAC commonly referred to as the "Wild Leg"
.......

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A "lighting tap" transformer is usually made with a bit larger wire on the center tapped winding, because they know that will have extra load on it. Makes for imbalance on the 3 phase supply, but works.

No clue what would be wrong with it as a connection, causes less trouble of adapting than corner grounding, but for one machine that is not an issue in most cases.

Not clear on how you want to wire it. If the HV side is wye, you don't need to do anything odd. If the HV side is delta, as it seems, yes ground the center tap and you have a 480V version of "lighting tap" output.

Problem I see is that the switchgear has to be good for more than the usual 277 V to ground. But not as much as corner ground would put on it.

If you make the transformer "part of the machine", so you are not creating a "branch circuit", I do not think you really need to ground it either way, although I would.

JST said:

Problem I see is that the switchgear has to be good for more than the usual 277 V to ground. But not as much as corner ground would put on it.

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Maybe not, but the code treats it as if. 480 AND NOT 480/277, f'rinstance.

In-machine or in machine-specific enclosure, not a big deal.

de facto if not also de jure branch, serving many machines, wise to adhere to code.

And code, of course, needs no "clever cheating".

Most any work-around common is right there IN today's code where covered as legacy, or common and familiar "when-one-must" alternatives.

Code dasn't say "may never" as often as it says "do these extra things to stay safe when you have no other choice".

Code can be every bit as much "pre approved cheat sheet" as strict Mosaic law. It wasn't laid-down by a lone GS5 Law Clerk with a rod up the arse.

NEC is the product of the field experience of tens of thousands of practical folks over long, long years. Alternatives, their limitations, and how they are meant to be dealt with are right there IN it.

Yes light loads but if not using it as a current carrying neutral but rather having the Delta output ground referenced so as to prevent shock hazard and if available use it instead of corner grounding. Most of the transformers available are Delta primary Wye. At one time I did know why Delta was a better type of Primary but forgot and for most shops that are using transformers backwards simply because there are a lot of Delta primary transformers available cheap. HGR has quite a few of them at a small fraction of new cost only issue is distance but I'm sure there are other used equipment suppliers/junk yards so that cheap transformers are available. I have no affiliation with HGR, I buy from them because they have low cost items however buyer beware that a lot of the stuff is there because it has a problem so it's better to inspect it before purchase.
I agree that if a step-up transformer was needed a low voltage Delta primary with a Wye high voltage secondary can be purchased new is the best way but I like many others here are doing things on a shoe string and create 3 phase with a home made RPC gadget. I'm retired and run my shop to make some extra cash, if 3 phase were available on the pole I wouldn't have it connected. With 3 phase comes a demand meter that will double the cost or more for the small power user.
As to my transformer, as connected when I got it is Wye on the what I assume was the intended primary and I'm using it backwards. The other side is Wye too with a neutral. The secondary (side I'm using as my primary) is internally connected WYE but the Primary has 10 connections an no internal connections however there is no chart or any other information so as to be able to connect it Delta.

thermite said:

Maybe not, but the code treats it as if. 480 AND NOT 480/277,.....

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Matters in the switchgear. etc.

Example: A household breaker box carries "240V", but only when supplied as 120/0/120V, which has only 120V to ground. It is NOT RATED for 240V to ground in most cases.

It is stuff like that that makes the difference. The wires etc generally need to be rated for the highest "voltage difference" in the box or raceway.

I would think that the voltage rating wire to ground is all that is necessary. Plus the rating has to take into consideration the peak voltage not the RMS equivalent. I understand that the voltage difference between the wires be twice the voltage to ground in single phase yet wire to wire will have double the insulation. Insulation requirement for 480VACRMS is 600V yet the peak voltage be at the point break over will happen is near 680Vacp-p, same will be for single phase 240vac, 300V wire is used yet the peak wire to wire voltage is 340vacp-p. The lower voltage rating of the wire insulation than the peak to peak voltage is because as I mentioned above the insulation between the wires is double.
Back to my Gorton, I did find the reason my table power feed was not working, it's interlocked with the spindle down feed. Both motors use the same feed control, a switch on the down feed pot must be in the off position, reading the manual helped! But I couldn't get it to the turn off. In addition I had little variation in down feed available, fast or nothing. Removing the cover I seen a pot with a switch. I cut the wires since the pot was clearly marked as to where the wires were connected, also made a wiring diagram. Ohm meter on the pot indicated it was open, bending the tabs on the case I opened it and seen where the switch was tripped and tripped it after taking continuity checks before and after, switch will open in the "off" position, being I cut the wires and they were clear of anything else I power-up the mill, table feeds great! The pot marked only with part numbers I tried to determine the value but couldn't however looking at the wiring diagram/schematic it's listed at 10K. The one installed also had a second pair of contacts that would close in the off position thought unused. I will now try to find another pot with the same dual switch and connect an indicator light to the other set of contacts.

The assumption is that there may be a bare connection, or other such in a box, which the wire might lay against, so the insulation is rated for full wire-to-wire voltage. That issue is more common with small wires than large cables, of course, because in wiring boxes for small wires the wires may lay anywhere, and large cables are usually more controlled. But the same requirement is carried through.

The voltage rating is rms.... 600V wire is good for 480VAC , even though peak is nearly 700V, because the wire insulation is good to 600VAC. Don't make more complicated than it really is.

UL, which rates the wires, does not even deal with anything over 600VAC. That and above is termed "medium voltage", and is generally industrial and utility related..

Froneck said:

I would think that the voltage rating wire to ground is all that is necessary.

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The point is.. not that one should shut-down the brain - but that we are almost NEVER the first with a need to know or do, certainly not with regard to the safe implementation of electrical power distribution and use.

When Dad left US Coast & Geodetic Survey, 1931, to take-on a new job as a construction inspector, NACA Langley, the "Full Scale Tunnel", then later its local power plant? The Electrical Code may not yet have grown to even 200 pages. When I moved-off a 1949 thin pamphlet of H.P. Richter's "House Wiring Simplified" to step-up to a "paper" copy of "the Code" ISTR it was certainly still under 400 pages. U.S. Army Corps of Engineers course in "Utilities in the Theater of Operations" mid 1960's distilled only the most essential bits we needed to around a hundred pages or less. Even so, water and sewer were covered, not just power.

Present-day NFPA 70 is listed at just short of NINE HUNDRED pages. MUCH of that growth is due to the inclusion OF the workarounds wanted to deal with legacy work no longer considered safe without a bit of extra care.

The "extra care" wanted for your case could easily cost more to implement that simply going and finding a proper "Wye"-secondary transformer that was MEANT to re-derive a local neutral the day it was wound.

That simple. Dollars and cents exercise, not a technology exercise.

"The internet" will FIND what we need OUT OF all those pages, and in mere minutes.

Including coalescing the four or five different sections that apply to the very issue you are wandering about over.

Go and look it up. I did that days ago.

You can DO that. I am certain you will "get it in one", because "the code" does not just "dictate". It educates, too. It explains WHY things need to be done a certain way.

It does no good for ME to do that.

You will only "OWN" that sort of information for your very own use, going forward, if you do that sort of "homework" with your OWN brain, not a with collective alloy of brains borrowed off PM.

looking at the wiring diagram/schematic it's listed at 10K. The one installed also had a second pair of contacts that would close in the off position thought unused. I will now try to find another pot with the same dual switch and connect an indicator light to the other set of contacts.

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Pots of that sort are "built up". One can stack them by hand from loose components if need be. Just pick a "family" meant to be stacked as multiple pots and/or a switch or three. A B is good. "J" series if old memory serves.

Old skewl table radio, stereo, TV, automobile and portable audio were the high-unit-count examples. Potentiometer to serve as "Volume" control had a switch stacked onto the back of it to turn off the power.

Nearly as common as housefly poop, IOW.

Just do it.

At least I have a Wye transformer so I'm to code. I like to keep all my power ground referenced. Putting 10 pound of machinery in a 5 pound building has my machine quite close together I do want to someday put my hand on one and touch another and get zapped. I'm very interested in safety as it will be me that get hurt!
Yes I know pots are stack able, done it may times but some pots are not. The one in my machine is not stacked the switch is part of the main housing. I'm in the middle of no where. Since Radio Shack is gone we have no electronic supply house. Even when Radio Shack was here the slowly went out of the component business but at least it could be ordered.
One in my machine is about 1" in diameter possibly 1/4 watt maybe 1/2. I'm thinking a larger diameter pot will give me finer control at least it won't hurt to put it in, lots of room!

Froneck said:

At least I have a Wye transformer so I'm to code. I like to keep all my power ground referenced. Putting 10 pound of machinery in a 5 pound building has my machine quite close together I do want to someday put my hand on one and touch another and get zapped. I'm very interested in safety as it will be me that get hurt!
Yes I know pots are stack able, done it may times but some pots are not. The one in my machine is not stacked the switch is part of the main housing. I'm in the middle of no where. Since Radio Shack is gone we have no electronic supply house. Even when Radio Shack was here the slowly went out of the component business but at least it could be ordered.
One in my machine is about 1" in diameter possibly 1/4 watt maybe 1/2. I'm thinking a larger diameter pot will give me finer control at least it won't hurt to put it in, lots of room!

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For no reason I can actually recall, I looked up their company background and discovered I had become a Digi-Key customer in their earliest years and still am. Allied Radio and Lafayette long before that. Also Mouser a tad more recently and Newark from the late 1960's onward. Power-One, first year, too. Arlington Electronics, Capitol Radio, and for a time Potomac Aviation and Marine were the only "local" places worth a damn, Metro DC.

Radio Shack was never worth spit, their best days, unless you expected to build to whatever hobby-schlock they HAD instead of what you NEEDED - MIL-SPEC or industrial-grade as often as not for my needs.

"Fun" was having to alter 2 dozen telco rackup line units from single-output channel to dual in a posh suite of the Okea Plaza hotel, Tokyo for gear installed practically next door, KDDI, internationals gateway switch center.

The goods had been designed for dual-channel, had been so promised on contract for least-cost routing, , but had arrived populated for single-channel only. All they needed was de-soldering a PCB DPST relay, replacing with DPDT, which should have never been otherwise - downloadable firmware and configurable software doing the real work, anyway.

Comical part was the Danish designer back in Silkeborg fussing over not being able to get the parts to me fast enough.

"Uhh Per? It's a stock JAPANESE relay. I'm IN Tokyo. I'll find them in Akihabera in about 20 minutes of slithering through narrow aisles 'tween tiny tables."

And did so. Also solder-sucker, wicking braid, good solder, and a VERY decent dual-temp iron.

Taipei has a similar "zone". Hong Kong as well.

Brunei? Not so much - you just have to fly in and out more often. Enough so the Security Chief invites you up to the top deck to watch some guy do "touch and goes" in a four-engined Airbus, of all things!

"Who would do touch and goes HERE at this airport, in a "heavy?" I ask.

He grins. "Our Sultan. He is upgrading his rating from his twin Airbus to his new one."

Shopping trips to London, he'd fly one, a former RAF crew the other one. That was so that not all his wives were on the same aircraft, and the Crown Prince was not on the same aircraft as his Dad flew.

Careful guy, the Sultan of Brunei. Also wealthy. Magical array of telco gear. Enough to run a country 20 times larger, and with 100% redundancy plus-plus, even so.

His dream? Another Zurich or London as financial hub. In Asia.

Otherwise, when the oil runs out, it is back to subsistence fishing for his people.



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