# Need 480 Volt 3 phase from 240 1 phase source



## HARRY304E

kbsparky said:


> I have a job to connect an irrigation system in a rural area. It requires 480 Volt 3 phase power.
> 
> The only available utility power here is 120/240 Volt single phase.
> 
> I am trying to determine whether I should recommend a rotary phase converter for this setup, or should we simply move on to the 21st century, and specify using a VFD?
> 
> The irrigation pump is 25 HP, and the rest of the system has (4)½ hp drive motors, and a 2½ booster pump. All of them operate at 480 Volts, 3 phase. Even the control box requires 480 Volts for its operation.
> 
> Would it be cost effective to get a VFD unit(s) that have a 240/1 Volt input, with a 480/3 output?
> 
> Edit to add: I understand that most rotary phase converters only add a phase, and I would also need a transformer to step up the output to 480 Volts as well.


I would say that you are better off using a VFD.

With a Rotory phase converter i believe you would also need a transformer right.


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## micromind

I don't know of any VFDs that have 240 1ø input and 480 out. It might be hard (and expensive) to find one that could handle this much load. Some 3ø drives can accept single phase input, but you have to oversize them. 

A rotary phase converter and a transformer would likely be less money and more readily available. 

Is the pump submersible? If so, it will be more sensitive to voltage imbalance, a VFD will produce better balance than a phase converter. a 2-1/2HP motor sounds IEC to me, these motors are way sensitive to voltage imbalance. 

If you could get a transformer that is 240∆ to 480∆ it'll help with the voltage balance. I'd suggest a 45KVA, a 30 will be pushing it a bit. Check into drive isolation transformers as well as basic power transformers.


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## kbsparky

Yes, the pump is submerged in the well.

The 2½ booster pump is located at the far end of the irrigation array. It boosts the flow for the outer nozzle, so it can get passing cars wet .... :laughing:


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## user4818

kbsparky said:


> The only available utility power here is 120/240 Volt single phase.


I'm curious as to why this is the case. No 3 phase primary voltage available?


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## retiredsparktech

Peter D said:


> I'm curious as to why this is the case. No 3 phase primary voltage available?


Why was this equipment installed in the first place, if there is no power source. 25 HP is a little large for a single phase VFD. If one is available is the service large enough to handle it.


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## kbsparky

Peter D said:


> I'm curious as to why this is the case. No 3 phase primary voltage available?


Nope. This is in a rural area, a corn field out in the middle of nowhere.

This system has been operational for many years using a tractor-mounted generator. He uses the same gen set for 3 different fields, irrigating one, then moving to the next, and so on. There are cord sets on the pump control box, and also the irrigation control that plug into the gen set.

The farmer is getting tired of hauling the generator around, buying fuel, engine maintenance, etc. I figure that would get O-L-D after a few years ....

The power company has single phase service out there, supplying a few houses across the road. They won't run 3 phase without costing a fortune, however.

So we are left to deal with using single phase, and trying to make it work.


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## JRaef

You need to do some serious consideration of how you are planning to get power to this. It might be worth considering the cost of getting 3 phase dropped from your utility.

VFD issues:


You cannot run multiple motors from one VFD _independently_, meaning they need to ALL turn on and off together by using the VFD, and they will all run at the same speed should you choose to take advantage of that. So a VFD does not make for a good SYSTEM phase converter, it's best used as a controller / phase converter for one motor at a time. That means buying VFDs for each motor. (although I have no idea what your entire system is doing here).
VFDs do not as a rule step up the voltage either. So you would have to get a transformer to step up your 240V to 480V single phase. Then you would need to use 480V VFDs that are capable of 1 phase input. Technically all are, but some do not allow it, because they have built-in phase loss protection that cannot be defeated. It's just something that you need to look out for if you go that route.
To use a VFD as a phase converter for a single motor, you must DOUBLE the size of the VFD to the motor size. Therefore for your 25HP irrigation pump, you must buy a 50HP 480V VFD. Then the NEC rules for supplying and powering a VFD call for a MINIMUM circuit size of 125% of the VFDs maximum rated input power, NOT the motor connected to it. A 50HP VFD is roughly 72A (maybe more), so that means the MINIMUM circuit size you can feed it with is 90A on the 480 side, which means 180A on the 240V side. That is JUST the irrigation pump so far. So as it relates to #1 above, this means you need a 50HP + a 5HP + (4) 1HP 480V VFDs.
RPC issues:


RPCs are a better solution to running multiple motors that will turn on and off independently of each other. But the drawback is energy efficiency, you are running an "idler" motor to make that single phase into 3 phase and that motor must run all of the time when anything else is running. So to power this system, you have approx. 30HP connected and if they ever all have to run at the same time, you will need probably a 50HP rated RPC which will likely have about a 10HP idler motor. That then means if you have to run only one of the 1/2HP motors, you will also be running a 10HP idler. It will be basically unloaded and not consuming MUCH power, but it will be consuming more than a VFD would.
You still will need the transformer, but with an RPC I would do the transforming on the 3 phase side because it would be a smaller cheaper transformer.
You have to make sure that the control panel power is taken from the "real" legs, not the manufactured leg. Not big deal usually, just something to be sure of.
You will need to buy essentially a 30HP 1 phase combination starter for the 240V side of the RPC, that means again, the circuit size will be around 150A. Make sure you have that much available in your 240V 1 phase service.
In either case, also make sure you account for voltage drop, it's a big deal at that kind of power level.


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## kbsparky

JRaef said:


> You need to do some serious consideration of how you are planning to get power to this. It might be worth considering the cost of getting 3 phase dropped from your utility....


 Not going to happen. Got 100 grand lying around? Didn't think so.



> ...RPCs are a better solution to running multiple motors that will turn on and off independently of each other. But the drawback is energy efficiency, you are running an "idler" motor to make that single phase into 3 phase and that motor must run all of the time when anything else is running. So to power this system, you have approx. 30HP connected and if they ever all have to run at the same time, you will need probably a 50HP rated RPC which will likely have about a 10HP idler motor....


We were considering using a 50 hp rated unit. So far so good.



> .... That then means if you have to run only one of the 1/2HP motors, you will also be running a 10HP idler. It will be basically unloaded and not consuming MUCH power, but it will be consuming more than a VFD would....


Not likely. Those motors control the wheels on the irrigation array, and have to all operate together. Otherwise, the array would get out of whack/sync. And THEY don't run unless you have the water pumping thru as well. They all have their own VFD's in the main control box, as each motor has to operate at a different rpm in order to keep the array aligned straight.



> ...You still will need the transformer, but with an RPC I would do the transforming on the 3 phase side because it would be a smaller cheaper transformer...


I figured as much. Wouldn't this also solve the problem of using the control power from any of the output legs as well?



> ...You have to make sure that the control panel power is taken from the "real" legs, not the manufactured leg. Not big deal usually, just something to be sure of....


Difficult to do once the 480 transformer is installed, no? All the controls require 480 Volts here.



> ...You will need to buy essentially a 30HP 1 phase combination starter for the 240V side of the RPC, that means again, the circuit size will be around 150A. Make sure you have that much available in your 240V 1 phase service....


We were planning on installing a separate 200 Amp service for this project.


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## micromind

Given the above new info, I would lean more toward a rotary phase converter. Feeding a 3ø VFD from the output of another VFD will almost certainly be trouble. 

If you use a 240 volt phase converter and a 240∆ to 480∆ transformer, it won't matter which two legs the controls are on. It will also balance the voltage better. 

A 200 amp 1ø service will do it, but just barely. 

Se if the POCO will connect a 480 1ø service. Around here they will. If so, see if the VFDs on the wheel drive motors will accept 1ø. They might, probably not though. 

The wheel drive VFDs will be the critical factor here. I don't think they'll accept 3ø power from another VFD. Possibly if there are both line and load reactors involved, but I'd need to see hard data from the manufacturer. They might however, accept DC power from the main VFD. You'd need to look into whether the main VFD will be able to supply DC and whether the smaller VFDs will accept it. Just because it has DC terminals doesn't mean it'll work though. 

I have a sneaky suspicion you'll be using a phase converter and a transformer.


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## JRaef

kbsparky said:


> ... They all have their own VFD's in the main control box, as each motor has to operate at a different rpm in order to keep the array aligned straight.


 Well that's new info. Most likely they may be 1HP drives on those 1/2HP motors, because on a lot of 480V VFDs, 1HP is the smallest they make. So that may allow you to consider just buying two VFDs, a 5HP for the booster and a 50HP for the pump. But in fact if the booster and the pump are always going to run together and you don't need to vary the speed of either on,you may be able to get away with a single 50HP VFD to run both. It's probably a toss up by way of cost.

You really have 480V controls? No control power transformer? Haven't seen that in years. But anyway, having the 3phase transformer won't really "cure" the ills of the manufactured leg that comes off of an RPC, the issues just pass right through. But the problems are worst for electronics and controls that use a Neutral, i.e. 120V off of a CPT, so if you don't have that. it might be fine.

If it were me, I'd go with the RPC. I love VFDs but sometimes they can create new problems that you didn't already have, and farmers are not big fans of electrical problems in my experience. They like things simple and clean.

Good luck. :thumbsup:


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## kbsparky

Yeah, I won't be needing to vary the speed of anything here. My idea to use a VFD came from a recent elevator job we did. The elevator had a 3 phase motor on it, but only required a single phase circuit to run the thing. The VFD had its own inverters built-in, and "made" the 3 phase from the input which was rectified into DC first, then back into the 3 phase AC. A battery back-up was also built in, allowing the elevator to return to the ground floor level in the event of a power failure. Such a system should be able to start with just about any voltage, and make its own output at whatever level it chooses.

It was a small VFD, but I figured they make `em in all sizes so why not explore the possibility here?

I will still inquire at my local supply house if they have anything that will do the job, and compare the hardware costs, etc.

I have an inquiry into the POCO about them providing single phase 480 Volt service, but I am not holding my breath. They would have to set another transformer, in order to provide that voltage. Don't know if they are willing to have 2 transformers sitting out there, when one would normally do.

The closest 3 phase is miles away, so that cost is prohibitive, otherwise this whole discussion would be moot. 

The farmer believes that even single phase power with the extra hardware will be preferable to his current routine, and at lower costs.

I figure we will have to install some sort of time-delay circuit to allow for the rotary phase converter to get up to speed before the pump and system kicks in. Probably will use a control transformer and small relay to do the job.

Finally, yes, all the controls require 480 Volts. I had to do a double-take on that as well. No neutral, no 120 Volts, etc.

I'll try to get some pix of that control box next time I'm out there .... :blink:


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## Jlarson

It pretty much be a no brainier for me. Farmers want no frills, cheap, and bulletproof. Defiantly a RPC w/ xformer job. A simple circuit to start the RPC first and shut it down last and all is well. 


On a side note, why the disbelief with 480 controls, it's like a weekly thing for me.


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## hardworkingstiff

I'm sure you know this, but I'll state it for those that are reading and might not know it. The 3rd leg created by the RPC must not feed the control circuit. It's only to be used for the motor.


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## alpha3236

The farmer is definately correct that this will save money. The cost of diesel being what it is. I do this type of work all the time and have found that roto phases take a lot of expensive replacement do to surges & lightning. I replace 5 or 6 a year. For the last couple of years I have been using a static/electronic unit from Phase Perfect and love them. They only come in a 240V configuration but they will supply the transformer for the boost to 480V & give you a great warranty. They also have intelligent people to talk to over the phone. The equipment's not cheap but gives a great install. As any of my customers that have replaced a roto phase can tell you, it's worth every penny. 
This is the only static type converter I know of that will handle variable loads, gauranteed. And the POCOs like them because starting a roto phase is a real line draw issue. Let me know how you make out, or if I can be of assistance.
www.phasetecnnologies.com


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## kbsparky

hardworkingstiff said:


> I'm sure you know this, but I'll state it for those that are reading and might not know it. The 3rd leg created by the RPC must not feed the control circuit. It's only to be used for the motor.


And how do you tell which is which, once it has been transformed up to 480 Volts?


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## Big John

kbsparky said:


> And how do you tell which is which, once it has been transformed up to 480 Volts?


 More to the point, once it's been transformed, why would it matter? Seems like it would simply appear as a very slight load on the derived phase, and I can't imagine that would be a problem.

-John


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## kbsparky

Exactly my point. An insignificant load if there was any at all....


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## kbsparky

alpha3236 said:


> ... Let me know how you make out, or if I can be of assistance.
> www.phasetecnnologies.com


Bad link.


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## MDShunk

Since the drives already exist in the control panel, and the control panel already exists, the only reasonable option (in my mind) is the rotary phase converter. If this was being designed from scratch (nothing existing but the motors), my opinion might be different. As it stands, get a rotary phase converter and call it a day.


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## hardworkingstiff

kbsparky said:


> And how do you tell which is which, once it has been transformed up to 480 Volts?


It is my understanding that the 3rd phase can be rather erratic. The 3-phase motors can handle it, but single-phase loads cannot. If you drove the transformer from the RPC, then wouldn't 2-phases be erratic instead of one? 

I would not drive a 3-phase transformer from the RPC, but rather drive the RPC after stepping up the voltage. Am I looking at this the wrong way, and if so, why?


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## Jlarson

A 3 phase transformer works just fine on the 3 phase side of an RPC.


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## hardworkingstiff

Jlarson said:


> A 3 phase transformer works just fine on the 3 phase side of an RPC.


Erratic/unbalanced voltage in doesn't have erratic/unbalanced voltage out?


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## Jlarson

You can't avoid that, even if you step up the single phase side to 480 the 3rd phase will be erratic. You're better off transforming the 3 phase side because of the difference in transformer size.


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## hardworkingstiff

Jlarson said:


> You can't avoid that, even if you step up the single phase side to 480 the 3rd phase will be erratic. You're better off transforming the 3 phase side because of the difference in transformer size.


But don't you then have to have a RPC rated at twice the HP + any transformer losses? The motor inrush will be harder on the RPC at the lower voltage than the higher voltage.

I understand the 3rd phase will be erratic, but by having it on the primary side of the transformer, don't you wind up with 2 erratic phases on the high side instead of 1?


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## alpha3236

Try http://www.phaseperfect.com sorry about that


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## micromind

If the transformer is 240∆ to 480∆, it really doesn't matter which two legs the controls are on. The reason being that a closed delta will tend to balance voltage at the expense of current. This is not an absolute dead-on balance, just a tendency. 

When a closed delta transformer is connected to an unbalanced system, there are circulating currents. Even if there's no load, there will still be measurable current in all 3 legs. These currents will all be of different magnitudes, and more importantly, different directions. This is because the delta connection is trying to balance all 3 voltages. 

If the transformer is Y-Y, then it'll simply pass the imbalance through. If it's ∆-Y or Y-∆, it'll try to balance, but not as much as a ∆-∆. 

This is why I'd recommend that the transformer be placed on the load side of the rotary converter.


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## micromind

alpha3236 said:


> Try http://www.phaseperfect.com sorry about that


This system actually looks good, provided the output is indeed a true sine wave. Not a pulse-width-modulated one. 

The reason I say this is because the OP is going to feed existing VFDs. They'll work on a true sine wave, but very likely not on a PWM one.


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## Jlarson

hardworkingstiff said:


> But don't you then have to have a RPC rated at twice the HP + any transformer losses? The motor inrush will be harder on the RPC at the lower voltage than the higher voltage.


Let's size the converter. 

1. largest single motor HP - 25, it's a well so it be considered a hard start load
2. total HP load - kinda had to pin down here but probably in the 30's 
3. go through manufacture sizing table, most recommend a 50 or 75 HP model for this load. 

Now if you connect it for 460 you divide the amperage ratings in half. HP is HP though. 





hardworkingstiff said:


> I understand the 3rd phase will be erratic, but by having it on the primary side of the transformer, don't you wind up with 2 erratic phases on the high side instead of 1?


No. Micromind covered it well in his post, although it really doesn't matter if you have an unbalanced leg because it won't effect line to line loads.


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## hardworkingstiff

JRaef said:


> ... But anyway, having the 3phase transformer won't really "cure" the ills of the manufactured leg that comes off of an RPC, the issues just pass right through...





micromind said:


> If the transformer is 240∆ to 480∆, it really doesn't matter which two legs the controls are on. The reason being that a closed delta will tend to balance voltage at the expense of current. This is not an absolute dead-on balance, just a tendency.


I'm so confused. :icon_confused::icon_confused:


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## Phasingout

*Phasingout*

I have been following this thread because it is a mirrored image of a project that I am currently involved with. My difference is that we are trying to power a 50HP/480volt 3ph motor with 240volt 1ph input. We too are thinking we need the 240/480v 1ph transformer before the phase converter,but we are getting conflicting opinions from motor shops as to the size (kva) of the transformer needed. They are concerned about the voltage drop issues (approx 1250ft) and the pf of the motor used. We are trying to decide also the fault current ratings for the power company and the size of transformer they need to supply. Has anyone done one this size and if so what transformer did you go with...and has there been any issues with motor integrity....interested to hear...


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## micromind

At 1250', a 50 HP 3ø motor operating at 480 volts would need anywhere from a 350 AL to a 750 AL depending on how hard the driven machine starts, assuming the RPC is at the source end. 

You'd also need a pretty good-sized 240 1ø service. 400 amps would do, I wouldn't go much smaller. 

The POCO might not allow across-the-lines starting of a 50 HP motor. Especially if it's fed by a 1ø source.


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## frenchelectrican

micromind said:


> At 1250', a 50 HP 3ø motor operating at 480 volts would need anywhere from a 350 AL to a 750 AL depending on how hard the driven machine starts, assuming the RPC is at the source end.
> 
> You'd also need a pretty good-sized 240 1ø service. 400 amps would do, I wouldn't go much smaller.
> 
> The POCO might not allow across-the-lines starting of a 50 HP motor. Especially if it's fed by a 1ø source.


 
I just don't know why I did miss this thread here so if you heard a " written pole motour " ?

If not I can post a link about that.

It simauir to sychronous motour.

So therefore here the link below.

http://www.precisepwr.com/single_phase_motors.asp?bhcp=1

That should help ya and I have done two allready it have alot of pluses but only single con is cost of the motour itself is more than convental triphase motour.

Note : I will post a second link which it is a M-G verison of written pole motour.

http://www.precisepwr.com/1to3converter.asp?bhcp=1


Merci,
Marc


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## Phasingout

*Phasingout*

The motor integrity and the voltage drop issues, along with the phase converter makeup is being supplied by the irrigation installer and so he is going to assume responsibility of any future motor failures. My concern is that I would supply his phase converter with the proper incoming voltage to make the incoming side up to par. We have a the motor shops agreeing that a 75kva transformer would be adequate, even though I was more comfortable with a 100kva. It also looks like the power co. is going with a 75kva also and a 320amp/240v 1ph service with a 225amp breaker dedicated to the secondary 240/480 transformer....seems marginal to me,but everyone says it will work fine...any thoughts


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## JRaef

Phasingout said:


> The motor integrity and the voltage drop issues, along with the phase converter makeup is being supplied by the irrigation installer and so he is going to assume responsibility of any future motor failures. My concern is that I would supply his phase converter with the proper incoming voltage to make the incoming side up to par. We have a the motor shops agreeing that a 75kva transformer would be adequate, even though I was more comfortable with a 100kva. It also looks like the power co. is going with a 75kva also and a 320amp/240v 1ph service with a 225amp breaker dedicated to the secondary 240/480 transformer....seems marginal to me,but everyone says it will work fine...any thoughts


Generally a 75kVA would be too small for my liking, but if it is only supplying this one motor, then the VD essentially acts like a Reduced Voltage Reactor starter. The problem is it will increase the acceleration time, which may be a problem for the pump especially if it uses the water pressure to lube the bearings. You need to check with the pump supplier to see if there is a maximum acceleration time, there usually is if it is a submersible. If so, you want the XFMR kVA to be at least 2.5x the motor HP to avoid significant VD.


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## garfield

Vfd for the pump and rotary for the rest of it. Best of both worlds and significant savings potential by slowing down the pump.


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## Phasingout

*Phasingout*

I think I will wait to see what his phase converter comes with and what ever aux. components he is supplying before I get too excited, I don't know how you guys feel when an equipment installer provides some essential electrical equipment with out knowing anything about it .....but my nerves get a little uneasy....we'll see


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## Phasingout

*Phasingout*

Fellas', this is the followup on the project concerning the 1phase input and the sizing of the disconnects for the 480volt conversion to 3phase. We installed a poco. 100KVA, 1phase transformer on pole, ran paralled 4/0 triplex to existing meter pole, we then paralled 4/0 to CT cabinet which then split to the existing meter service disconnect and also to new 400amp, 1phase, 240volt fuseable disconnect. The irrigation supplier provided a 75KVA, 1phase transformer with 240/480volt primary and 120/240 secondary (we ended up having to reverse xfmr to get proper input and output voltages) we fed the xfmr with paralled 3/0 copper with #2 grounding conductor (no neutral needed). We then came out the secondary side with 3/0 copper for our 480volt load and into a 200amp, 600volt disconnect, then ran #3/0 copper to the "A" section phase converter (40hp/3ph) and then #2 copper to 2nd phase converter ("B" section). The irrigation supplier trenched in #4/0 AL-quad urd, which was terminated in "A" section phase converter. The results were as follows: input voltage from power company was 124/248 1ph, so output from 75KVA transformer was 496volts, amperage load on 75KVA primary side on start up was an inrush of 322amps for 4 seconds and a constant amperage draw of 242amps with pump running. The amperage on 480v secondary side of 75KVA transformer was a constant 121amps. Phase converter motors were rated a 40deg.C continous and we were dealing with 95deg F. ambient temperatures We fused the 400amp safety switch with 350amp/240volt current limiting fuses and the 200amp safety swith with 200amp/600volt time delay fuses(we could have went a little closer to amperage draw but am concerned with drag at pump location). There was a total voltage drop of 50volts at 1250ft which was well within the perimeters from the motor shop, project passed state inspection with flying colors.......hopes this helps anyone with similar projects


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