# 20HP Single phase motor



## spinninwheels (Oct 28, 2012)

I have a client interested in getting a new service (200A). He has some 3phase equipment he wants to operate.

He eventually wants to install a 20HP single-phase motor to operate a phase converter, so that he can operate this equipment.

He hasn't provided me with any motor specs.

He was under the impression that this motor would be pulling ~60A.

I'm thinking a VFD might be more prudent.

So with a 20hp motor with the FLA ~100A, what range of inrush current would be expected?

Hydro usually installs a 25kVA can.

I see there being some potential issues.

TIA


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## emtnut (Mar 1, 2015)

For Hydro around here, you need approval from them for a motor that size.


5hp and up, a 'Hydro' approved reduced voltage starter.
>10hp, special approval
*edit* that is for single phase service.



I'd start with a call to them.


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## CWL (Jul 7, 2020)

A 20hp single phase motor to run a phase converter? Or do you mean a 20hp three phase motor to be used as a phase converter? We built some phase converters out of 25 or so horsepower three phase motors once, but they were spun up to speed with a small 120V motor on a belt drive before power was applied to the larger motor. One of the guys had a lathe, mill, bandsaw, drill press, and a hydraulic shear. Voltage readings improved as more equipment came on line untill the total amp draw exceeded the service from his house to the garage.


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## spinninwheels (Oct 28, 2012)

emtnut said:


> For Hydro around here, you need approval from them for a motor that size.
> 
> 
> 5hp and up, a 'Hydro' approved reduced voltage starter.
> ...


Yes, I've already reached out to them. I had a very brief convo with the Designs guy from Hydro, and he did say something about the engineering dept. But nothing specific, as this is early days.


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## spinninwheels (Oct 28, 2012)

CWL said:


> A 20hp single phase motor to run a phase converter? Or do you mean a 20hp three phase motor to be used as a phase converter? We built some phase converters out of 25 or so horsepower three phase motors once, but they were spun up to speed with a small 120V motor on a belt drive before power was applied to the larger motor. One of the guys had a lathe, mill, bandsaw, drill press, and a hydraulic shear. Voltage readings improved as more equipment came on line untill the total amp draw exceeded the service from his house to the garage.


The former.

I'm thinking it's cheaper to buy new equipment that isn't 3 phase.


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## 460 Delta (May 9, 2018)

A 20 HP motor, single phase, will have to be a Written Pole won’t it?


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## JRaef (Mar 23, 2009)

460 Delta said:


> A 20 HP motor, single phase, will have to be a Written Pole won’t it?


That's the only ones I have ever seen that big. Commercial Off the Shelf single phase motors generally top out at 10HP.


But if the goal is to make an RPC (Rotary Phase Converter), then you would have a 20HP 3 phase motor as the base unit. Applying power to it would LOOK like a 20HP single phase motor to the service though, and that would be in the neighborhood of *94A FLC* (54A x 1.732) draw *from the single phase source*, so around 560A starting current. It's going to be difficult to get that started off of a 25kVA can...


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## CWL (Jul 7, 2020)

JRaef said:


> That's the only ones I have ever seen that big. Commercial Off the Shelf single phase motors generally top out at 10HP.
> 
> 
> But if the goal is to make an RPC (Rotary Phase Converter), then you would have a 20HP 3 phase motor as the base unit. Applying power to it would LOOK like a 20HP single phase motor to the service though, and that would be in the neighborhood of *94A FLC* (54A x 1.732) draw *from the single phase source*, so around 560A starting current. It's going to be difficult to get that started off of a 25kVA can...


What would the starting current look like on the motor if it was already at speed from a small motor before power was applied? We used small motor to spin the 3PH motor being used as the converter up to speed before power was applied from the 1PH 240V. I don't remember any inrush current draw other than when the equipment fed from the converter was started. It's been quite a few years though, so my memory could be faulty.


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## Cow (Jan 16, 2008)

20hp single phase??? What could go wrong?


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## just the cowboy (Sep 4, 2013)

Again someone buying "equipment at a deal".

You need to find out what size 3 phase motors are on the equipment he wants to run?
Does he need more than one at a time.
Sounds like he needs a fuel phase converter to me.

Cowboy


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## 460 Delta (May 9, 2018)

JRaef said:


> That's the only ones I have ever seen that big. Commercial Off the Shelf single phase motors generally top out at 10HP.
> 
> 
> But if the goal is to make an RPC (Rotary Phase Converter), then you would have a 20HP 3 phase motor as the base unit. Applying power to it would LOOK like a 20HP single phase motor to the service though, and that would be in the neighborhood of *94A FLC* (54A x 1.732) draw *from the single phase source*, so around 560A starting current. It's going to be difficult to get that started off of a 25kVA can...


I’ve seen a 15 HP single phase somewhere,(it’s been a while, can’t remember where) but it was a behemoth that really didn’t have a standard size frame. It had a huge capacitor box on top. Probably enough uf to correct PF at a steel mill.


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## just the cowboy (Sep 4, 2013)

Baldor make a 15 single phase motor as a TEFC model as a standard size.


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## TechyWalla (Apr 6, 2020)

I would think that the simplest if it is 3ph equipment is to look into VFD's fed by 1ph.
In most case, the 3ph is for motors, any control may be able to be fed from a 1ph circuit.
If this is a industrial purposes, where is he operating out of?
His house?
T.W.


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## spinninwheels (Oct 28, 2012)

just the cowboy said:


> Again someone buying "equipment at a deal".
> 
> You need to find out what size 3 phase motors are on the equipment he wants to run?
> Does he need more than one at a time.
> ...


It may be one or two machines, I can't remember. The conversation started with, I need a 200A service. All the other information began to come out at a subsequent visit.

He has more loads to justify the new service, ie: new shop and another separate outbuilding. It was the mentioning of the 20HP motor that got my attention. He was very casual about it.

Obviously, some reduced voltage/soft start is a must. Even then, will a 200A service suffice? The prohibitive cost jump to a 400A service may make him rethink his 3phase machine(s).

At minimum, is this not a 400A with a 75kVA can?


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## spinninwheels (Oct 28, 2012)

TechyWalla said:


> I would think that the simplest if it is 3ph equipment is to look into VFD's fed by 1ph.
> In most case, the 3ph is for motors, any control may be able to be fed from a 1ph circuit.
> If this is a industrial purposes, where is he operating out of?
> His house?
> T.W.


It will be a new shop.


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## spinninwheels (Oct 28, 2012)

Hydro just got back to me.

They said the client would need to hire an engineering consultant.

They also said they can't mandate a main switch size. But after a main switch is proposed with an ESI (Electrical Service Information), Hydro Designs would look at it and let them know if they see any potential issues.


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## emtnut (Mar 1, 2015)

spinninwheels said:


> At minimum, is this not a 400A with a 75kVA can?



More than likely 400A with 100kVA , and that's if Hydro can do it depending on where he is.


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## JRaef (Mar 23, 2009)

CWL said:


> What would the starting current look like on the motor if it was already at speed from a small motor before power was applied? We used small motor to spin the 3PH motor being used as the converter up to speed before power was applied from the 1PH 240V. I don't remember any inrush current draw other than when the equipment fed from the converter was started. It's been quite a few years though, so my memory could be faulty.


A "pony motor" start scheme (which is what that's called) does not change the size of the spike in current, only the duration. So instead of it being a few seconds, it might be under a second. That can help.


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## spinninwheels (Oct 28, 2012)

emtnut said:


> More than likely 400A with 100kVA , and that's if Hydro can do it depending on where he is.


Actually, the can would be on a three phase pole.

But to drop 3 phase, pole needs to be changed from a 45' to a 50' (Hydro spec) plus the cost of 3 phase cans/rack (which I think they charge $15K).

I think he should sell his 3phase equipment and get single phase.


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## oliquir (Jan 13, 2011)

tell your client to get a 3ph generator, it would cost less money and he can run it only when needed or change all equipment to single phase


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## TechyWalla (Apr 6, 2020)

I think a few more details and machine specifics are needed in order to give an informed decision.
There are too many variables.
T.W.


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## spinninwheels (Oct 28, 2012)

TechyWalla said:


> I think a few more details and machine specifics are needed in order to give an informed decision.
> There are too many variables.
> T.W.


I agree. That will be at a later visit.


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