# VFD loads running three phase pump off single phase power



## SWDweller (Dec 9, 2020)

Why does the actual load matter?

Lift station, water or waste? If there is a AHJ let them sort it out. Making changes tends to have issues later on when the problems start.

What is the environment? Inside or in the ambient? Depending on whose drives you use they can get pretty hot inside a NEMA 12 can hanging on a pole. 
IMO the 30 hp drive is bigger than it needs to be for a single motor.
Lift station tells me a lot of on and off for the motors. Hard service definitely. 
Better check the SES for the pumps, 150 amp breakers do not fit in every single phase load center or panel board.


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## backstay (Feb 3, 2011)

I thought it was 25-30 percent. At 30 you are under 25 hp.


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## BrisketTacos (Dec 2, 2021)

SWDweller said:


> Why does the actual load matter?
> 
> Lift station, water or waste? If there is a AHJ let them sort it out. Making changes tends to have issues later on when the problems start.
> 
> ...


Like I said, the plans are extremely vague, directing me to size the service to the pump requirements. This is a project for the Dept of Corrections at a local prison so there is no AHJ to speak of. I had originally planned on installing a 100 amp single phase 4x disconnect to feed the Lift Station Control Panel. (Panel is furnished by my utility contractor with his lift station package). I figured 100 amps based on the HP of the pumps and their stated FLA. Now that the project is going forward I get the submittals for the Control Panel and it's got a 400 amp main disconnect switch, two 150 amp breakers for two vfds plus a couple of 15 amp single poles for a service plug and controls. Corrections department engineer says based off the FLA of the pumps I'm good to go with 100 Amps but the 150 amp breakers for the VFDS is throwing me. I do know that you have to upsize the VFDs for single phase (I've seen between 1.73 x the motor rating to 2x mentioned as rough guides) I'm unclear on weather the VFDs are actually pulling more load than the pumps or are just oversized for derating purposes. I actually do a lot of lift stations and other municipal work and feel like I should know this but honestly this is the first time I've ever encountered this specific situation and it's aggravating me that I don't know the answer.


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## John Valdes (May 17, 2007)

Call the drive manufacturer and ask them. I bet they can tell you exactly what you want to know. Who builds these drives?


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## JRaef (Mar 23, 2009)

*SOME* VFD mfrs will tell you that the VFD amp rating must be at least 2x the motor FLA. Others will tell you that the VFD must be de-rated by 65% (motor FLA divided by .35), and still others will say you cannot do it at all. So as John says, you MUST get the de-rating information from whatever VFD mfr you will be using, and I suggest getting it *IN WRITING* from the mfr, not from a sales rep (who will tell you what you want to hear). I’ve seen numerous situations where people made ASSumptions based on what someone told them, only to find out the mfr would not cover it under warranty because THEY never said that.

That said, a 30Hp 230V VFD is likely rated for around 75-80A, 2x your motor FLA would be 85.2A, so there is no VFD I know of on the market that would allow that low of a de-rating.

Don’t guess unless you want to take on 100% of the warranty risk.


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## just the cowboy (Sep 4, 2013)

BrisketTacos said:


> I am doing a small lift station, the plans aren't very good (to say the least) and I have a question for you guys. Available power is single phase 120/240, specified pumps are 230V three phase 16.8 HP 42.6 FLA. The control panel drawings show VFDs rated for 30 hp motors fed from 150 amp two pole breakers. I know that you upsze a VFD when running three phase motors off single phase, my question is how do I determine the actual load on the VFD in this instance?


Here is the recommendation from Automation Direct on upsizing their drives. 
Some manufactures only say 2 times some say 3 times. Yours looks like they did 2 times the drive and only used 15HP.


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## BrisketTacos (Dec 2, 2021)

Thanks for the responses guys. I am following up with the manufacturer and going back at the engineers. I'll let ya'll know what I find.


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## Almost Retired (Sep 14, 2021)

BrisketTacos said:


> Thanks for the responses guys. I am following up with the manufacturer and going back at the engineers. I'll let ya'll know what I find.


starting to sound like the engineer may need to actually _design_ a set of plans


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## SWDweller (Dec 9, 2020)

If your working for the bureau of Prisons there are boiler plate specs for prisons. Been down the road twice for their work. 

Why don't you just get a 3 phase service for the pumps. I bet a bit of sweet taking to the POCO design engineer the amount of crap that you could be putting back on the lines, would make 3 phase very attractive.

Also the bureau has approved vendors for equipment. I would be surprised if Automation Direct made the list. 

I did a single phase 480 service through a Toshiba drive to get 3 phase. The machine said it was 3 phase but it was really 3 single phase heaters. (Made in France) I added a isolation transformer and got enough cushion for the heaters to work. Had help from some design engineers I know that work for Eaton. This was for a nunnery where they made communion crackers to keep the doors open. They had a rotary phase converter that could not be fixed.
The salesman who designed this project was pulled on the carpet and let go. Of course it was all my fault because there was some mystery solution that he would not provide to us. Did loose the cost of the transformer and wiring. 

I council you to start pushing back, bureau of prison's says backup generator to me. You just have not found it because of the invisible ink.


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## joe-nwt (Mar 28, 2019)

SWDweller said:


> If your working for the bureau of Prisons there are boiler plate specs for prisons. Been down the road twice for their work.
> 
> Why don't you just get a 3 phase service for the pumps. I bet a bit of sweet taking to the POCO design engineer the amount of crap that you could be putting back on the lines, would make 3 phase very attractive.
> 
> ...


It would save a lot of time if you create a list of things you haven't done.


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## gpop (May 14, 2018)

I have a bunch of lift stations running 3 phase from a single phase supply. 
Its possible to undersized the drive but its defiantly not recommended. Short run times, alternating pumps and the ability to drop a couple of hertz helps in a emergency when you do not have the correctly sized drive. (mechanical design specs normally have a lot of extra fluff built in so basically there's less inflow, head pressure. etc)

As yours is a new install it less to do with what the drive can do and more to do with the warranty so its back to the manufacturer for sizing.


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## paulengr (Oct 8, 2017)

BrisketTacos said:


> I am doing a small lift station, the plans aren't very good (to say the least) and I have a question for you guys. Available power is single phase 120/240, specified pumps are 230V three phase 16.8 HP 42.6 FLA. The control panel drawings show VFDs rated for 30 hp motors fed from 150 amp two pole breakers. I know that you upsze a VFD when running three phase motors off single phase, my question is how do I determine the actual load on the VFD in this instance?


1.732 times the FLA divided by VFD efficiency.

But you don’t need that. What you need is the name plate current rating, period. From the line side the VFD is the load, not the motor.

Do not forget 3 key issues: a single phase motor starter will tend to need maintenance in 10 years. The starting capacitor and/or potential relay usually croak about that time. It produces little heat and handles most real world environments well. It requires 3 leads for power plus 2 leads minimum for thermal protection and a moisture alarm although most have more wires. Replacing everything costs a couple hundred in parts. A VFD if it survives that long, lasts about 10 years. But they don’t like dust, grass seeds, heat, and especially sewer gases. All of these lead to a shortened life. It will cost hundreds to thousands to replace. So why put them in lift stations when everything points to going with a simple level control design with basic pumps, even if they are single phase?

Trust me I despise working on single phase motors too but in this application it’s the way to go.

As far as low on details, you have everything. Lift stations are one of the few controls where you can just buy prepackaged controls for cheap.


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## gpop (May 14, 2018)

paulengr said:


> 1.732 times the FLA divided by VFD efficiency.
> 
> But you don’t need that. What you need is the name plate current rating, period. From the line side the VFD is the load, not the motor.
> 
> ...



common sense left the waste water business years ago. The panels we use start at 60k.

Vfd's add a air-conditioner, A back up transfer switch, plc, hmi, radio, surge protection, more surge protection, gas detector, auto meggers, bunch of other junk then wrap it in a 316 SS cabinet for 80k. Chuck in another 50k for pumps and 20k for the hardware and your well on the way to 250k.


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## paulengr (Oct 8, 2017)

gpop said:


> common sense left the waste water business years ago. The panels we use start at 60k.
> 
> Vfd's add a air-conditioner, A back up transfer switch, plc, hmi, radio, surge protection, more surge protection, gas detector, auto meggers, bunch of other junk then wrap it in a 316 SS cabinet for 80k. Chuck in another 50k for pumps and 20k for the hardware and your well on the way to 250k.


I hear you on some of it. You can’t fix stupid. Some of the improvements are true improvements. Going to ultrasonic and now radar level sending is fantastically better than floats. Most just leave one high level float and call it a day. As far as PLCs sure a small proprietary level controller is cheaper and simpler but documentation is hard to come by and those companies come and go. When you can buy a decent PLC that does everything for a couple hundred it’s the same price as the old controllers.

Don’t forget that I look at a lift station as $10,000 per pump every 10 years in maintenance costs, without electrical.


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## just the cowboy (Sep 4, 2013)

SWDweller said:


> If your working for the bureau of Prisons there are boiler plate specs for prisons. Been down the road twice for their work.
> 
> Why don't you just get a 3 phase service for the pumps. I bet a bit of sweet taking to the POCO design engineer the amount of crap that you could be putting back on the lines, would make 3 phase very attractive.
> 
> ...


AD was just an example


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## LGLS (Nov 10, 2007)

BrisketTacos said:


> Like I said, the plans are extremely vague, directing me to size the service to the pump requirements. This is a project for the Dept of Corrections at a local prison so there is no AHJ to speak of. I had originally planned on installing a 100 amp single phase 4x disconnect to feed the Lift Station Control Panel. (Panel is furnished by my utility contractor with his lift station package). I figured 100 amps based on the HP of the pumps and their stated FLA. Now that the project is going forward I get the submittals for the Control Panel and it's got a 400 amp main disconnect switch, two 150 amp breakers for two vfds plus a couple of 15 amp single poles for a service plug and controls. Corrections department engineer says based off the FLA of the pumps I'm good to go with 100 Amps but the 150 amp breakers for the VFDS is throwing me. I do know that you have to upsize the VFDs for single phase (I've seen between 1.73 x the motor rating to 2x mentioned as rough guides) I'm unclear on weather the VFDs are actually pulling more load than the pumps or are just oversized for derating purposes. I actually do a lot of lift stations and other municipal work and feel like I should know this but honestly this is the first time I've ever encountered this specific situation and it's aggravating me that I don't know the answer.


I'm sorry,,, is this "Dept. of Prisons" is an actual "Authority???" Not subject to the laws of physics or mandated adopted codes???

Here in NY this has to be an "Authority" such as... Port Authority, Schools construction AUTHORITY and Bridge & Tunnel AUTHORITY, in order to WRITE your own codes and then ENFORCE them and NOT be subject to what the commoners are,,, or inspections OUTSIDE of that "Authority." Or "Metropolitan Transportation AUTHORITY." They can write their own rules standards and answer to NO ONE and NOTHING and NOBODY. 
,
Much in the same way "The Vatican" is a autonymous country" within ROME Italy... 

So our "department of corrections" is just that, as you referred to your's... a "_department_ of... corrections..." not a legitimate "*Authority*" and therefore you follow NEC unless your area is not abiding by NEC at all.


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## paulengr (Oct 8, 2017)

LGLS said:


> I'm sorry,,, is this "Dept. of Prisons" is an actual "Authority???" Not subject to the laws of physics or mandated adopted codes???
> 
> Here in NY this has to be an "Authority" such as... Port Authority, Schools construction AUTHORITY and Bridge & Tunnel AUTHORITY, in order to WRITE your own codes and then ENFORCE them and NOT be subject to what the commoners are,,, or inspections OUTSIDE of that "Authority." Or "Metropolitan Transportation AUTHORITY." They can write their own rules standards and answer to NO ONE and NOTHING and NOBODY.
> ,
> ...


“Authorities” would be what we call joint ventures or subsidiaries in private business. For instance if multiple municipalities combine their water systems or if say the state/county is operating a port which is effectively a business but it’s on public land for public use. These are all totally legitimate. The issue with “authorities” is when they start doing things that may even be within their charter but are beyond what the “owner” intended, same problem private business has with joint ventures and subsidiaries. The level of corruption can get just as bad.

Prisons are not bad places to work. Just take your labor hours estimate and double it. Don’t be there at certain times of the day (roll call). Accept their rules for what they are and work with them. Prison financing for maintenance departments recognizes they have tons of almost free labor.


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## LGLS (Nov 10, 2007)

paulengr said:


> “Authorities” would be what we call joint ventures or subsidiaries in private business. For instance if multiple municipalities combine their water systems or if say the state/county is operating a port which is effectively a business but it’s on public land for public use. These are all totally legitimate. The issue with “authorities” is when they start doing things that may even be within their charter but are beyond what the “owner” intended, same problem private business has with joint ventures and subsidiaries. The level of corruption can get just as bad.
> 
> Prisons are not bad places to work. Just take your labor hours estimate and double it. Don’t be there at certain times of the day (roll call). Accept their rules for what they are and work with them. Prison financing for maintenance departments recognizes they have tons of almost free labor.


OK well In NYS any "Authority" well... not "Sports Authority" lol is a quasi-government within a government... so the NYS thruway Authority can write it's own codes, sell and buy financing bonds... and is governed by a few different schemes the most common one being a couple people from the State, a couple from the local municipality it's operating in, and 1 tiebreaker assigned by a district court judge. Then they can condemn lands... like the thruway authority... design and build their own works... and have NO other overruling body to govern or control them, influence them or have a conflict of interest with... a political beef etc...


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## paulengr (Oct 8, 2017)

LGLS said:


> OK well In NYS any "Authority" well... not "Sports Authority" lol is a quasi-government within a government... so the NYS thruway Authority can write it's own codes, sell and buy financing bonds... and is governed by a few different schemes the most common one being a couple people from the State, a couple from the local municipality it's operating in, and 1 tiebreaker assigned by a district court judge. Then they can condemn lands... like the thruway authority... design and build their own works... and have NO other overruling body to govern or control them, influence them or have a conflict of interest with... a political beef etc...


Not trying to hijack the thread..,

From what I understand North Carolina is different from most states. In North Carolina municipalities are extensions of state government. They are not independent. Neither are authorities. So they are subject to NC building codes for instance, currently 2020 NEC with minor editing. Most of them have no more than a half dozen local ordinances. Counties have somewhat more autonomy but they are rarely a hot bed of politics.


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## LGLS (Nov 10, 2007)

paulengr said:


> Not trying to hijack the thread..,
> 
> From what I understand North Carolina is different from most states. In North Carolina municipalities are extensions of state government. They are not independent. Neither are authorities. So they are subject to NC building codes for instance, currently 2020 NEC with minor editing. Most of them have no more than a half dozen local ordinances. Counties have somewhat more autonomy but they are rarely a hot bed of politics.


Well in NYS each county is actually more like a state like the united stats states make up a country, each pretty autonoymous. We don't have "state" schools for k-12, they're local even within the counties and towns they serve... there's 135 separets boards of educations and school districts each with it's own "Board of standards and appeals" although must still meet state guidelines and "mandates" involving course offereings... A township sets it's own codes or adopts the NEC at face value... not the County (Some areas call counties Twps or "Parishes.") But not the State... State just sets what level every bar shall be placed at...


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## paulengr (Oct 8, 2017)

LGLS said:


> Well in NYS each county is actually more like a state like the united stats states make up a country, each pretty autonoymous. We don't have "state" schools for k-12, they're local even within the counties and towns they serve... there's 135 separets boards of educations and school districts each with it's own "Board of standards and appeals" although must still meet state guidelines and "mandates" involving course offereings... A township sets it's own codes or adopts the NEC at face value... not the County (Some areas call counties Twps or "Parishes.") But not the State... State just sets what level every bar shall be placed at...


Schools are county wide generally and similar to what you describe but the subject was prisons and “authorities”. Electric codes are state wide with exceptions. Raleigh has their own (more restrictive) code as does Cary and Durham. The rest don’t change it. State government follows NEC. Outside of those areas ports, airports, mines, utilities, and hospitals are all different and vary a little from NEC. But that’s true anywhere. For mining I made a 2 page list of all the mining electrical regulations for surface mines. Most generally follow NEC. Underground is a bit more tricky.


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## BrisketTacos (Dec 2, 2021)

Thought I would give y'all an update on this project. The Engineers for the department of corrections have dug in and are falling back on the language on the plans ccalling for us to "size service according to the proposed equipment requirements". My employer has taken the stance that we are not engineers and that they need to "engineer" the service requirements. This is all coming to a head next Thursday at a meeting with all perties. Should be fun.
What surprises me about all of this is that no-one seems to have any idea what the load will be on these VFDs running three phase pumps off of single phase service, other than a vague statement about doubling the size of the VFDs. My next step is calling the manufacturer of the VFDs to see if they can tell me what the load on the VFDs will be based off the pump size.
I will update this as it continues to develop and anyone is interested.


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## Almost Retired (Sep 14, 2021)

yes please !!


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## paulengr (Oct 8, 2017)

BrisketTacos said:


> Thought I would give y'all an update on this project. The Engineers for the department of corrections have dug in and are falling back on the language on the plans ccalling for us to "size service according to the proposed equipment requirements". My employer has taken the stance that we are not engineers and that they need to "engineer" the service requirements. This is all coming to a head next Thursday at a meeting with all perties. Should be fun.
> What surprises me about all of this is that no-one seems to have any idea what the load will be on these VFDs running three phase pumps off of single phase service, other than a vague statement about doubling the size of the VFDs. My next step is calling the manufacturer of the VFDs to see if they can tell me what the load on the VFDs will be based off the pump size.
> I will update this as it continues to develop and anyone is interested.




This is a basic case of RTFM. Read The blanking Manual. It spells it out. AB has an entire book just on VFD wiring.

Go ahead but I can tell you that you’re barking up the wrong tree:. The ground cable size will be in the VFF manual/. A VFD cannot serve line to neutral loads unless it is a very unusual type like matrix or NPC. However it does generate significant common mode voltage so often the ground will carry a lot of current. Tested one Wednesday with 7 A load and 0.7 A current through the ground. 7.5 HP 230 V.

All VFDa have specific grounding requirements like a mandatory stranded EGCS. This sometimes leads to the EGCS bigger than the phase conductors. NEC says it should not be bigger.

On the line side you will see a label showing the rated amps. That is the “loaf” as far as NEC is concerned. Ground beef NEC rules which is based on that number and the feeder size.

The law says the buck stops with the EC, not the engineers. If they mess it up you are responsible.


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## Yankee77 (Oct 5, 2020)

paulengr said:


> This is a basic case of RTFM. Read The blanking Manual. It spells it out. AB has an entire book just on VFD wiring.
> 
> Go ahead but I can tell you that you’re barking up the wrong tree:. The ground cable size will be in the VFF manual/. A VFD cannot serve line to neutral loads unless it is a very unusual type like matrix or NPC. However it does generate significant common mode voltage so often the ground will carry a lot of current. Tested one Wednesday with 7 A load and 0.7 A current through the ground. 7.5 HP 230 V.
> 
> ...


... yet it’s illegal to vary off a P.E. stamped set of drawings, you sure
?


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## paulengr (Oct 8, 2017)

Yankee77 said:


> ... yet it’s illegal to vary off a P.E. stamped set of drawings, you sure
> ?


It’s illegal to violate Code for a licensed electrician, regardless of PEs drawings. Unless you are out of scope (see the very first section of Code) or on federal land Code is law. There are areas in NEC where a PE can provide alternatives to what the Code requires but if what they say contradicts Code, Code wins. EC is held to Code, no matter what PE scribbles and stamps.

PE drawings amount to engineering. This is where the law gets stupid. EC must follow Code. PE does engineering (design). So ultimately If Code calls for say 1/0 and PE states #1 EC cannot install as specified. So you stop work.


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