Sizing Generator for Submersible Well Pump

[EdwardB]

I know there has been a long thread on this a few years ago, but I still have some confusion. I have a 5hp 240V single phase Franklin submersible well pump with a starter box. It is wird to a 30 amp breaker in my panel. I am trying to determine the minimum size generator to safely run this during outages. I emailed Franklin, and here was their response:

The 5 HP Franklin Electric motor that powers your pump, and I am assuming it is single phase draws 27.5 full load amps and requires a 60 amp breaker or if you have a dual element fuse it should be rated at 30 amps. A consideration when sizing a generator is that upon start up, for less than a second of time, the motor has a locked rotor amp draw of 121.0 that will trip some generators overload.

Here is a picture of the starter box: https://www.dropbox.com/s/tcj22kztihnc29r/WellStarter.JPG

Here is a link to a Franklin guide; page 5 references generator sizing: https://www.dropbox.com/s/9o4dsbzou5hrilc/FranklinSubmersibleMotorGuide2010.pdf

The suggested generator info in the brochure seems way more than the other information would imply. Any help would be appreciated.

 

[Dave M7040]

Perhaps this is a stupid question but why do you have such a large well pump. Most residential installations are fractional horsepower units, 1/2 or 3/4?
If you dont need this big a pump you could change the pump, buy a much smaller generator,and have $ left over.
Dave M7040

 

[EdwardB]

I also use the well for irrigation purposes.

 

[mbohuntr]

You can easily draw 300% of FLA when starting a motor. There is also a much higher inrush current that can trip a breaker. Industrial breakers use more sophisticated circuitry to trip at higher currents than that to protect from transient inrush currents in the hundreds or thousands of amps. They have adjustable trip settings on their faces to customize their protections.
We had to have an electrical engineer calculate the new settings for us to back feed a three phase transformer that kept tripping for that reason. When the normal power was restored, we reset the settings. I don't have any experience in generators, but it seems reasonable.

 

[EdwardB]

Where I am confused is that the breaker in the panel is just a standard 30amp breaker. It seems like it would trip if the well were really drawing that much current. The box info also confuses me. Maybe it has some "soft start" capacitors or the like?

 

[mbohuntr]

The generator has it's own internal breaker that will trip.

 

[mbohuntr]

A generator will have a second rating for "surge" amps. My 5k generator has a surge rating of something like 5800..... you must remember, When a device pulls more current than the gen can produce, the voltage will temporarily drop and the current shoots up before the generators engine can respond.

 

[daybreak1998]

Howdy,
At least you have taken the correct steps to figure things out. Researching the manufacturers recommendations is a important part. Yes, I would say that your control box has the added wizardry for soft start. When someone talks about a 5hp motor on a farm, it is a good size load for starting and running. Since you say its for irrigation, you then have tractors as well. Since this is all wired into your system, you will need to think about how it will all connect into your panel. Some questions below.
1. what is your service? type? (pole top, underground, separate meters)
2. distance from panel to this pump control box? Do you have a smaller panel in your pump house?
3. how many times do you lose power?
4. do you have any other wells on the farm?
5. besides powering the well, what other power things do you want to run? do you want to run it all at the same time? or run the 5hp pump, then shut that breaker off and run everything else?

self contained mounted genset system, open inside genset system, pto generator system?

 

[buickanddeere]

There are Franklin variable frequency drive boxes for three wire single phase and three phase well pumps. A storage tank is used to hold pressure during no and low flow. During mid, high to max water demand. The pump drive box varies the pump motor rpms to maintain a system pressure of your choice.
These VFD also provide an soft start capability.
My 3/4HP 240V well pump drags my 5500 run/8500W start Generac low enough to trip off some household electronic devices and dim the lights to reddish colour.
To start a 5HP single phase pump motor. You need a minimum of a 20Kw pto powered generator with a 30 pto HP tractor .
I don't know how the 30amp breaker isn't tripping unless there is a VFD already on the pump. A 5HP 240V motor in the code book needs a 70 amp breaker.

 

[EdwardB]

There are Franklin variable frequency drive boxes for three wire single phase and three phase well pumps. A storage tank is used to hold pressure during no and low flow. During mid, high to max water demand. The pump drive box varies the pump motor rpms to maintain a system pressure of your choice.
These VFD also provide an soft start capability.
My 3/4HP 240V well pump drags my 5500 run/8500W start Generac low enough to trip off some household electronic devices and dim the lights to reddish colour.
To start a 5HP single phase pump motor. You need a minimum of a 20Kw pto powered generator with a 30 pto HP tractor .
I don't know how the 30amp breaker isn't tripping unless there is a VFD already on the pump. A 5HP 240V motor in the code book needs a 70 amp breaker.

My system uses a pressure tank like you describe. Did you see the attached picture of my control box? I'm not sure that it is a VFD, but it must work some magic because it is only on a 30A breaker.

 

[EdwardB]

Howdy,
At least you have taken the correct steps to figure things out. Researching the manufacturers recommendations is a important part. Yes, I would say that your control box has the added wizardry for soft start. When someone talks about a 5hp motor on a farm, it is a good size load for starting and running. Since you say its for irrigation, you then have tractors as well. Since this is all wired into your system, you will need to think about how it will all connect into your panel. Some questions below.
1. what is your service? type? (pole top, underground, separate meters)
2. distance from panel to this pump control box? Do you have a smaller panel in your pump house?
3. how many times do you lose power?
4. do you have any other wells on the farm?
5. besides powering the well, what other power things do you want to run? do you want to run it all at the same time? or run the 5hp pump, then shut that breaker off and run everything else?

self contained mounted genset system, open inside genset system, pto generator system?

My "farm" is just as a hobby. About 60 fruit trees, some blueberries and raspberries, lawn sprinkling and a big garden. Everything runs off of the one well which is wired into the house electrical panel. I don't lose power much and can run what I need on a small generator; except for the water well (I think, haven't tried yet). That gets old in a hurry with five kids, though. I plan on filling the pressure tank and then shutting off the well. I don't need the whole house powered and am content to flip some breakers to save money on a larger genny. If have to go bigger than my 7,500W continuous 9,500W peak portable unit; then I probably will get a PTO unit for the JD.

 

[hr3]

Here is a chart,, SIZING A GENERATOR FOR ELECTRIC MOTOR LOADS

 

[buickanddeere]

There is something odd going on with that 30amp breaker. There is no way a working 30amp breaker won't trip starting a well pump of that size. With just a standard across the line starter.
That breaker is likely failed internally and is offering no protection. The main electrical service breaker maybe the only short circuit protection to the pump.
It's cheap insurance to obtain and install a new 70amp breaker that works.
I snagged a new Franklin VFD box cheap on ebay for my well pump but alas. The box is for a three wire pump and the cheapskate that installed the well used a two wire pump.

 

[jaotguy]

maybe tackle this from another angle .... how deep is it to the water table ? how big is the well casing ?

you may be able to drop a jet pump injector and smaller lines down beside the existing pipe and use a much smaller 1/2 or 3/4 HP pump to get water as a backup system to refill the water tank, and using a smaller generator .... yes it will take longer to "fill and pressurize" but at least you have water and it won't take specialty equipment..... $$$$$$

 

[C4Ranch]

Are you positive it's 5hp? You must be getting unbelievable gpm/pressure. With that power, you must be filling your pressure tank in seconds.

If you already have a gen, why not give it a try? I would like to do the same so I'm also interested in what you find out.

 

[TheGoose]

Here is the chart from Franklin. Google Franklin AIM manual page 5.

http://www.franklin-electric.com/aim-manual/page-5.aspx

 

[buickanddeere]

There is a real possibility that the well has a 5HP couple coupled to a 3HP motor. That could explain the 5HP starter and the motor operating from a 30 amp breaker.
For motors with thermal protection such as this pump. The breaker's only role is to interrupt short circuit events.
I have a 3HP 15FLA 240V Campbell and Hausfeld air compressor. A compressor rated motor with large starting cap and a compressor unloader. I tried plugging it into a 12/2 20amp 240V supply for the heater in the garage just out of curiosity. To my surprise it has operated for years ( without the heater) and has never tripped the breaker ?
One of these days when I get around to installing a breaker panel with more circuits. There will be a pony panel also installed in the garage to supply some dedicated tool receptacles.

 

[nc redneck]

I have a 3/4 hp well pump 260 feet deep. Also a 18 KW whole house gen set. I know from sound of gen set starting the pump is a pretty good sized load. Only other load you can actually hear is AC system.

 

[EdwardB]

Here is the chart from Franklin. Google Franklin AIM manual page 5.

Page 5 | AIM Manual | Franklin Electric

Hi Goose. That was the manual that I found online as well. It says 7,500W internally regulated and 15,000W externally regulated. Guess I need to do some research on that, since I don't know what the difference is. I've also got a call into Franklin.

 

[EdwardB]

Are you positive it's 5hp? You must be getting unbelievable gpm/pressure. With that power, you must be filling your pressure tank in seconds.

If you already have a gen, why not give it a try? I would like to do the same so I'm also interested in what you find out.

Yep, its a 5HP. I need the GPM for irrigation, and, yes, it does fill the pressure tank pretty quickly; but it doesn't cycle the pump enough to be detrimental to the motor. Once I get more info, I may try my 7,500W, 9,500W peak unit.