Sizing Generator for Submersible Well Pump

[EdwardB]

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.

I'm not sure, the 30A breaker has been there since Day 1 and it was installed by someone who knows what they are doing; so I think something else must be going on. I got this response from an electrician who deals with generators on another forum, referring to the info from Franklin:

"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 (this means 120 volts) or if you have a dual element fuse it should be rated at 30 amps." (would be 13.7 amps @ 240) is how i read their response

 

[grsthegreat]

Personally i have installed many many generators over the years.....im installing 2 more next week.... and i have the MOST problem with wells. The name plates dont mean anything. as the motors age, the start to pull more amps. So even if generator works with it last year, it may trip the circuit this year.....seen that happen lots of times.

A WAY cheaper solution would be to install a 250 - 500 gal underground storage tank that feeds the house. This is set between main well and house, and water just flows thru it until you need to turn on the generator....Inside this tank install a 1/2 - 3/4 HP pump to feed the house. You may have to install some shutoff valving to be used when the generator is being used. Heck, ive had some clients that have installed 5,000 gal poly tanks cause there preppers.

 

[westcliffe01]

EdwardB

Just doing the math, 30A x 240V = 7.2kW Dividing by 0.745699872 gets just less than 10hp. However, since this is a suddenly applied load, usual rule of thumb is 50-100% more to reliably start a load like that. Otherwise the motor would generally not be able to respond fast enough to hold RPM. Particularly true of todays high rpm lightweight generators.

I was not able to open the PDF that you posted but found this published info: Guidelines for using generators with submersible well pumps
Going with that, a 5hp electric motor shows a requirement from 15-18.85kW generator (externally regulated) or 7.5-9.4kW (internally regulated)

Here the text from the article:

"Use of Engine Driven Generators - Single-Phase or Three-Phase

Page 5 | AIM Manual | Franklin Electric

Table 5 lists minimum generator sizes based on typical 80 ï½°C rise continuous duty generators, with 35% maximum voltage dip during starting, for Franklinç—´ threewire motors, single or three-phase.

This is a general chart. The generator manufacturer should be consulted whenever possible, especially on larger sizes.

There are two types of generators available: externally and internally regulated. Most are externally regulated. They use an external voltage regulator that senses the output voltage. As the voltage dips at motor start-up, the regulator increases the output voltage of the generator.

Internally regulated (self-excited) generators have an extra winding in the generator stator. The extra winding senses the output current to automatically adjust the output voltage.

Generators must be sized to deliver at least 65% of the rated voltage during starting to ensure adequate starting torque. Besides sizing, generator frequency is important as the motor speed varies with the frequency (Hz). Due to pump affi nity laws, a pump running at 1 to 2 Hz below motor nameplate frequency design will not meet its performance curve. Conversely, a pump running at 1 to 2 Hz above may trip overloads.

Generator Operation

Always start the generator before the motor is started and always stop the motor before the generator is shut down. The motor thust bearing may be damaged if the generator is allowed to coast down with the motor running. This same condition occurs when the generator is allowed to run out of fuel.

Follow generator manufacturers recommendations for de-rating at higher elevations or using natural gas."

 

[westcliffe01]

Looking at your options, if you went with a 240V single phase in - 3 phase out drive, see below (about $1000)

AC Drives | Phase Converter VFD | PC1-75 - Driveswarehouse

Then got a 3 phase deep well pump, you would be able to tailor the start up of the well pump so it took several seconds and ramped up to speed. You would also be able to adjust the running speed of the pump, in case you needed more or less water flow.

A setup like this would allow you to run the well on a smaller genset than would otherwise work, since the time response required of the genset would be slower than would be otherwise allowable for starting the well pump with a single phase motor.

I am likely going to be putting in a 550ft well on the property in CO and it is in an off grid location, so the well pump will be by far the largest single electrical load. I will have a greenhouse, but my plan is to put in a large buried water cistern and use a low power well pump that runs for several hours a day to top up the cistern and then for my needs I could use a low pressure high flow booster pump for irrigation (not a high current draw) or a smaller higher pressure pump with an accumulator for domestic water. This means that the submersible pump and its connecting line can be lighter and smaller in diameter so that working on it is not such a bear as what it would be with a more powerful pump with a {necessary) larger diameter line that weighs a ton when you try to pull it out the hole... What is good for the well driller is not always the best for the owner...

 

[TheGoose]

Man, I think you guys are really over-thinking this thing. The breaker protects the wire. You size the wire for the motor according to the charts that are published by several credible organizations. I use Franklin for my information and they have always stood by their data.

Page 11 | AIM Manual | Franklin Electric

For a 5 HP motor on 60degF insulation (common) you need #10 cable and you can run 180 ft from the service entrance to the motor. For 180-280 ft you step up to #8 cable. So hopefully your 5 HP is no longer than 180 ft from the breaker panel to the motor, including the distance to the control box. You have 30 amp breakers, which can handle the starting surge for a fraction of a second without tripping. Once the start event is over, the amps return to normal, about 23-27 amps (the load varies with the quantity of water pumped).

Internally regulated is just a better quality and there is an explanation of it in the Franklin manual. It is more expensive. Externally regulated is cheaper but doesn't react fast enough to maintain the load. It is cheaper. I would buy the generator recommended by the motor manufacturer.

I've done this a few times LOL.

 

[TheGoose]

BTW: Ignore that breaker chart from Franklin. It's the MAXIMUM breaker and not applicable unless you are going with a wire that can handle the surge. What do you think would happen if you put a 60 amp breaker on #10 wire?

 

[dex3361]

Look at the code letter on your starter box. It says code F and a motor code F means you will have between 5 to 5.5 KVA per HP. 5HP x 5KVA is 25KVA which is over 25KW Inrush or momentary KW. Real world it is likely pulling a bit less than full load.

 

[buickanddeere]

BTW: Ignore that breaker chart from Franklin. It's the MAXIMUM breaker and not applicable unless you are going with a wire that can handle the surge. What do you think would happen if you put a 60 amp breaker on #10 wire?

We do that all the time. A 70 amp breaker on a 30 amp wire supplying a 24FLA motor is perfectly legal.
Problem is there are some people who can't tell the difference between short circuit protection and thermal protection. Two different types of electrical protection provided by two different devices.

 

[buickanddeere]

Rather than get too complicated. Just install this factory variable speed drive .

Drives | Residential & Light Commercial | Franklin Electric

 

[EdwardB]

I've got an electrician friend that's going to take a look at this and give me his feedback I bartered him some homemade maple syrup. On that note, the sap is running and we're boiling like crazy. I'll let everyone know what he thinks.