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Discussion Starter · #1 ·
We have a downhole pump that the record drawings, and old contract specs list as 3/4-horse. Calculating the water horsepower indicates 0.69-horsepower. So, that is probably correct.

The flow dropped this year at start up. (It is on a Forest Service residential compound that gets closed for the winter every year.) As part of troubleshooting the system I checked the power draw. I used a Fluke fork meter and got 9.7-Amps at 248-Volts, and using a clamp meter [email protected] Which works out to a bit over three horsepower.

This seems really excessive, unless the pump is completely wrong for the application and running way off the side of the curve.

Anyone have an explanation?
 

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We have a downhole pump that the record drawings, and old contract specs list as 3/4-horse. Calculating the water horsepower indicates 0.69-horsepower. So, that is probably correct.

The flow dropped this year at start up. (It is on a Forest Service residential compound that gets closed for the winter every year.) As part of troubleshooting the system I checked the power draw. I used a Fluke fork meter and got 9.7-Amps at 248-Volts, and using a clamp meter [email protected] Which works out to a bit over three horsepower.

This seems really excessive, unless the pump is completely wrong for the application and running way off the side of the curve.

Anyone have an explanation?
Are you sure it's only 0.69-horsepower?

Is it possible that someone changed the pump to a larger one?
 

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Is this a well pump? Not sure what a down hole pump is. Looking around online at 3/4 hp well pumps they run in the 8a range fwiw
 

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Water horsepower ?
As Davis said , if it's well pump normal range.
If you don't maintain head pressure on the pump the amps will be higher and shorten the life of the pump head as well , leading to less water being pumped/ volume.
 

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That's high, but not as high as it sounds. There are too many losses in a motor for a straight horsepower-to-amps conversion, the actual FLA is going to be much more than that. Looking at Table 430.248 and it lists your FLA close 7 amps which is probably more realistic.

That said, if your flow is down, but your current is up, is there a chance in the world you've got a busted impeller? I don't know much about down-hole pumps, but I know on centrifugal impellers, reducing the restriction can drastically overburden the pump.

Also, where are your OLs set?
 

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According to the Franklin pump motor book, if it's 2 wire, the full-load current should be 6.8 and the maximum permitted is 8.0 Locked rotor current is 34.2

If it's 3 wire, the current on yellow should be 4.9 with 5.7 max, 5.0/5.2 on black and 3.1/3.2 on red. Locked rotor current is 34.2

248 volts is pretty high, that will cause high current, but not as high as you are reading.

The reason the calculated HP differs from the actual HP is power factor. The PF for the 2 wire motor is 62%, the 3 wire one is 84%. This is normal for a motor of this type.

Were the readings taken at normal pressure? Every centrifugal pump will draw more current at lower pressure.

Does the water have minerals and stuff in it? If so, very likely the bearings are dragging because of mineral buildup.

Typically, submersible pump motors are run at least full-load, and more often than not, into the service factor. The expected current will be at least full-load, often higher, but never higher than the maximum.
 

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Just to clarify if you don't keep head pressure on the pump the impellers will float up and apply pressure against the diffusers causing much more friction and wear .
I saw the results first hand when customer was using pump to fill pond and against the advice of others run it full open and spoiled the pump in no time.
As far as overloads go in fractional horsepower it depend on type most 2 wire systems overloads are built into motor.
On 3 wire systems usually built into starter box.
Does the pump seem to run excessively ?
Could be a hole in line somewhere .
I've saw the adapters rot leaving a nice size hole in the well for water to escape
 

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Discussion Starter · #8 ·
The water horsepower of 0.69 on a 3/4-horsepower pump indicates the hydraulics of the pump are ok.

It pumps against 70 to 78-psi, other than about five to ten minutes at start up. When it starts against the empty system until it fills to the hump in the system. It then pushes against the 70-psi until lit gets the system in the compound filled and then it fills the 2000-gal reservoir and cuts out at about 78-psi.

I'm surprised at the size of the pump. I'd have sized it at about 2-hp to meet the demand in a shorter time period.

I was concerned with the amp draw, as it seems high to me relative to the horse power rating of the pump.
 

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You may not have a well capable of pumping faster than that. Hard to say how many gallons per min the well could supply.
As you said though once the system is full it probably doesn't need all that volume under normal use.
Cheaper to run on a daily basis than a bigger pump.
 
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