0

The pump is a submersible type around 100ft down. It is rated at 1.5 HP ~ 1.1 KW and is around 3 yes old. The manufacturer's spec sheet mentions a full load current of 9.2 A.

1.1KW/230 gives me a figure of 4.86A, or 6.88A. The utility meter reports a PF 0.92

This is single phase device with the line voltage nominally at 230V 50 HZ. At times it may be as high as 250V.

The meter mounted against the pump shows a **constant ** 11.x 9.7 A after it is powered, which I fail to understand. I can understand a starting surge upto the rated load current but not 200%.

Why is this the case?

2

The 1.5HP rating is the mechanical output power of the motor, not the input electrical power. The way these motors are specified is that they put out rated power at rated current and frequency when consuming the full-load amps. Your naive current calculation fails to take into account motor efficiency and power factor. In other words, the real calculation goes like this:

V * I = P / (eff * PF)

Where V is the operating voltage, I is the current, P is the rated output power, eff is efficiency, and PF is power factor. If you solve that equation for I, that is your expected current. But there is no need to go through the math, because the full load current is already listed on the nameplate as 9.2A. So if everything is working right, and the motor is putting out 1.5 HP, you would expect to see 9.2A.

Still, even though your expectation of 6 or 7A is wrong, it sounds like the motor is consuming more than the full-load current. It is unclear from your post whether this is something new, or if it has been doing this ever since it was installed.

I can think of three reasons you would draw more than rated full-load amps. Reason one is that the pump is running at a higher flow rate and lower pressure than it was designed for. (It may be counter-intuitive, but centrifugal pumps and blowers consume MORE power when there is less back pressure... they consume the least power when the back pressure is highest in the no-flow condition).

The second reason is that something is faulty either in the pump or the motor. Maybe the pump shaft is rotating in the wrong direction or a bearing has worn out.

The third reason is that the voltage is too high and the motor is simply being over-driven.

If you have the make and model of the pump, and know the total vertical head that the pump is working against, we could maybe narrow it down a bit more by comparing your operating pressure against charts in the pump datasheet. It would be good to know if the voltage was 250 at the time you measured the current.

  • At the time the Voltage was 241 – Everyone Apr 26 '18 at 8:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.