You can measure electrical power at the motor (current and voltage), but you would need to convert to mechanical shaft HP at pump. You need to do a little more research for this. You have to account for motor efficiency:
https://www.engineeringtoolbox.com/electrical-moto...

For large and critical pumps, then consider a direct measurement of pump shaft torque and speed to get shaft HP. Check out Binsfeld wireless torque system. I have an older model.

Walt

What's the purpose of taking the measurement, i.e. what are you trying to determine?

This is for maintenance purposes. Measuring the current against the pump faceplate to determine latent faults. Not sure on the method.

Measuring power input doesn't really tell you much about the pump performance other than it's drawing more or less current - it's of use if used in conjunction with flow / head measurements.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

recently i faced ampere issues on condenser pump, the full load amps was 90A, but draws only 40A. the site contractor even overhauled the pump, checked impeller size...etc. but the actual problem was the discharge butterfly valve was stuck....

Thanks for your feedback. I think the question I should've asked, is where you measure the Full load running current on a pump.

At the motor terminals,or are we missing something?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

Usually easier and safer at the MCC where there's more slack on the conductors to clip a current probe or tong-tester around one of the cores.

The 'full load amperage' is the load that would be on the motor if it was loaded to its full nameplate rating.

It really has nothing to do with how the pump is operating, I do not know of a single pump that is configured to run at the FLA of the motor.