ECN Forum Forums General Topics of the Trade General Discussion Area 20 HP motor

20 HP, 230V, 3PH municipal pool pump-motor with nameplate of 56 amps. It is drawing 64 amps. What could the problem be?

What machine is it driving ?
The machine may have worn bearings or dragging, hence increased motor current.

Take the machine load off the motor and check the unloaded motorcurrent.

Motor armature should run freely with minimal friction.

Pool pumps are usually centrifugal pumps. Centrifugal pumps usually operate in a pretty narrow pressure / flow range, where a slight change in the resistance of the piping will show up as more amps drawn ... though there may not be much change in the discharge pressure.

I'd suggest looking to be sure all the right valves are open; then checing to see if the filter media is in need of replacement / back flushing.

Rod's suggestion - check the bearings and alignment - is also a good idea.

Finally, you said this was a three phase motor. When was the last time your meter was calibrated? Is it s 'true RMS' type meter? Has the increased amp draw been a new development - or has it always been that way? Is the draw the same on all three legs?

I just had a pump that was doing that. I could reduce the current by cutting back on the water flow by closing a valve. I left it as I found it, because it was within the service factor of the motor and it had been running like that for years. I replaced the overload block, instead.

Thank you for the excellent information. Our motor is rather old. It is probably operating within it's service factor rating of 1.15 continuously and we realize that is a problem. We know that it must be replaced soon. (Approx. $4,000.00) Unfortunately my meter is not a true rms. Can someone recommend a nice little clamp on type true rms FLUKE. What is the newest model number available? I really should buy one.

I agree with Renos.
It sounds like the pump isn't running where the system was designed; probably from valves being open/closed in a way that wasn't intended when the system was installed.
If you shut all the output valves the water would have no place to go and the motor would have serious overload issues...that would then obviously not be the motor's fault.
The motor is only responding to what the pump wants in terms of torque and Horsepower.

Frank, I personally do not use Fluke meters. Oh, I have a fancy one ... but I get more utility out of the meters made by Fieldpiece.

Their 'top of the line' is already true RMS, will measure VFD hertz, has a jack for a thermocouple ... all useful in maintenance work. The meter comes with an amp clamp attachment. Total cost is about $200.
There are also numerous accessory heads, for those doing HVAC work.

First post on this site. Looks like a great forum!

High current on water pumps is usually due to how much water you are trying to pump (move). Blockages or valves restricting the suction end of the pump will decrease current, not increase current.
Go to the suction end or valve in that pipe. Temporarilly block the suction with a current clamp on motor lead. The current should drop to about 1/3 of FLA. If there is a valve on the suction side of the pump close it slowly until the desired current is obtained.
Many people have the idea if you block the suction side of a pump or fan the current will rise. The truth is the exact opposite. The pump or fan motor is doing no work unless it is moving water or air.
If the current does not fall way down after blocking the suction end, then I would consider all the suggestions mentioned above.
If this pump has been serviced in the recent past, check the impellar. It may be the wrong one (pitch).

Ditto the above - so long as we are talking about a centrifugal pump. Try running a positive displacement pump with a shut-off discharge or intake and you can do some serious damage.

Fans and centrifugal pumps increase their current draw when asked to do more work - i.e. move more air or water. Move less, and there is less current draw. Big pumps are routinely started with a shut-off head, just to minimize the current draw during startup.

If reducing flow (reducing load) does not reduct current proportionally, then there is a mechanical problem with the pump / motor assembly causing binding or friction. That calls for a rebuild or at least some detailed service work.

Welcome to the board JValdes.

Radar

Welcome to ECN and what a great first post.