1. System voltage (e.g. 120V, 220V, etc)
2. Gauge of power cord (e.g. 8 AWG. The datasheet for NUWU cord is at the following link. Scroll down to the 2nd page to see the first column labeled "Wire Size". Then look on the power cord to find a number that matches, and post it.)
www.nexans.ca/eservice/.../NMWU_SUPERVE...
3. Motor nameplate data: Volts, Amps (or no amps shown, Watts), and phases (1 or 3).
It sounds as though you have a special power supply. If it is an inverter that puts out a modified square wave, that *might* cause a problem.
If the voltage you read is at the power supply and not at the end of the cord while the motor is running, that value, although useful, isn't the critical number to know. However, you can provide the above information in lieu of measuring the voltage at the motor if you like.
EDIT 2013-08-21:
Thank you for the additional information. It undoubtedly is a single-phase load due to its small size and the fact that no one uses 120V three-phase power systems.
The manufacturer's specifications (page 26 of 106) indicate the unit will tolerate an input voltage of +/-10%:
http://www.vacuubrand.com/context/manual...
Since the nameplate states 115V at 60Hz (the 110V applies to 50Hz), that means the voltage at the unit should be in the range of 103.5V - 128.5V. I calculated the voltage loss in the power cord, assuming 120V is applied at the source end, and using the following parameters:
length = 75m = 246ft
load = 5.7A at 80% power factor
wire: copper, 10AWG, not in magnetic conduit
That results in a voltage drop of about 2.9V, or 2.4%, which is well within the range in which the unit will operate. (Note that online calculators usually assume a 100% power factor, which results in a larger drop of 3.5V 2.9%, but equipment with motors have a lower power factor, especially single-phase fractional horsepower motors.) The conclusion is that your power cable size is quite adequate (unless you have additional loads connected).
That brings us back to your power source as being the possible culprit. Can you move the equipment temporarily and plug it directly into the backup power supply? Can you bypass the backup power supply?
Frequency is, without a doubt, _not_ the issue.
Are you checking the voltage under load?
It's not enough to simply connect a voltmeter to the end of the extension cord. The pump must also be running when you make the measurement.
Also, keep in mind that the current draw when a motor starts up is particularly large, so your voltage drop will be worse. If the motor never really gets up to speed, it may never even switch out the starter capacitor (which is accomplished with a centrifugal switch).
What is the current rating of your motor and what is the gauge and length of your extension?
No, it's not the frequency, but the current can be.
Very long extension cords should be heavy gauge if you intend to run something drawing a high current through it, such as power tools or motors. If you run the pump through too long of a low-gauge cord, the result will be poor delivery of power, overheating of the cord, and even a fire. Stop using the pump/cord combo immediately. I know heavy extension cords are expensive, but you don't want to burn your house down.
Frequency CANNOT change, so forget that, the problem is somewhere else. Perhaps in your monitoring equipment.
Did you check the voltage at the pump? Long extensions are not good for motors. What is the rating of the motor, and what is the size and length of the extension.
It is not the frequency that is dropping, it is the voltage at the pump. Check the pump current required and choose an appropriate (probably larger) wire diameter for your cord.
Frequency does not change, but voltage does. Check it.
NO, AND NEVER !!!
I have no idea if that is even possible, but I'm having some issues running a pump a the end of a fairly long extension cord. Apparently the performance can be affected if the frequency drops below 60Hz.
