Fluke 289 reading motor Status - Electrician Talk - Professional Electrical Contractors Forum

newton2000 · 09-27-2009, 09:52 AM

Hi if i use Fluke 289 to measure with OHM Status of motor. What reading OHM said if the motor is OK?

mcclary's electrical · 09-27-2009, 10:04 AM

Quote:

Originally Posted by newton2000

Hi if i use Fluke 289 to measure with OHM Status of motor. What reading OHM said if the motor is OK?

There is not enough info to answer your question, And this is not the best tool to troubleshoot this motor. But here it goes, check each incoming lead to ground for a short. If the meter reads open or OL on each, that is good. Any reading phase to ground is not good. Then read phase to phase. Depending on the motor, it could vary anywhere from 5 ohms to who knows what. This is where we need to know your motor sizes. Any "open" or "ol" reading phase to phase means the motor is bad. A continuity reading phase to ground means the motor is bad and you have not given us enough info for a resistance measurement phase to phase

Lone Crapshooter · 09-27-2009, 01:57 PM

The phase to phase value on a 3 phase motor is not important. What is important is that the values are all the same. Working as a industrial electrician I work with motors from 1/4 HP 480V to 2000HP 4160V and I can tell you that from what I have seene is that the larger the motor the lower the the winding resistance. Why is the resistance so low? Because resistance is a DC value 3 phase motors run on AC that brings impedence (opposition to the flow of AC) into the picture. There is also counter electromotive force that is induced back into the stator winding There are a lot of things going on in a motor that limit the current in a motor. That is why that the winding resistance is so low. It is not uncommon for a large motor to have winding resistance of less than 1/2 ohm but runs fine. I checked a 4HP submersible pump the other day it checked 9 ohms P/P.
If you work a lot with large motors you may want to buy a DUCTOR which is a low resistance ohmmeter I use one quite a bit in my work.
Ohmmeters ars useless to check windings to ground. Meggers are the only way to go. If a motor is made up for a voltage it is only necessary to meg 1 lead to ground to ground because the windings are all tied together in the motor . The low resistance of the winding has little effecton the megger test.
LC

wptski · 09-29-2009, 11:40 PM

The Fluke 289 has a special low 50 ohm range setting that uses a higher voltage than the normal resistance range. It's not a megger but it's better suited in this case.

The following from Fluke's site, 289 features:

50 ohm range – useful for measuring and comparing differences in motor winding resistance, low ohm measurements, or other contact resistance. Two terminal 50 ohm range with 1 milliohm resolution, 10 mA source current.