Ohmms reading.

[rpm2]

Q2 please

240v 1500w motor.
a) What reading would you expect on a healthy motor?
b) What reading what you expect on a faulty motor?
and
c) Where would you connect the meter to get the readings?

I know they are daft question to you but the company expect us to find out for ourselves believe it or not.

 

[Marvo]

I'm not understanding your question. What are you trying to measure?

 

[rpm2]

I'm not understanding your question. What are you trying to measure?

The ohmms resistance on healthy and faulty motors.

 

[Lucien Nunes]

Ohms, not Ohmms.

Is this the Saniflo motor? You can't troubleshoot a single-phase motor completely from its terminals, because there's more than one winding inside, and the resistances are low. If it's totally shorted, e.g. 0.2 ohms, there's a problem. Also obviously if it's open circuit. But if I got 10 ohms, I wouldn't know whether it was truly good or not, although I would expect it to do something, either run or blow the fuse, when powered.

 

[rpm2]

Ohms, not Ohmms.

Is this the Saniflo motor? You can't troubleshoot a single-phase motor completely from its terminals, because there's more than one winding inside, and the resistances are low. If it's totally shorted, e.g. 0.2 ohms, there's a problem. Also obviously if it's open circuit. But if I got 10 ohms, I wouldn't know whether it was truly good or not, although I would expect it to do something, either run or blow the fuse, when powered.

Sorry for the typo, yes it is on a sani motor. Thanks for a clear explanation mate.

 

[Lucien Nunes]

One other scenario with a single phase motor is if the start switch or capacitor is faulty, you might get a plausible looking resistance reading at the main input terminals, but the motor just hums instead of starting. Because the current taken by the motor depends on the mechanical load rather than on the winding resistance, you can't calculate from the information on the data plate exactly what the resistance should be (although with experience you can estimate). So you wouldn't know if the starting winding was in circuit or not, and if it's PSC or CS the meter would be isolated from the start winding by the capacitor anyway. So really all you can do, without dissecting the motor and testing the individual windings which you won't be able to do on a submersible, is see whether there's some kind of circuit through it and hence know that it will at least give some more clues when powered.

OTOH you can often spot a winding problem on a small/medium 3-phase motor straight away, because you have three resistances to compare and you can measure them all from the terminals. One open or badly shorted winding and the readings will be suspiciously different.