overheating motors

[MatthewC]

Can a motor overheat and short to earth if it is having to work to hard?There is no overload but the motor is protected by thermistors and a thermistor relay which cuts out on occasions. Its an intermittent fault but the Engineers that have watched the circuit say it trips the Main C/B. On a quick inspection today each winding to earth was >200Mohm so no fault there.

 

[Engineer54]

It would be nice to be furbished with a lot more information on the type and size of motor and what it's operation, pump motor, fan motor, etc,etc!!!

 

[telectrix]

vibrator motor???

 

[Martyc]

vibrator motor???

After continued use the dampness causes a short?

 

[ayjay]

not dampness martyc- moistness

 

[Knobhead]

If you know the motor is overloaded why don't you sort that out. As for running without O/L's. You deserve to have a burnt out motor!

 

[Silly Sausage]

I reckon it's upside down.

 

[Knobhead]

˙sʇnɐɟ ɹoʇoɯ ʇnoqɐ ǝlɔıʇɹɐ pooƃ ɐ s,ǝɹǝɥʇ ǝɹǝɥʍ ʍouʞ I

 

[clematis432]

If a motor "shorts to earth" it normally stays "shorted to earth" and if the earth is in the windings, said motor will have to be replaced. The motor should not overheat if thermistor protection is set properly. Some special purpose motors, DO NOT have overload protection and are mainly protected by thermistors and fuses, although this is rare. As Tony said, if the motor is being overworked, the motor could be undersized. I would also check if the windings are balanced (each phase is taking the same current) I am assuming, although you don,t say, that it is a 3-phase motor. If not, cancel all my longwinded opinion !! Without further info, I would go for mechanical/process induced overloading and not an electrical issue. Intermittent problems ! Sent to try us !

 

[Darkwood]

Could be a few things but at a guess the motor is stalling for some reason this will ramp the current up high and probably take a small duration to trip the mcb but because of the time needed to trip the mcb its allowing the thermal cutout to operate....Motor overload protection is for this very senerio try fitting one to circuit.....
Well thats my stab in the dark ....if the mcb tripped on short it would be unlikely to take the thermal cutout with it.

 

[Knobhead]

Could be a few things but at a guess the motor is stalling for some reason this will ramp the current up high and probably take a small duration to trip the mcb but because of the time needed to trip the mcb its allowing the thermal cutout to operate....Motor overload protection is for this very senerio try fitting one to circuit.....
Well thats my stab in the dark ....if the mcb tripped on short it would be unlikely to take the thermal cutout with it.

If anyone expects a MCB to protect a motor against overload they are sadly mistaken.

 

[mechelec]

You could have a short within a winding which would not show up with an insulation resistance test. You may see it with an ohmmeter but more likely need an inductance meter.

 

[Darkwood]

If anyone expects a MCB to protect a motor against overload they are sadly mistaken.

Seen it myself a few times, its when the average house basher looks up on tintinet how to wire a motor .... its works job done attitude ...Whats overload protection dosn't the mcb do that?? Oh wait yes it does ...... if only it was that easy ....one efficient electromagnetic heater at the first sign of a stall, when i retire it be the one smell i'll miss, open terminal block a quick smell and if its real strong tell customer motors buggered without unpacking the test leads.

 

[Darkwood]

When you say it trips the main CB is it a mccb panel main switch with external trip monitor ....ie you can loop the E-stop etc to it to cut main power to panel, this would change the view of the issue as a damaged impellor or a blocked filter etc would all lead to the motor tripping the thermal

 

[clematis432]

If you know the motor is overloaded why don't you sort that out. As for running without O/L's. You deserve to have a burnt out motor!

The OP is asking a pertinent question and looking for advice from the forum. All your doing is being a smart --- with your reply, no help or advice from you eh! Maybe that,s why the OP is not replying with more info,etc.