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.

 

[Knobhead]

OK the answer to the question asked is YES!
Now that's even less helpful.
If you read the OP, he's not dealing with the motor.
If he wants to prevent a burn out thats a different matter. What would you recomend?

 

[Spoon]

Hi Matthew. As E54 said in post 2, we need more info, like type, size of motor, what it's operation, what enviroment is it working in. (eg dusty) The more info you can give us the more we can help.

 

[clematis432]

OK the answer to the question asked is YES!
Now that's even less helpful.
If you read the OP, he's not dealing with the motor.
If he wants to prevent a burn out thats a different matter. What would you recomend?

If you take time to check, I,ve already "recommended" and with a lot more courtesy than you. Why do you think the OP has not returned ? Maybe due to your attitude/smartness ? I would prefer you not to reply back, I won,t to you, your attitude sucks.

 

[Engineer54]

No-one can give the OP a probable answer to his query, as he didn't give anywhere near the relevant information needed to do so!! He had disappeared even before i asked for further information in post #2 and hasn't bothered to to come back since!!

If there is anyone here that could have given the OP sound directions on his query, it would be TONY. But i know that he won't give out advise to those that disappear and don't come back with information that's been asked for/requested. Far too many OP's do this on the forum, ask a question with hardly any information, get many replies, all based on assumptions, rarely getting any answers and hardly ever get any feedback from these OP's....

On a final note, save but a few here, Tony has probably forgotten more, of what most know here about motors and the control of motors...

 

[clematis432]

No-one can give the OP a probable answer to his query, as he didn't give anywhere near the relevant information needed to do so!! He had disappeared even before i asked for further information in post #2 and hasn't bothered to to come back since!!

If there is anyone here that could have given the OP sound directions on his query, it would be TONY. But i know that he won't give out advise to those that disappear and don't come back with information that's been asked for/requested. Far too many OP's do this on the forum, ask a question with hardly any information, get many replies, all based on assumptions, rarely getting any answers and hardly ever get any feedback from these OP's....

On a final note, save but a few here, Tony has probably forgotten more, of what most know here about motors and the control of motors...

I appreciate Tony has"forgotten more than most of us know about motors and control gear" but hey ! give a new member a break and a bit of encouragement !
There,s a way of answering a post, even if the OP was not very clear. Not difficult really.