ELECTRIC MOTORS ~ WHAT IS "THERMAL?" 1

[manic22]

As far as electric motors, I had a customer call and ask me what "thermal" meant, or what exactly it was. I was wondering if any of you could help me. Descriptive answers would be much appreciated!
Thanks a lot,
Kimberly

 

[jraef]

Temperature.

"Venditori de oleum-vipera non vigere excordis populi"

 

[buzzp]

Thermal means how much heat the motor can handle. This is often associated with starts/stops the motor is designed for, the ambient temp, the running amps, etc.
The thermal capacity of the motor is often simulated with protective relays to know how long the motor can run, based on starts/stops and running amps. For example, it starts twice an hour and is running slightly above nameplate amps. After two hours, the motor may only be allowed to start once an hour because it is at its thermal limit. Thats a crude example but hope it helps.

 

[peebee]

Depending on context, "thermal" might have been used to refer specifically to the "thermal overload" protective device (or relay) required to be located in either the motor or the motor starter. Usually, most people would call that device an "overload" for short, but you might hear someone call it a "thermal".

I agree with the other posts above too.

 

[Marke]

Quite often, small single phase motors include an internal bimetal assembly (or thermal) as an overload detection device. This can come under a variety of different name and descriptions, but the purpose is to shut the motor down if it is overloaded.
Best regards,

Mark Empson

http://www.lmphotonics.com

 

[light1]

"Thermal" is used in various contexts when it comes to electrical motors. Several contexts have already been mentioned in the above postings.
The following appear to be due:
1. The Thermo- or Thermal-magnetic circuit breaker in contrast with the Magnetic circuit breaker often used for motor protection in MCC compartments housing motor starters. Thermal-magnetic circuit breaker often protects the motor starter where the distances between this breaker and starter is longer; therefore, the protection of cable/conductor run is justified by this breaker. Magnetic breaker does not protect conductors against overloads.
2. Motor thermal damage curve is plotted in I-t plane with other protective devices characteristics that are supposed to be properly coordinated with this curve.
3. Thermal or temperature insulation rating that can be B, F, H, etc. for example. This rating essentially sets the maximum motor winding temperature not producing the insulation damage and premature aging of the motor.