setting a dol starter thermal overload

[Welchyboy]

as in the title can anyone help with selecting and setting the limit on a thermal overload relay, the motor is rated at 2.2 KW single phase, is it a case of run the motor at full load, clamp measure the max A then set the overload just above, or set the overload to just below the max CC Capacity of the supply cable?

thanks

 

[somersetsparks]

Well clamping the cable at full load is not a bad idea, For little motors I just look on the plate on the motor and set the overload slightly higher.
The overload is to protect the motor, the fuse/ mcb is for the cable.

 

[johnboy6083]

tong the cable and set to 110% of that.

 

[telectrix]

10-12 A load depending on pf, so overload set 12 - 15A IMO.

 

[Marvo]

If the motor load is fairly constant like a fan unit I measure the run current then add 5% and set the thermal at that.
I would always make sure the overload setting doesn't exceed the max run current on the motor plate. Even at 5% over the max run current you probably won't burn the windings but the excessive heat degrades the bearing lubricant and shortens the life of the motor considerably. This is especially true with the cheaper Far East imports.
Twenty or thirty years ago there was a built-in safety margin and you could run a motor over its specified current with no noticeable consequences......but.....alas.... those days are long gone

 

[mayfair]

Excelent post Marvo

If the motor load is fairly constant like a fan unit I measure the run current then add 5% and set the thermal at that.
I would always make sure the overload setting doesn't exceed the max run current on the motor plate. Even at 5% over the max run current you probably won't burn the windings but the excessive heat degrades the bearing lubricant and shortens the life of the motor considerably. This is especially true with the cheaper Far East imports.
Twenty or thirty years ago there was a built-in safety margin and you could run a motor over its specified current with no noticeable consequences......but.....alas.... those days are long gone