Thermal Overload Relay Setting Calculation

Hi friends in this article i am talking about thermal overload relay working principle and its function in a dol starter.

Thermal overload relay setting calculation.

1 15 the set current for the overload relay can be raised by 15 compared to full load current or to the service factor amps sfa which is normally indicated on the nameplate. Thermal over load relay line. If your compressor always trip 1 use your actual fla value and make calculation and set a new setting for your overload relay. Thermal overload relay is simple over current protection it does not protect from single phasing or phase failure short circuit and earth fault the operating principle of the relay is when current flow through a conductor increases then i 2 x r loss also increases heat loss or ohmic loss.

Hence overload must be chosen closer to the range of 8 6 14 7. Thermal overload relay setting 70 x full load current phase min. Min thermal over load relay setting 70 x7 5 amp. Thermal element 49 provides starting and overload protection based on motor nameplate rating separate model for rotor and stator takes into account negative sequence heating effect short circuit protection guideline instantaneous phase set at 2 times ilr set at 1 2 times ilr 10 15 cycle delay ground.

Thermal overload relay setting 70 x12 28 8 6a max. Max thermal over load relay setting 120 xfull load current phase max thermal over load relay setting 120 x7 9 amp. Sizing for overload is important to avoid serious damage for electrical application such as motor starter machinery or others electrical equipment. A thermal overload relay works on the heat produced by the excessive overload current the heat produced by the overload current is utilized to trip the motor circuit.

Over current protection inverse time o c protection calc 51 n directional oc primary secondary current calculation. For a star delta starter we have the possibility to place the overload protection in two positions in the line or in the windings. Hand reset position in. Thermal overload relay setting 120 x12 28 14 7a.

However if motors are designed with a service factor which is then shown on the nameplate eg. Thermal over load relay vs ct operated thermal overload relay. If o l relay. 2 check your full load ampere using clamp on meter for actual value and compare with your setting.

Should the overload relay be set to the hand reset or auto reset position. According to nec the general requirement for overload sizing be set around 115 or 125 from full load ampere we should setting the overload relay within this parameter to avoid electric motor from serious damage. Thermal overload relay setting 120 x full load current phase max. I hope you will find this article informative and helpful.

If the motor is connected in star 440 v 60 hz the overload relay then has to be set to 3 1 a. Calculation of idmt over current relay settings 50 51 50n 51n calculation model for thermal relay siemens 7sj64. What load current value should the overload relay be set at. Motor protection relay selection curves.