Thermal Overload Relay Setting Calculation

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Thermal overload relay setting calculation.

Over current protection inverse time o c protection calc 51 n directional oc primary secondary current calculation. 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. Max thermal over load relay setting 120 xfull load current phase max thermal over load relay setting 120 x7 9 amp. However if motors are designed with a service factor which is then shown on the nameplate eg.

If o l relay. Hence overload must be chosen closer to the range of 8 6 14 7. Hand reset position in. 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.

2 check your full load ampere using clamp on meter for actual value and compare with your setting. Thermal over load relay line. Thermal over load relay vs ct operated thermal overload relay. For a star delta starter we have the possibility to place the overload protection in two positions in the line or in the windings.

If your compressor always trip 1 use your actual fla value and make calculation and set a new setting for your overload relay. Selection of thermal overload. 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. 1 check your overload relay condition perform test trip to ensure it is function properly if not change it.

Min thermal over load relay setting 70 x7 5 amp. Thermal overload relay setting 70 x full load current phase min. Overload set up when setting up an overload relay to protect a motor in a given situation the following two questions must be considered. 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. Thermal overload relay setting 120 x12 28 14 7a. Thermal overload relay setting 120 x full load current phase max. If the motor is connected in star 440 v 60 hz the overload relay then has to be set to 3 1 a.

Thermal overload relay setting 70 x12 28 8 6a max. Motor protection relay selection curves. 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.