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## LEARNING TASK 1 The OLR has two basic parts: - A heater element, which is connected in series with the line to the motor - A normally closed, auxiliary contact, which is connected in series with the coil of the magnetic contactor The CEC requires that each line of a three-phase motor have OLR p...

## LEARNING TASK 1 The OLR has two basic parts: - A heater element, which is connected in series with the line to the motor - A normally closed, auxiliary contact, which is connected in series with the coil of the magnetic contactor The CEC requires that each line of a three-phase motor have OLR protection by: - Using three single-pole OLRs, each with a heater and an auxiliary contact, or - Using a single three-pole OLR, in which a single auxiliary contact is activated by any of three heaters ### **Figure 3 - A three-phase motor starter** | | | | |---|---|---| | Line connections | | | | Stationary contacts | | | | Movable contacts | | | | Thermal unit OLR | | | | Motor connections | | | | | $L_1$ | | | | | $L_2$ | | | | | | | | $L_3$ | | | | | | | $T_1$ | | | | | $T_2$ | | | | | | | | $T_3$ | | | | | | | | $M$ | ## Heater selection Manufacturers of motor starters usually provide a heater table on the inside of the enclosure door. Be careful to select a heater that corresponds with the nameplate current rating of the motor. ## Tripping and resetting Depending on the manufactured design, a tripped OLR is identified by a protruding plunger, a flag or a coloured disk. If the motor starter has tripped because of overload, you must do the following: 1. Determine the cause of the overload 2. Wait for the OLR to cool down 3. Reset the OLR ## CONSTRUCTION ELECTRICIAN APPRENTICESHIP PROGRAM: LEVEL 1