The relay trips the starter when there is an overload. The starter can be restarted as soon as supply is back to normal. A procedure similar to the one described for setting relays in DOL starters can be followed for Star-Delta starters.Ģ) Tripping of starters A starter may trip due to the following conditions a) Low voltage or failure of power supply b) Persistent overload on the motor In the first instance, the tripping occurs through the coil which opens the contacts when voltage falls below a certain level.
It should, therefore, be set at 0.6 times actual load current. The relay should never be set at more than the actual current drawn by the motor (The actual current drawn by a motor will be less than the full load current in most of the cases, as motors may not be loaded to capacity.) The relay operates on the phase currents in Star-Delta starters. If it trips, increase the setting to 85% or more. Here is a simple procedure for setting the relay to the actual load current: Set the relay to about 80% of full load current. This value should be equal to or lower than the full load current indicated on the motor name plate. For all direct-on-line starters, relays should be set to the actual load current of the motor. A selection table indicating the proper range for different ratings is given in section VI. Selection of a relay for a starter depends upon motor hp and duty. 1) Relay setting The overload relay unit is the protection center of the motor starter.
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