How does a dol starter work?

A Direct-On-Line (DOL) starter is an electronic 3-phase motor-control system which offers soft starts in DELTA configuration. DOL starters are now replacing the use of manual or semi-automatic "star-delta" starters.

In this way of starting a 3-phase motor, full line voltages are applied to the motor through relays and contactors. The DOL is nowadays the most common type of 3-phase motor starter used.

It has a "closing circuit" and an "opening circuit". The closing circuit is for applying the service lines to the motor and the opening - or "tripping" - circuit protects the motor by cutting-off (or "tripping") power to the motor from the service lines if there is any overload condition, a single phasing fault, etc.

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