Selection of Starter

Example

Machine Blower Fan (With highs inertia)
Electric Motors 3 phase 415V 1500 rpm 20PP

Method of Starting

Use Auto- Transformer (for high power or inertia machine)

Initial Starting Current = 1.7 to 4- In (Say 3 In)

Usual Starting Time = 7-12 secs (Say 10 secs)
Rated Current (In) = Set Current (Ie) = 29A

Multiples of current setting Ile on starting = 3 Ie

Selection of Thermal Overload Relay

Try CT31-32• 23-32A Try CT3-45 25-32A
Tripping Time Tripping Time
Cold Start 25 secs (OK) Cold Start 50 secs (OK)
WaLw Start 7 secs (NO) Warm Start 12 secs (OK)