Star/Delta, but not as I know it.

[Tayters]

Hoping someone could shed some light here please.
This is a copy of a Carrier water chiller condenser fan schematic. The motor is a star/delta which I understand.
Well I thought I did...

On this one the delta part is as normal. Note how L3 however is switched through the delta contactor KM12.
When in star this means no feed to W1 of the motor from this phase. Instead it comes from L1, through the main contactor KM11, through the star contactor KM11A and through capacitor C11.
In simple terms it's using 2 phases and the third phase is one of the others through a capacitor.

Why?

I suppose that has the effect of shifting the phase round a bit like in single phase motors. My guess is so it starts with less current? Or would it take more and there is some other reason - I've seen much bigger motors with bigger fans wired up as normal so that theory not quite sound anyway.



Carrier Condenser Fan Motors.jpg

Many thanks,

Andy.