Electric Motor Starters

What do you mean by u/v coil?

Context? Six words is not enough.

Is it under voltage & shunt trip Coil used in breakers?

The under voltage coil, protects the motor to start when the supply voltage is to low. Per example in case you want to start a 400 Volt motor on 110 Volts supply.

The currrent sensor gives a signal when the motorcurrent is to high, per example in the case of an overload.

I hope this helps....

If you mean u/v coil as in thermal overloads on motor protection overload relays, which is made of bimetal strips, consisting of under voltage strip and over voltage strip...then these strips break or trip due to under voltages and over voltages as shorts or motor over loading to protect the motor.

Where as the holding coil refers to contactors which consist of coils which are ennergized by some control voltage (240Vac,110Vac) to give rise in the magnetic flux which creats a north and south pole on the contactor cores (top and bottom) which pulls (unlike poles attrack) in making top and bottom contactor contact switches met, engaging 3 phase power to the motor windings. As long as the coil is energized it holds in contactor switches, until it is de-energized where the control supply is not present, for the magetic field is lost, breaking the contactor switches.