#  > Faadoo Engineers Zone - For Students in Engineering Colleges >  > Engineers Discussion Zone - Ask and resolve queries and so much more.. >  >  Difference between High Impedance Relay Vs Low Impedance Relay

## rinkalrr

Que.
What is difference between High Impedance Relay Vs Low Impedance Relay?





  Similar Threads: E book on numerical /Digital relay AutoReclosure Relay Protective Relay book. Explanation of the  IMPEDANCE RELAY block diagram Relay coordination seminar report/pdf download

----------


## surajp

Low impedance relays are used to switch high currents(like motors) while high impedance relays are used to switch low currents

The reasoning is as follows.

Relays used to switch higher currents need thicker contacts (to minimise heat and power loss), so the thicker the contacts are the heavier they become. Now to attract the contact (to achieve switching operation) the magnetic attraction has to be more powerful (because of the additional weight), implying the relay's coil should generate a higher magnetic flux. To have a greater magnetic flux, the current through the coil should obviously be higher. To facilitate higher current in the coil the resistance (impedance) of the coil should be lower. 

Low impedance relays are bigger and more expensive, so try to use higher impedance relays wherever possible.

----------

