Current measurement before and after Contactor

[MayankBhatia]

Hi guys..i have came across a different Behaviour of Current measurement device im working on Single Screw Compressor Chiller.With starting method of soft starter so in that 3 Phase wire goes direct to 3 terinal and to co plete the circuit other goes via SCR and Contactor.

NOw the problem im facing is when i measurement current before contactor im getting as normal at full load 130A but when i take after contactor its showing only 70A this is only of a single phase current.


So anybody could help

[Frikkie]

Your ammeter is designed to measure current which is asine wave at 50Hz, it will accurately measure the current on the supply side of the soft starter. On the load side (compressor or motor side) of the SCR the frequency of the supply may no longer be 50 Hz and SCR's don't give a sine wave output so you will get false readings from a standard ammeter.