ZCT and Nuissance Tripping for EFR Problem

You said the ZCT is surrounding the busbars. You may like to verify: Whether the ZCT is of appropriate shape for the rectangular shaped busbars (circular shaped CT is not suitable). Refer vendor manual for the details.

Thanks for PWSlack and Wal for comments. We have done Megger test on the cable and switchboard. From testing report no problem (insulation value was still as standard). Downstream of main switchboard is connected to motor control ceter(MCC) which have 3200A rating also and have EFR connection also (MCC for this chiller loads). If we started 1st chiller, no tripping EFR on main switchboard and EFR on MCC incoming. But when 2nd chiller started EFR on mainswitchboard tripped and no tripping on EFR MCC (MCC supplied from mainswitcboard). As PwSlack said, I'm not sure that earth fault exist in the system because 1st chiller motor could be run, but this problem appear when 2nd chiller starting. An alternative, I released the EFR connection(by pass or protection only depend on ACB) on main switchboard feeder, but EFR on MCC was still in line. After doing that, no trip again and system could be running well. So thats why I thought there was problem with 2nd motor chiller starting (false trip). But I still mitigate it. Total capacity of 2 chiller's run is around 1000A. At that time I saw the ZCT (toroid) rating capacity is differrent with ACB rating. If this CT is CT per phase, I know its dangerous (because total load on MCC will around 3000A because any other load). But, this type is ZCT (zerro current CT) that in my mind, this ZCT only sense residual or zerro sequence current where not so big (will not reach big value). For information, our Vigirex fault rating up to 30A only with time delay max. 4.5 second.

That's all very interesting, however, as long as the unit is still tripping, the earth fault remains regardless of any personal uncertainty. So tell the Electrician to go back, find it and eliminate it; the first thing to check is the second chiller. Do it this morning/now/within the hour - it is urgent on safety grounds.