required solution for RTC data corruption and microcontroller reset

Dear sir
We have designed a circuit for

switching ON and OFF electrical

loads (of capacity 3KVA to 100

KVA) using electrical contactors

and also controlling/varying the

input voltage to the load using

multiple tapped auto transformer.
The contactor and the tap

changing is controlled based on

inputs from real time clock
and control program in the

microcontroller Atmel 89c51.
We are observing that the time in

the real time clock is getting

corrupted and microcontroller

program is reset after the

changed time.This usually occurs

when the electrical loads are

switched On or OFF.

Please suggest us the reason.We

have tried to take care of EMI by

enclosing the PCB in a metal box.

Regards

Vishnu

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