Ricky Chang :

Going by the system requirements, the choice of 8051 for control seems perfect with no need to change the hardware setup to PLC or anything.

As already pointed out in earlier posts the importance of the following cannot be under estimated :

1. Freewheel diodes across all DC relays / contactors.
2. Snubber circuits across Ac relays / contactors / motor windings.
3. Wiring discipline - control cables laid in the same trays as power cables etc.
4. Adequate power supply decoupling for the MCU 5V dc supply.

Once you have ensured that the above is in place then you can discuss about aluminium enclosures, Faraday cages and similiar stuff.

Raghu