Hi Russell,
You wrote:
Easy solution: Use a PLC (programmable logic controller) as they are cheap and dead easy to program. I fail to understand why someone would bother to lash up a 8051 with relays and write the program in assembler to do such a job. A suitable PLC is less than $100 USD and has a bucket load of protection and is built for industrial control.
Failing this advice, get a PLC and figure out the circuitry so you can built it into your device.
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1. Can you provide a web address of an above PLC?
2. Can you tell how long it would take to learn how to     
   program a PLC?

I think your solution is not going to be "So Easy."
Thank you,
Charles Bannister