Interfacing AC power lines

[Archangel]

Hi,

Thanks for your replies.

The application is controlling a 3 phase welder with current feedback giving between 200 & 3000 amps. I already have a working product, but on some sites the welders act strangely. I eventually thought what are the 3 phase inputs refferenced to? So I am now thinking i need to connect the pcb's 0V line to Neutral or earth. Earth would be best since most 3ph supplies dont have a neutral connected in practice.

Bob...

Hi Bob,
Your welder is producing up to 130000 watts of plasma arc (assuming a peak of 46 volts, just a guess) anyway that's a whole lot of RF floating around. You should shield your PIC in a metal box grounded to the welder. I assume you are using 4 wire 3 phase with the fourth wire being ground. Mister_E's recommendation of an opto coupler is a good idea, also shield the wires going into the box containing the pic. I had friend who raced a Midget car with a radio and it would cut the ignition when he keyed the mic due to R/F, shielding fixed it.
JS