i work in a fab shop and to alot of tig welding, you use DC for most metals and AC for aluminium and a few other non-ferrous metals. typically in DC mode it will use a high frequency to start the arc easier and in AC it uses a continuous high frequency, which you can set the Hz and balance of to improve the quality and cleaning of the weld. i have never heard of grounding the output of the welder but we have never had problems with our phones, 2way radios, or nextel when welding, i will ask our welding equipment company on monday if they have ever heard of this. hope it helps
rob
