Thermite.

If it goes wrong, the most common fault being the presence of moisture that flashes to steam when the molten copper hits it, it explodes with liquid copper and bits of carbon block as shrapnel. Explosions vary from a petulant 'pop', to people potentially getting seriously hurt 50' away. Cadwelding connections in the rain can be quite a thrilling game. If the Cadwelding doesn't bite you there are fair odds that the torches you use to dry the cables and molds are out to get you.