How should three-phase connection be specified for industrial heating elements?

For three-phase industrial heating elements, first fix each element's rated voltage and the bank connection. In star, an element sees phase voltage; in delta, line voltage, so actual voltage and total power differ sharply. Never wire by site habit. Have the supplier lock the drawing: connection type, elements per phase, sheath diameter and material, surface load, IP rating, mounting geometry and thermal control. Acceptance should cover cold resistance, insulation resistance, dielectric strength, leakage current and temperature rise, plus phase balance and insulation to earth, with resistance deviation rechecked if needed.