How should contactor sizing be specified for commercial heating elements?

Size the contactor from the actual current each element group draws, not from its nameplate power: divide rated power by actual voltage, apply roughly a 1.25 safety factor, then derate for frequent switching, enclosure ambient temperature, grouping and duty cycle. Verify the manufacturer's utilization category for inductive or inrush loads and confirm terminal and wiring ratings; undersized contacts overheat, weld and shorten heater life. Also match the coil voltage and control circuit, check that pole count suits grouped switching, and after installation measure per-phase current against calculated values. During acceptance, inspect terminal temperature rise and reliable pull-in, and confirm spacing and ventilation around the contactor.