No thermal protection is required because the SmartOne® immersion heater self limits its maximum heat output (below the ignition point of most plastics). Titanium, 316 and 304 stainless steel available - up to 18 kilowatt, single or three phase. Available in three flexible voltage ranges (up to 480 volt). Operates in air, sludge, or scale. Longer lasting and safer than resistive heaters. cULus and CE.