Cold Weather Catalog - Chromalox Precision Heat and Control

TechnicalHeat Tracing ProductsApplication & SelectionGuidelines (cont’d.)Step 3 — Select HeatingCable Wattage RatingAfter calculating the heat lossin the pipe and adjusting for anyapplication deviations, you maydetermine which cable ratingto use. If you have selected aself-regulating cable you mustadjust the output based onmaintenance temperatures,using the Thermal OutputRating Graphs shown on the individualproduct pages, selectthe lowest cable rating that willprovide the pipe maintenance temperature.For Example: A15 W/Ft. SRM/E cable @ 150°Fwill output approximately10 W/Ft. Multiple passes or runsof cable may be required toprovide suffi cient output perfoot calculated in Step 1. This isaccomplished with parallel runsof cable or spiraling. Contactyour Local Chromalox Sales offi ce.Cable Output vs. TemperatureHeat Output (W/Ft.)2420161284030 50 70 90 110 130 150 170 190 210 230 250 270 290 300(°F)TECHNICALStep 4 — Determine Total Length ofCable RequiredStep 5 — Determine Circuits &Circuit ProtectionThe total amount of heating cable isdetermined by adding the total footage ofpipe to be traced and adding for allowancesfor the components such as fl anges, valves,pipe supports; then, multiply by the totalnumber of runs or Wrap Factor determined inStep 3.(Total Feet of Traced Pipe + Cable Allowancefor Components) x # of Runs = Total CableLength)Pipe Component Cable Allowance EstimationCircuit protection depends on the breakersize being used and the start-up temperature.The National Electric Code (NEC 1996)requires the use of ground fault protectionbreakers for heating cable. Refer to thespecifi c data of the individual heat trace cableto determine maximum circuit lengths. Todetermine the number of circuits required foreach pipe, divide the total cable length foundin Step 4 by the maximum circuit length foundin the individual cable data charts. Round upto the next higher number.Number of Circuits =Cable LengthMaximum Circuit LengthComponent Cable Allowance Factor (Ft.) x # Components Total Additional CableFlange Pair 1.5 xPipe Support 2.0 xButterfl y Valve 2.5 xBall Valve 2.7 xGlobe Valve 4.0 xGate Valve 5.0 xExample: Pipe: 150 feetValves:1 globe valvePipe Supports: 2Flanges: 2Total Cable Length = [150 + (1 x 4) + (2 x 2) + (2 x 1.5)] x 2 runs= 161 feet x 2 runs= 322 feet197