O' Brien Corporation - Electric Heaters

Electric Heater Selection

Electric heat trace products come in a wide range of heater types, accessories and temperature control schemes. There are also a host of safety issues related to electrical code compliance and approvals. Electric heat tracers can be categorized by several factors: output characteristics, the ability to cut-to-length, and temperature limits. Each heater will have its own performance and application limitations.

Output Characteristics: The output of the heater will be either fixed or variable. Fixed output heaters are referred to as ‘constant wattage,’ the output does not vary with temperature. Variable output heaters are referred to as ‘self-limiting,’ ‘self-regulating,’ ‘variable resistance’ or ‘power-limiting.’ In all cases the output varies with the temperature of the heater; as the temperature increases the output decreases. The value and slope of the change varies widely within this family of heater types.

The Ability to Cut-to-Length: This refers to the ability to cut a heater to a desired length in the field without specialized training or tools. If a heater cannot be cut in the field it is referred to as ‘fixed’ length. In order to shorten a fixed length heater it requires specialized training and / or the addition of a transformer or a controller with power limiting capabilities. Cut-to-length heaters are divided into two subgroups: those that can be cut anywhere and those that must be cut at specific locations or nodes. The second subgroup is called zone heaters. The zone length is consistent for a given heater but may vary from one output to another.

Temperature Limits: Each heater will have a maximum maintain temperature as well as a maximum exposure temperature. Exposure temperatures can be rated as power on or power off and a heater may have a higher ‘intermittent’ exposure temperature rating.

Typical Uses	Characteristics
Self Regulating - Low Temperature
Freeze protection for low temperature liquid samples. Can be used without temperature controllers. May be used on semi permanent installations or where moderate flexing and movement is anticipated.	Infinitely Cut-to-Length Maximum Continuous Exposure and Maintain Temperature: 150°F (65°C) Maximum Intermittent Exposure Temperature: 185°F (85°C) Output: 5, 8 or 10 W/Ft * Hazardous Area Approvals: FM, CSA, CENELEC T-Rating: T6 Thermostatic Control: Not Required	J & P Series Tracers
Self Regulating - High Temperature
Temperature maintenance up to 250°F (120°C). Permanent installations with no flexing or movement anticipated.	Infinitely Cut-to-Length Maximum Continuous Exposure and Maintain Temperature: 250°F (120°C) Maximum Intermittent Exposure Temperature: 420°F (215°C) Output: 5, 10, 15 or 20 W/Ft * Hazardous Area Approvals: FM, CSA, CENELEC T-Rating: T3 – T2 depending upon output Thermostatic Control: Required for maintain temp above 150°F (65°C)	B & N Series Tracers
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Temperature maintenance up to 300°F (150°C) with high exposure temperatures. Also used for freeze protection of high temperature lines.	24” Zone Lengths Maximum Continuous Maintain Temperature: 300F (150°C) Maximum Exposure Temperature (Power OFF): 482°F (250°C) Output: 10 & 20 W/Ft Hazardous Area Approvals: FM, CSA, CENELEC Thermostatic Control: Required	JV & JN Series Tracers
Constant Wattage
Temperature maintenance up to 400°F (205°C) in general purpose areas. Often used for stack gas systems. (See caution note about using zone heaters for this application.)	24” Zone Lengths Maximum Continuous Exposure and Maintain Temperature: 400°F (205°C) Maximum Intermittent Exposure Temperature: 400°F (205°C) Output: 18 W/Ft Hazardous Area Approvals: None** Thermostatic Control: Required	T, TN & TY Series Tracers
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Maintain temperatures up to 450°F (260°C). Stack gas systems.	Factory Fixed Length Maximum Maintain Temperature: 450°F (230°C) Maximum Exposure Temperature: 500°F (260°C) Output: up to 30 W/Ft Hazardous Area Approvals: None** Thermostatic Control: Required	Series Resistance Tracers
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Maintain temperatures up to 500°F (260°C) with high exposure temperatures. Stack gas, combined cycle power generation, oil sands extraction.	Factory Fixed Length Maximum Maintain Temperature: 500°F (425°C) Maximum Exposure Temperature: 1100°F (590°C) Output: up to 30 W/Ft Hazardous Area Approvals: FM, CSA, CENELEC T-Rating: determined by application Thermostatic Control: Required	Mineral Insulated Tracers (MI)
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* Nominal output of variable resistance heaters is rated at 50°F (10°C). ** Some resistance and/or zone heater selections may carry hazardous area approvals. Consult factory if hazardous area approval is required. = Re-circulated fluid or steam tracing has its own set of design and installation issues requiring consideration such as pressure, trapping, and system recovery. The discussion of steam and fluid tracing is not covered in this design guide. For more information on steam and fluid tracing visit our website at http://www.obcorp.com.

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Electric Heater Selection