Max. Temp of ET in C1D2 area

[CYBER.MIC]

Electric heat Tracing(ET) in Class 1 Division 2 area is required temperature less than the lowest Auto-Ignition Temperature(AIT) in this area,
but more than 80 percent of the AIT.

Does NEC code allow to use ET more than 80% of AIT (but less than AIT) in C1D2 area?

Thanks.

 

[don_resqcapt19]

The code rule is not clear, but it appears that as long as the heat trace is listed for Class I, Division 2 locations you can use it without reguard to its operating temperature.

(B) Class I, Division 2 In Class I, Division 2 locations, all utilization equipment shall comply with 501.135(B)(1) through (B)(3).
(1) Heaters Electrically heated utilization equipment shall conform with either item (1) or (2):
(1) The heater shall not exceed 80 percent of the ignition temperature in degrees Celsius of the gas or vapor involved on any surface that is exposed to the gas or vapor when continuously energized at the maximum rated ambient temperature. If a temperature controller is not provided, these conditions shall apply when the heater is operated at 120 percent of rated voltage.
Exception No. 1: For motor-mounted anticondensation space heaters, see 501.125.
Exception No. 2: Where a current-limiting device is applied to the circuit serving the heater to limit the current in the heater to a value less than that required to raise the heater surface temperature to 80 percent of the ignition temperature.
(2) The heater shall be identified for Class I, Division 1 locations.
Exception: Electrical resistance heat tracing identified for Class I, Division 2 locations.

 

[markstg]

Check out IEEE 515, Standard for the Testing, Design, Installation, and
Maintenance of Electrical Resistance Heat Tracing for Industrial Applications.

 

[weressl]

Electric heat Tracing(ET) in Class 1 Division 2 area is required temperature less than the lowest Auto-Ignition Temperature(AIT) in this area,
but more than 80 percent of the AIT.

Does NEC code allow to use ET more than 80% of AIT (but less than AIT) in C1D2 area?

Thanks.

Since electric tracing application for hazardous area has to be designed on an individual basis, therefore the maximum exposed temperature is calculated taking into consideration insulation K factor, thickness, maximum process material temperature, etc. The design also takes into consdieration overvoltage and thermostat failure runaway conditions. All these will likely result in that your tracer, under normal operating conditions, will have a surface temperature that is below the 80% of the AIT given to the HT Manufacturer/Design Service.