Electric Heat TracingMaintenance and Troubleshooting Guide

1

Introduction

A complete electric heat tracing system willtypically include the following components:

1. Electric heattracing cable1

(self-regulating,power-limiting,parallel constantwatt or seriesresistance).

2. Powerconnectionkit.

3. Control thermostat2.

4. In-line/T-splice kit(permits two or threecables to be spliced together).

5. Cable end termination.

6. Attachment tape (use on 12"intervals or as required by codeor specification).

7. “Electric Heat Tracing”label (peel-and-stick labelattaches to insulationvapor barrier on 10'intervals or as requiredby code or specification).

8. Thermal insulation3 andvapor barrier (by others).

The absence of any of these items cancause a system to malfunction or represent asafety hazard.

Notes . . .

1. Ground-fault maintenance equipment protection is required for allheat tracing circuits.

2. Thermostatic control is recommended for all freeze protection andtemperature maintenance heat tracing applications.

3. All heat-traced lines must be thermally insulated.

Cable Testing

After a heat tracing circuit has been installed andfabricated and before the thermal insulation isinstalled, the heating cable should be tested toensure electrical resistance integrity. The cableshould be tested with at least a 500 Vdc megohm-meter (megger) between the heating cable buswires and the heating cable metallic braid. It isrecommended that the test voltage for polymer-insulated heating cables be 2500 Vdc or 1000 Vdcfor MI cable.

After properly terminating the cable, connect thepositive lead of the megger to the bus wires andthe negative lead to the metallic braid as shown.The minimum acceptable level for the meggerreading for any polymer-insulated heat tracingcable is 20 megohms. This test should be re-peated after the thermal insulation and weatherbarrier have been installed.

Connect the positive lead of the megger to the cablebus wires and the negative lead to the metallic braid.

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Final Inspection

The heating circuit can now be tested for properoperation. This includes measuring and recordingthe connected voltage, steady-state current draw,length and type of cable, ambient temperature andtemperature of the pipe. (See the InspectionReport Form on page 3.)

The complete system (especially the thermalinsulation) should now be visually inspected.Additional insulation should be applied snuglyaround pipe shoes or other heat sinks and sealedfrom the weather. Expansion joints on high-temperature lines should be examined carefully.There may be exposed insulation where sections fittogether or around flanges, valves, pipe hangers orconnection kits; these locations should be sealedto prevent ingress of moisture.

“Electric Heat Tracing” caution labels should beapplied to the outer surface of the weather barrierat regular intervals of 10 feet (or as required bycode or specification). The location of splices andend terminations should also be marked with spliceand end termination caution labels.

Maintenance

Once the heat tracing system has been installed,an ongoing preventive maintenance programshould be implemented using qualified personnel.Support documentation providing general informa-tion and an operating history of the specific cir-cuits in the system should be maintained.

The results of the operational testing describedabove form the testing “base line” or normal range.Subsequent measurements should be recordedperiodically and compared to this base-line data tohelp identify potential malfunctions.

Thermal Insulation

The value of properly installed and well-maintainedthermal insulation cannot be overemphasized.Without the insulation, the heat loss is generallytoo high to be offset by a conventional heat tracingsystem.

Before the thermal insulation is installed on a heat-traced pipe, the tracing circuit should be tested fordielectric insulation resistance. This will ensure thatthe cable has not been damaged while exposed onthe uninsulated pipe.

In addition to piping and in-line equipment such aspumps and valves, all heat sinks must be properlyinsulated. This includes pipe shoes, hangers,flanges and, in many cases, valve bonnets.

There are many different pipe insulation materials,each of which has advantages in particular appli-cations. Regardless of the type or thickness ofinsulation used, a protective barrier should beinstalled. This protects the insulation from moistureintrusion and physical damage and helps ensurethe proper performance of the heat tracing system.

Notes . . .

• When rigid (noncompressible) materials are used, the inside diameterof the insulation is usually oversized to accommodate the heating cableon the pipe.

• Insulating materials are very susceptible to water absorption, whichdramatically increases the heat loss and should be replaced if the ma-terials get wet.

3

Inspection Report Form for Electric Heat Tracing (Typical)

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TroubleshootingThe following information is intended to assist in troubleshooting electric heat tracing systems. Theprimary objective is to provide an enhanced understanding of the elements of a successful heat tracinginstallation. Of these elements, one of the most important is the thermal insulation.

Before calling the heat tracing vendor, make a visual inspection of the installation; perhaps the thermalinsulation is wet, damaged or missing. Also consider the possibility that repairs or maintenance of in-lineor nearby equipment may have resulted in damage to the heat tracing equipment. These are commoncauses of tracing problems which are often overlooked. Other possible causes are listed below with theirsymptoms and remedies.

If an electric heat tracing circuit is suspected to be damaged, a dielectric insulation resistance (megger)test should be performed using a 2500 Vdc megohmmeter for polymer-insulated heating cables or 1000Vdc for MI cable. Periodic testing with accurate records will establish a “normal” range of operation (referto the Inspection Report Form on page 3). Dielectric insulation resistance readings which deviate fromthe normal range can quickly reveal a damaged circuit.

Symptom Possible Cause Remedy

I. No heat/no current A. Loss of power (voltage)

B. Controller setpoint too lowC. High temperature limit switch

activatedD. “Open” series heating circuitE. Controller failure

A. Restore power to tracing circuit(check circuit breaker and electricalconnections). Poorly made termina-tions can cause EPD-type breakersto trip unexpectedly

B. Adjust setpointC. May require manual reset to re-

enable heat tracing circuitD. Repair or replace circuit1

E. Repair sensor or controller2

II. Low system temperature A. Controller setpoint too lowB. Temperature sensor located too

close to heating cable or other heatsource; may be accompanied byexcessive cycling of control relays/contacts

C. Insulation material and/or thicknessdifferent than designed

D. Ambient temperature lower thandesigned

E. Low voltage (check at powerconnection point)

A. Adjust setpointB. Relocate sensor

C. Replace insulation; increaseinsulation thickness (if dry);consider increasing voltage forhigher cable output3

D. Install higher output heating cable;increase insulation thickness; raisevoltage3

E. Adjust voltage to meet designrequirements3

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Symptom Possible Cause Remedy

Notes . . .

1. Flexible, plastic-jacketed heating cables may be field-spliced; MI cables usually require replacement.

2. Mechanical thermostat sensors cannot be repaired or replaced; RTD or thermocouple sensors can be replaced. Some controllers have replaceablecontacts/relays or may require a manual reset if a “trip-off” condition on the heating circuit was detected.

3. The operation of most electric heat tracing cables is dramatically affected by changes in the supply voltage. Before making any changes, consult thecable manufacturer with information on the alternate voltages available. Otherwise, cable failure and/or an electrical safety hazard may result insome situations.

III. Low temperature insections

A. Wet, damaged or missing insulation

B. Parallel heating cable; open elementor damaged matrix

C. Heat sinks (valves, pumps, pipesupports, etc.)

D. Significant changes in elevationalong length of the heat-traced pipe

A. Repair or replace insulation andjacket

B. Repair or replace; splice kits areavailable from cable manufacturer

C. Insulate heat sinks or increaseamount of tracing on heat sinks

D. Consider dividing heating circuitinto separate, independentlycontrolled segments

IV. High system temperature A. Controller “on” continuouslyB. Controller failed with contacts

closedC. Sensor located on uninsulated pipe

or too close to heat sink

D. Backup heating circuit controller“on” continuously

A. Adjust setpoint or replace sensor2

B. Replace sensor or controller2

C. Relocate sensor to an area repre-sentative of conditions along entirepipe length

D. Adjust setpoint or replace backupcontroller

V. Excessive cycling A. Temperature sensor located tooclose to heating cable or other heatsource; may be accompanied bylow system temperature

B. Ambient temperature near con-troller setpoint

C. Connected voltage too highD. Heating cable output too high

(overdesign)E. Controller differential too narrow

A. Relocate sensor

B. Temporarily alter controller setpoint

C. Lower voltageD. Install lower output heating cable or

lower voltageE. Widen differential or replace con-

troller to avoid premature contactfailure

VI. Temperature variationsfrom setpoint alongpipeline

A. Unanticipated flow patterns orprocess operating temperatures

B. Inconsistent cable installation alongpipeline

C. Inconsistent cable performance

A. Redistribute heating circuits to ac-commodate existing flow patterns;confirm process conditions

B. Check method of cable installation,especially at heat sinks

C. Compare calculated watts/foot[(volts x amps) ÷ length] for themeasured pipe temperature withdesigned cable output for the sametemperature; regional damage toparallel cable can cause partialfailure

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THERMON . . . The Heat Tracing Specialists®

100 Thermon Dr. • PO Box 609 • San Marcos, TX 78667-0609Phone: 512-396-5801 • Facsimile: 512-396-3627 • 800-820-HEATwww.thermon.com In Canada call 800-563-8461