Earlier on the blog, we discussed how you could prepare your plant for winter with tips on winter safety in industrial applications. Today, we’re discussing how to do maintenance when a fault is found on self-regulating heating cables.
In the case of a fault on a heat tracing cable, approach with caution. Some of the first steps to take include checking to see if the correct work permits are in place, disconnecting the power from the circuit and verifying with a voltmeter. Check that no (field) thermostats are in between the electrical panel and the heat tracing cable. In case a (field) thermostat is present, always disconnect the power cables on both sides, and insulate the wires, so you don’t get false readings.
We suggest dividing the problem into three sections, to be followed in order. These include addressing the power cable, the heating cable and the thermostats. Follow these steps below in order to conduct proper field maintenance:
- Disconnect the power cable in the panel and insulate the wires.
- Open the power junction box in the field and disconnect the heat tracing cable(s) from the terminals.
- Before starting the megger test, be aware of related risks, when testing trough a thermostat.
- Megger test the power cable between junction box and panel.
- In case of low IR value <10M ohm, make sure to check if no intermediate marshalling boxes are installed. If so, disconnect power cables and check each section of the power cables.
- Do a “loop check” on each of the power cable(s).
- In case of a defective power cable, repair or replace.
Heat Tracing Cable
- Megger test the heat tracing cable(s) from the power junction box
In case of low IR value <10M ohm, you can detect where the fault is through these steps:
- In a heat tracing cable
- Make sure that the heat tracing cable is only made out of one section. In case of T-boxes installed, disconnect the cable from the T-box and megger the individual sections.
- Walk along the line, vessel or instrument and verify that the heat tracing cable is not damaged. Since the majority of the cable will be covered by thermal insulation, the chance damage will be found is low. Try to discover when and where it was worked on and check if there were any instances of damage to EHT cable at that time.
- Another option is to use hand held cable fault locators, which will send a small electrical pulse in the heat tracing cable.
- In a junction box
- Occasionally, the defect is not in the heating cable, but rather in the terminals of the junction box. Moisture or water in the box can create an electrical leak path, resulting in the ELCB to trip. Check for signs of moisture in the box and check that the box can still be properly sealed.
- It is possible that the cables in the terminals may have poor or no connection if there was improper work done during stripping and connecting.
- In the end seal
- Faults in end seals can occur but are rare. This is also an instance in which improper work can enable moisture or water to enter the end seal. If this scenario arises, replace the end seal.
- In a heat tracing cable
- In case of a mechanical thermostat, use a voltmeter to check that the internal relay is still switching on and off. Replace in case of defect.
- For electronic thermostats, it may be necessary to take extra safety precautions, as a voltage needs to be applied on the thermostat.
- By simulating a low temperature with a resistor or turning the thermostats set point higher, the thermostat will switch on.
- Verify with a voltmeter that the contactor inside is switching. Make sure to return the set point to its original value after the test.
Remember: these steps are a brief overview of how to conduct fault finding on heat tracing cables. Always follow specifications specific to your manufacturer and local safety rules. If you are unsure or uncomfortable following these steps, please contact a local professional to conduct the examination.