Process Electric Heat Tracing System

This article is about  the minimum requirements for design, manufacturing, installation, and testing of electric heat tracing system.Main keywords for this article are Process Heat Tracing System, Heater Cable Types and Materials, Electrical Heat Tracing Control Panels, Electrical Heat Tracing Devices, Heat Tracing Tests.

Electric Heat Tracing, Cable, Panels and Accessories

Electric Heat Tracing References

Institute of Electrical and Electronics Engineers (IEEE)
515 Recommended Practice for the Testing, Design, Installation, and Maintenance of Electrical Resistance Heat Tracing for Industrial Applications
National Fire Protection Agency (NFPA)
70 National Electrical Code (NEC)
496 Standard for Purge and Pressurized Enclosures for Electrical Equipment

The design of the individual heat tracing systems shall be in accordance with Electrical Heat Tracing Design in Oil & Gas Industry. Tracing system shall comply with the requirements of IEEE-515All equipment and material shall be furnished in accordance with area classification requirement. Where traced pipes enter a building, the tracer shall extend a minimum of 3  feet inside the building wall, unless otherwise specified. 

Maintenance – Where equipment which is electrically heat traced, must be removed for maintenance, the heat tracing installed on the equipment shall be constructed such that it may be disconnected from associated heat tracing and power supply.

Process Heat Tracing System

A completely coordinated and integrated electrical process heat tracing system shall be provided. The process heat tracing system shall consist of the following main sub assemblies:
a. Process heat trace control panels:

(i) Main circuit breaker (*)
(ii) Power distribution panelboard (*)
(iii) Temperature controllers
(iv) Contactors or relays
(v) ’POWER ON” indicating light (red)
(vi) Main ammeter to indicate total load
(vii) Terminal blocks
(viii) Space heater
b. Power transformer (adjacent to each panel) (*)
c. Temperature sensors (RTD’s)
d. Electric heat tracers (**)
e. Power and control wiring and conduit to heaters

Heater Cable Types and Materials

Self-Regulating Heater Cable

  • The electric heater cable shall consist of two stranded copper  wires separated by a self-regulating semi-conductive core. The core shall be covered by an inner jacket of either fluoropolymer or thermoplastic rubber material, a tinned copper braid and an outer corrosion resistant fluoropolymer jacket.
  • The heater cable shall operate on standard voltages specified without the use of special transformers.
  • The design of the electric heat tracer shall be such that it can be cut to any length in the field without changing the heat output per foot and shall not result in any small section of the pipe being without heat.
  • The heat tracer must be capable of being overlapped on itself without causing localized hot spots or creating any hazards or possibilities of burn-outs. The heat tracer shall be capable of continuous and reliable operation when hanging loose in free air during equipment removal or replacement.
  • Failure of controls while the heat tracer is energized shall not raise the heat tracer temperature sufficiently to cause heat tracer failure.
  • Tinned copper braid shall be specified for installations where the surface does not provide an effective ground path (plastic, stainless steel, or painted surfaces) and where exposure to corrosives is not expected.
  • Tinned copper braid with an outer jacket shall be specified for use on installations in non-corrosive areas that do not provide an effective ground path (plastic, stainless steel, or painted surfaces) and where mechanical protection is required.

Mineral Insulated Heater Cable

  • Mineral insulated (MI) heater cable shall be two conductor type with copper or alloy heating wire, magnesium oxide insulation and copper, stainless steel or an Inconel sheath. Heater cable shall have proper resistance to develop the required watt density with the power supply specified. The complete heater assembly shall be Factory Mutual or UL approved for use in the hazardous areas defined in the Data Sheet(s).
  • Each MI heater cable shall be factory fabricated to required lengths with cold junctions for connection to power or where splices are required. Cold sections shall be 2 m long with 300 mm long THW insulated leads. Cold sections shall have gland type fitting for termination in threaded hub junction boxes. Cables shall be factory terminated and sealed.
  •  MI cable circuits exceeding 60 m in length shall be broken into sections of 60 m or less. Cable sections shall be interconnected in external splices boxes.
  • MI heater cables shall be attached to pipes on maximum 300mm centers by means of 16 gauge stainless steel tie wire.
  • Each MI heater cable shall have a stainless steel tag connected to the cold sections with stainless steel wire. The tag shall show the circuit number to which it is connected, Factory Mutual and/or UL approval, catalog number and heater electrical and physical characteristics such as voltage, watts/foot heater output, resistance and cable diameter.

Heater Cable Types and Materials

Main keywords for this article are Process Heat Tracing System, Heater Cable Types and Materials, Electrical Heat Tracing Control Panels, Electrical Heat Tracing Devices, Heat Tracing Tests.

Thermon MI Cable Reference

Thermon MI Cable Reference

Thermon MI Cable Reference

Thermon MI Cable Reference

Main keywords for this article are Process Heat Tracing System, Heater Cable Types and Materials, Electrical Heat Tracing Control Panels, Electrical Heat Tracing Devices, Heat Tracing Tests.

Electrical Heat Tracing Control Panels

  • Each control panel shall be housed in a NEMA 4X or NEMA 4/7  weatherproof, corrosion resistant enclosure, as applicable, to meet the requirements of the specified area classification.
  • When specified, an interior swing door assembly shall be provided for mounting of all controller, pilot lights, and control switches.
  • The panel enclosure shall be provided with thermostatically controlled space heaters and shall be complete with all required components including a main breaker, power distribution panelboard, contactors, relays, temperature controllers, control switches, indicating lights, terminal blocks, ground bus, and all power and control wiring internal to the panel. Provisions shall be made for pad locking of individual heater circuits for maintenance and testing.
  • Purging shall be used only when specified to allow NEMA 4X panel to be mounted in a Class I, Division 2 hazardous area. The purge system shall be in accordance with NFPA 496.
  • A white ‘LOSS OF PURGE’ alarm indicating light shall be provided on the panel, and a form C (SPDT) contact shall be provided for remote indication of alarm condition.

Electrical Heat Tracing Control PanelsElectrical Heat Tracing Control Panels

Process Heat Tracing SystemElectrical Heat Tracing Control Panels

Circuit Breakers and Distribution Panel

  • Main breakers and distribution panels shall be surface mounted on the back of each  control panel. Unless specified otherwise, distribution panels shall be 230/400 V with  a three pole main breaker rated at 125 percent of the transformer secondary current to which it is connected.
  • Branch circuit breakers shall be molded-case, 20 amp, single-pole, minimum 10,000 amp interrupting capacity. Twenty percent spare breakers shall be furnished in each panel.
  • For process heat tracing panels, 20 amp 2 pole branch circuit breakers may be used in those cases where 208 V heating circuits are advantageous.
  • Single pole branch breakers, 15 amp, may be utilized if required for control power and/or space heater circuits in the process heat tracing panels.
  • Ground fault equipment protection with a nominal 230/400 Vac , 30 mA trip is required for each circuit breaker in accordance with the NEC Art. 427.

Contactors

Contactors shall be open type, electrically held, with 120 VAC coil  and normally open contacts. Contactors shall be fully rated and designed to withstand in-rush currents associated with the type of heater cables used. Contacts shall be copper alloy with silver cadmium alloy contact buttons.

Each process heat trace control panel shall be provided with branch circuit contactors or relays. As a minimum, each branch circuit contactor or relay shall be rated 30 A with 3 pole construction. 

Electrical Heat Tracing Temperature Controllers

  • Temperature controllers shall be provided to operate heating  circuits.
  • Temperature controllers shall be individual microprocessor based  ‘ON-OFF’ type (not proportional switching mode) with set points corresponding to the required minimum holding temperatures.  
  • Controllers shall operate from a 230 V power supply. Input to each controller shall be from a field mounted, three-wire, 100 ohm platinum RTD.
  • Each controller shall continuously display the monitored temperature with an LED readout. Set point temperature indicators shall also be continuously displaced and must be adjustable without affecting the LED temperature reading. Displays shall be in degrees Celsius.
  • The controller range shall be adjustable from 0C to 399C with a minimum accuracy of 0.2 percent of span. Dead band shall be adjustable as required.
  • In addition to controlling the heater circuits, each controller shall have adjustable alarm features which are adaptable to different alarm configurations (i.e. low alarm, high alarm, low/high alarm, etc.). Each controller shall have a form C contact for remote indication of alarm condition.
  • Each controller shall also contain pilot lights for the following indications:
    a. ‘CYCLE ON’ (red)
    b. ‘CYCLE OFF’ (green)
    c. ‘ALARM’ (yellow)
  • Controller output contact shall have sufficient rating for operating the contactor 230 Vac coils.

Electrical Heat Tracing Temperature Controllers

CPSS Control Panels (Base Load – SCR)

CPSS Control Panels (Base Load - SCR)

CPE Control Panels

CPE Control PanelsElectrical Heat Tracing Tests And Inspections

CPG Control Panels Ground Fault Protection

Electrical Heat Tracing Tests And InspectionsElectrical Heat Tracing Devices

Main keywords for this article are Process Heat Tracing System, Heater Cable Types and Materials, Electrical Heat Tracing Control Panels, Electrical Heat Tracing Devices, Heat Tracing Tests.

Electrical Heat Tracing Devices

Panel mounted indicating lights, switches, auxiliary control relays  and other such devices shall be provided as required for proper operation of equipment in accordance with the requirements of this specification.

Push buttons, selector switches and indicating lights shall be heavy duty oil-tight type. Indicating lights shall be push-to-test type.  Control relays and timers shall be plug-in, tube base type with screw terminal tube base sockets. Each relay shall have a minimum of two form C contacts with a  minimum rating of 5 amps at 230 Vac.

Remote Alarms

  • All contacts specified for initiation of remote alarms shall be wired  together to provide two single remote alarm functions. The (fault and temperature control) alarm contacts shall be wired each to a single set of terminals which shall be provided for external alarm wiring connections.
  • The functions which shall actuate remote alarm system shall include but is not limited to the following:
    a. Loss of Purge
    b. Controller Alarm

 Terminal Blocks

  • Terminal blocks shall be provided for terminating all power, control  and instrument wires entering each control panel.
  • Terminal blocks shall be rail mounted, modular type with tubular screw pressure plate wire connections. Termination of control and power wires shall be by lugs. Terminals for power shall have a minimum rating of 600 V with a minimum ampacity of 55 amps.
  • Each utilized terminal point shall be permanently marked as identified on the electrical drawings. A minimum of 20 percent spare terminals shall be provided.
  • All shield drain wires for instrument cable shall be terminated on terminal blocks located adjacent to the cable conductor terminals. All shield terminals shall be connected to the control panel ground bus. Shields shall be grounded only at the control panel.   

Control Panel Wiring

  • Control panel power and control cables shall be single conductor  XHHW, 4 mm2 (12 AWG) and 2.5 mm2 (14 AWG) respectively.
  • Control panel RTD instrument cables shall be single triad.
  • Control panel wiring shall be installed in a neat workmanlike  manner and shall be mechanically supported as necessary to hold  in place.
  • Wiring shall be suitably protected from abrasion caused by rubbing against sharp edges, door hinges, bolt threads, etc.
  • Separation shall be maintained between instrument wiring and power/control wiring.
  • All wiring connections shall be easily accessible. Backconnections shall be used only for equipment mounted on swing panel. All other wiring shall be front-connected.
  • Electrical wiring and wire marking shall be in exact conformance with the approved drawings.
  • Wires shall be identified on each end and at all connections. Wire markers shall be white heat shrink with black permanent identification.
  • A separate neutral conductor shall be wired out for each individual branch circuit breaker. Separate neutral wires shall be maintained all the way to the heater cable connections for each branch power circuit.

Space Heaters

  • Thermostatically controlled space heaters with manual bypass  switch shall be provided in each control panel to prevent condensation. A molded case circuit breaker shall be provided for each heater circuit for overload protection and disconnecting means.
  • Space heaters shall be operated on 230 Vac.
  • A blue indicating light shall be provided on the enclosure door for each space heater to indicate that the respective space heater power is available.
  • Control and Space Heater Power Supplies
  • In the process heat trace control panels, 230 Vac control and space heater power supplies shall be provided from individual branch circuit breakers in the power distribution panel board.
    Supplementary fusing shall be installed for the control circuits if required to provide adequate protection.

Control Panel Ground Bus

  • A copper ground bus shall be installed at the bottom of each  control panel assembly and shall be solidly bonded to the panel enclosure.
  • The ground bus shall be minimum 6 mm by 25 mm copper and shall extend across the entire width of the enclosure. The ground bus shall be provided with two main lugs (one at each end) for connection of 70 mm² copper cables to the plant ground grid.
  • All instrument cable shields and all equipment ground wires  entering the control panel shall be connected to the ground bus using bolt-on grounding lugs.
  • The neutral bus in the power distribution panelboard shall also be connected to the ground bus. The neutral ground connection shall be made with the same size cable as the incoming neutral from the power transformer.

Drawing And Data Requirements

a. Outline and Arrangement Drawings – Outline and arrangement drawings shall be completely dimensioned and shall indicate the following:
(i) Plan, front elevation, and other elevations, if pertinent.
(ii) Equipment arrangement.
(iii) Required clearances.
(iv) Location and size of all conduit entrances (top and/or bottom) for Purchaser’sconnections.
(v) Power cable terminator positions.
(vi) All terminal block locations including those for Purchaser’s connections.
(vii) Anchor bolt hole size and location, and recommended minimum anchor boltsize.
(viii) Ground connections.
(ix) Weight of equipment.
b. Elementary Wiring Diagrams
(i) Elementary diagrams shall show all control devices and device contacts, each of which shall be labeled with its proper ANSI device function number.
(ii) Terminals of all devices and terminal blocks shall be numbered.
c. Connection Diagrams
(i) Connection diagrams shall indicate the approximate physical location of all items in each assembly.
(ii) Connection diagrams shall indicate all wiring within each assembly and all interconnecting wiring between assemblies.
(iii) Connection diagrams shall identify all terminals, terminal blocks, and wires.
(iv) Connection diagrams shall clearly identify all wiring which is to be installed by the Purchaser.

Electrical Heat Tracing Tests And Inspections

  • The electrical heat tracing components and overall system shall be tested in accordance with the requirements of IEEE 515, Section 5. Tests shall meet the performance and test criteria of these standards.
  • Factory inspections and tests for self-regulating heater cables shall include but not be limited to the following:

a. Dry dielectric spark tests at 6000 V shall be performed on every foot of material shipped.
b. Resistance shall be checked as a function of temperature for every shipped length to ensure maintenance of proper heater characteristics.
c. Hand inspection shall be made on every foot of material shipped for cosmetic factors or visually detectable manufacturing defects.

  • Factory inspections and tests for constant wattage (MI) heater cables shall include, but are not limited to, the following:

a. Finished MI heater cables shall be inspected for proper diameter and checked for electrical continuity.
b. MI heater cables shall be subjected to and must withstand a 2500 V high-pot test after soaking in water for 24 hours.
c. Factory test documents of production tests performed may be checked.

Main keywords for this article are Process Heat Tracing System, Heater Cable Types and Materials, Electrical Heat Tracing Control Panels, Electrical Heat Tracing Devices, Heat Tracing Tests.

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