Chromalox SRL Self-Regulating Heat Trace Cable

Self-regulating heat trace cable for freeze protection and temperature maintenance

The Chromalox SRL is a self-regulating low-temperature heating cable for freeze protection and temperature maintenance of pipes, valves, tanks and similar equipment. Its semiconductive polymer core changes output along the cable in response to the local temperature, so it can be laid on metal or plastic pipe and can be single-overlapped around valves and supports without burnout. The cable is flexible, can be cut to length and spliced in the field, and is supplied for 120 V and 208 to 277 V supplies.

Four output grades cover typical designs: SRL 3, SRL 5, SRL 8 and SRL 10, nominal watts per foot at 50 °F, each with a 1 (120 V) or 2 (208 to 277 V) suffix, such as SRL 8-2. A high-temperature fluoropolymer or TPR overjacket over the braid is optional to protect against chemical attack and mechanical abuse.

Technical specifications

Output and circuit length

Maximum circuit length depends on the model, breaker size and start-up ambient. For a 50 °F start the sheet allows the following lengths per breaker rating; colder start-up temperatures and larger breakers have their own rows in the sheet.

Ordering and design notes

Order numbers combine the model with the cable construction code: SRL 3-1 CT (PCN 383400), SRL 3-2 CR (PCN 382740), SRL 5-2 CT (383451), SRL 8-2 CT (383478), SRL 10-2 CR (382854) and the other combinations listed in the sheet, where the CT and CR codes carry slightly different dimensions and weights. Connection kits in the U, DL and EL series cover power connection, splice and tee, end seals and ambient or line-sensing thermostats.

Heat loss from the pipe must be calculated for the design ambient, insulation and maintenance temperature, using Chromalox ChromaTrace software and design guide PJ130. Confirm the supply voltage, the start-up temperature, the circuit length against the table, the T-rating needed in a classified area and the ground fault protection. See more equipment in HVAC and combustion.

How self-regulation works in practice

Inside the SRL cable, the conductive polymer between the two bus wires forms a continuous parallel heating element. As the surrounding pipe cools, the polymer contracts microscopically, more conductive paths form and the cable delivers more heat. As the pipe warms, the polymer expands, conductive paths open and output falls. Because each short section responds to its own local temperature, a run that passes from a shaded rack into direct sun, or from an insulated line onto a cold valve body, automatically adjusts along its length without any additional control.

This behaviour is the reason the cable can be overlapped once at flanges and valves, and why it can be cut at any point without changing the output per foot. It does not replace a thermostat where energy saving or tight temperature control is needed, but it removes the risk of hot spots that constant-wattage cables can create.

Key features

• Four output grades from 3 to 10 W/ft nominal, so the heat delivered can be matched to the calculated pipe heat loss rather than oversized.
• Parallel circuit construction: cut to length on site, with no need for factory-terminated sets.
• Tinned copper braid that provides a ground path for ground fault protection and adds mechanical protection.
• Optional fluoropolymer or TPR overjacket for areas with chemical splash, hydrocarbons or abrasion.
• Approvals for ordinary and listed classified areas, with T-ratings that differ by model, an important point in process plants.

Selecting the right grade

Start from the heat loss per foot of the pipe at the minimum design ambient, which depends on pipe size, insulation type and thickness, and the temperature to be maintained. Choose the lowest SRL grade whose output at the maintenance temperature exceeds that loss with a reasonable safety factor. Where one grade is not enough, two parallel runs or spiral tracing may be used, following the design guide. Check the circuit length table for the chosen breaker size and the expected cold start temperature, because inrush current of self-regulating cable is highest when energised cold.

Installation and maintenance tips

• Fix the cable to the lower quadrant of horizontal pipes with glass-fibre or aluminium tape, never with metal wire ties that can cut the jacket.
• Respect the minimum bend radius and avoid installation below the stated minimum installation temperature.
• Use only the matching Chromalox connection kits for power, splice, tee and end seal; a cut cable end left unsealed lets moisture into the core.
• Install weatherproof insulation with a jacket and label the line as electrically traced.
• Measure insulation resistance before insulating, after insulating and at each annual inspection, and record the values to spot deterioration early.

Applications in Oman and the GCC

In a hot climate, freeze protection is rarely the main reason for tracing. More often SRL cable is used to keep viscous fluids, such as heavy fuel oil, molasses, waxy crude condensate or chemical solutions, above a temperature where they flow, to prevent crystallisation in caustic or sulphur lines, and to protect instrument tubing and safety showers in mountain areas or desert sites where night temperatures fall sharply in winter. Note that the maximum exposure temperature with power off must not be exceeded by steam-out or solar heating of black-jacketed pipes.

What to send with an RFQ

• Model and voltage suffix, for example SRL 5-2, and construction code CT or CR.
• Total cable length and the number of circuits, so that connection kits can be counted.
• Hazardous area classification and required temperature class, if applicable.
• Any thermostat or controller requirement.

Documents and quotation

The Chromalox SRL data sheet (EHT-DS-SRL) is attached. Seven Star LLC, an independent supplier in Muscat, quotes by model, construction code and length; stock and lead time are confirmed at quotation.