Two ways to make heat
Every heating cable turns electricity into heat, but the two most common families do it differently. That difference changes how they behave on a cold night, how they are installed and how much can go wrong.
Self-regulating cable has two parallel bus wires buried in a conductive polymer core. Current flows through the core between the wires. As the core warms up, it conducts less, so the cable puts out less heat. As it cools, output rises again.
Constant wattage cable puts out the same heat per metre no matter what temperature it is at. In the common zone type, a fine resistance wire spirals around two bus wires and taps onto them at set intervals. Series types use the conductor itself as the heater, so their length is fixed by design.
Both kinds have an outer braid and jacket. The braid gives a path to ground so the ground-fault protection can detect a damaged cable, and it adds mechanical strength. The jacket protects against moisture, UV and chemicals, and different jackets are made for different settings.
How each one behaves in the cold
Picture a long water line where one part runs through a warm mechanical room and another part runs through a cold, drafty crawl space. Self-regulating cable puts out more heat in the cold section and less in the warm one, all on its own.
Constant wattage cable puts out the same heat in both places. That makes control more important. A thermostat or controller has to decide when the whole circuit runs, and it cannot tell one section from another.
The self-regulating effect is local, metre by metre. Where the cable passes a pipe support, a valve body or a gap in the insulation that runs colder, that short section works harder. This is a big reason it is the default for freeze protection in buildings with mixed conditions.
Self-regulating cable also has a downside. It draws much more current when first switched on cold, which is called start-up or inrush current. Breakers and wiring must be sized for that, using the maker's tables for the coldest start-up temperature. In Edmonton that is a real design number, not a footnote.
Side by side
| Question | Self-regulating | Constant wattage |
|---|---|---|
| Output changes with temperature? | Yes, drops as it warms | No, stays the same |
| Can it cross itself? | Usually yes, if the data sheet allows | No, overlap causes hot spots |
| Cut to length on site? | Yes, in most products | Zone type yes, series type no |
| Start-up current | High when cold | Close to running current |
| Long runs | Limited circuit length | Can serve longer runs |
| Higher temperature work | Limited by polymer rating | Higher ratings available |
| Typical homes and small buildings | Most common choice | Less common |
Neither type is better in every case. Self-regulating cable is the usual choice for freeze protection in homes, small commercial buildings and roof and gutter systems because it is forgiving. Constant wattage cable earns its place on long pipelines and in some process heating work where predictable output and longer circuit lengths matter.
For very high temperatures or harsh industrial areas, mineral insulated cable is a third option. It is a specialist product with its own design rules, and it is covered in our process heat tracing work.
Installation rules that differ
Because constant wattage cable cannot back off its output, any place where it doubles back on itself, sits under extra insulation, or touches a surface it was not designed for can overheat. That is why spiral wrapping and valve loops are laid out with care.
Self-regulating cable is more forgiving, but not foolproof. It still has a maximum exposure temperature. Steam cleaning a line, or tracing a pipe that sometimes carries hot fluid, can damage a polymer core that is not rated for it.
Both types need ground-fault protection on the circuit under the Canadian Electrical Code. If a heat trace circuit keeps tripping, the cable or a termination is likely damaged. Do not replace the protection with a plain breaker.
How to choose for your building
A heat trace designer or experienced electrician will ask:
- What is being protected, and what temperature must it hold?
- What is the pipe size and material, and what insulation is on it?
- How long is each run, and where does it go?
- What is the lowest temperature it will see, including wind exposure?
- Will anything flowing in the pipe ever get hot, such as steam out?
- How will the system be controlled, monitored and maintained?
The answers point to a cable type, output rating, circuit layout and control strategy. They also decide how many circuits are needed and how much panel capacity the system will use.
Energy use belongs in the conversation too. Ask how the system will be switched: on air temperature, on pipe temperature, or by a building automation system. Ask whether the controller can alarm on a ground fault or a failed circuit, so a dead cable is found in November and not after a burst pipe in February.
If you have mechanical drawings or an insulation spec, share them at the start. It shortens design time and avoids guesswork about pipe sizes and routes.
Replacing old cable
Many older Edmonton buildings have constant wattage cable that was installed decades ago with little or no control. When it fails, owners often switch to self-regulating cable with a modern controller. That can cut energy use and lower the risk of burnout, but the circuits must be redesigned for start-up current.
Before replacing, confirm the insulation is still dry and intact. New cable under wet insulation will not perform. Our pipe heat tracing team can survey existing lines and recommend repair or replacement.
Common questions
Is self-regulating cable always more efficient?
It responds to temperature on its own, which helps, but good control matters more. A constant wattage system on a proper controller can run efficiently, and a self-regulating cable left on all year wastes power.
Can I cut self-regulating cable to any length?
Most products can be cut to length within the maximum circuit length listed by the manufacturer. Each end needs the correct listed power and end seal kits.
Why does my new self-regulating system trip the breaker on cold mornings?
It is probably start-up current. Cold cable draws much more at switch-on. The circuit may be too long for the breaker size, which an electrician can check against the data sheet.
Can I mix cable types on one circuit?
No. Each circuit should use one cable type with matching kits and controls, designed to the manufacturer's instructions.
Codes and permit rules change and every building is different. For work on your system, talk to a licensed electrician and your local permit authority.