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What are the different types of trace heating?

Constant wattage, self-regulating and series resistance trace heating differences

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What is the difference?

So right now you may be thinking that there can’t be much difference between the 3 types of heat trace systems, ‘there all just wires that carry an electrical current and produce heat’ may be just one of the thoughts that has crossed your mind. Believe it or not there are some crucial differences in regards to the types of heat trace systems available with major dividing factor being the different types of cable used. Below we will explore what makes these trace heating cables different and the benefits for each type. For more information on our trace heating services and the 2 most common applications of trace heating click here.

Constant wattage

Constant wattage trace heat cables consist of 2 insulated bus wires which transmit the electricity, one being live and one being neutral. These bus wires are then wrapped in a heating element that converts this electricity into heat. The heating element is soldered to the bus wires, alternating between the live and neutral wires. This is done at various points across the cable which then create areas known as power zones or heat zones. These zones then act as individual fixed resistant circuits that are supplied with a fixed voltage and transmit a fixed wattage. 

You do find different kinds of constant wattage cables but this is the commonly seen format due to the parallel running bus wires and circuits offering increased flexibility.

Self-regulating

Self-regulating cables are also known as self-regulating tape. The key selling point of using self-regulating cables for trace heating is they automatically adjust their output depending on the temperature of their surroundings. For example if the temperature of a pipe falls then the thermal energy output of the cable rises and vice versa.

Self-regulating cables are made of 2 bus wires which are then encased in a semi-conductive polymer, this polymer is infused with carbon. This carbon infusion is what allows for the self-regulating qualities, the reason behind this is that when the polymer heats up the carbon will reduce the conductivity allowing for less electricity to pass through and less thermal energy to be produced. The opposite happens when the temperature drops. 

Series resistance

Series resistance cables are also known as constant power cables, they’re less common nowadays due to technological advancements and the increasing popularity of the other two options.

Series resistance cables consist of one wire made of a high resistant material, when an electrical current passes through this wire it then produces thermal energy due to the wire’s resistance. The wire is also insulated and then covered with a protective case, this is done to prevent the risk of electrocution and to protect the wire itself.

For another method of keeping water inside a pipe at a desired temperature, check out our pipe lagging page.

Advantages and disadvantages of each type

Constant wattage

+ves:

  • All constant wattage cables are installed with a thermostat to monitor and control the power output, making them adaptable and user friendly.
  • Constant wattage cables can be cut to length on field due to the parallel circuitry, making them easier to install and easier to make modifications to at a later date.
  • Even if the cable becomes damaged, only the damaged area will cease to work and the rest of the cable will remain functional. This is because the damage will only affect that specific power zone, which will then become a cold spot and produce no thermal energy.

-ves:

  • Constant wattage cables can be prone to overheating if the cable overlaps on itself or if the temperature isn’t monitored at regular intervals.
  • Constant wattage cables are not as efficient as self-regulating cables because they omit the same level of heat output despite their surroundings.
  • If the constant wattage cable used is of poor quality then the points where the heating element is soldered to the bus wires can disconnect. This then leads to cold spots throughout the cable due to broken power zones.

Self-regulating

+ves:

  • As self-regulating cables control their own temperature, there is little chance of them overheating or burning out. This adds an element of increased safety, security and reliability.
  • Self-regulating cables have a higher level of efficiency in comparison to their counterparts, this is because they only use the energy required due to their self-regulating quality.
  • As is the case with constant wattage cables, self-regulating cables can be cut to size on the field due to their parallel circuitry.

-ves:

  • Self-regulating cables normally aren’t able to withstand the same high temperatures as constant wattage cables. As a result, although they will not cause themselves to overheat they’re more susceptible to overheating because of external forces like excess heat from the pipe and the fluid pipes contain.
  • Another disadvantage of self-regulating cables is they’re not as adaptable or as easily controlled. For example, if a fixed temperature is required it will not be achievable with this cable type due to it’s self-regulating quality. Also if you want to alter the thermal energy output a new cable would have to be installed with a different proportion of carbon in the polymer.

Series resistance

+ves:

  • The main benefit which leads to people choosing series resistance cables is that they’re fairly inexpensive in comparison to their counterparts. This is due to their simplistic nature.
  • Series resistance cables are capable of handling much higher temperatures in comparison to the other types of trace heating cables, especially if they’re minerally insulated. This quality makes them especially suited to maintaining high temperatures on long pipe lines or maintaining low temperatures on extremely hot pipe lines (e.g. steam lines).

-ves:

  • A major issue with series resistance cables is the fact they can’t be cut to length or shortened on the field. Series resistance cables are made to specific lengths and any modification to this will break the circuit, leaving it inoperable. This makes them less adaptable to dynamic circumstances and more difficult to install.
  • Series resistance cables can be seen as less reliable than other forms of trace heating. The reason for this lack of reliability is because if any damage occurs to the cable that breaks the circuit it will cause the entire cable to become inoperable and need replacement.
  • Due to their absence of self-regulating qualities, series resistance cables are much more prone to overheating. This is especially the case if the cables have been made to overlap upon installation.