Electric heat tracing systems have been around for many years. Originally they were in the form of series resistance, constant watt output heaters, like mineral insulated (MI) cables. This style of heater had to be manufactured to suit pipe length, output required and available supply voltage. Changes in any of these criteria would result in re-design.
However, technology advanced and parallel resistance, constant watt output heaters, that could be cut to length without affecting the watts per metre output were developed.
The two main types of trace heating are constant wattage & self regulating
Self Limiting heating tapes, have a semi-conductive heating core matrix, the resistance of which changes in relation to the temperature of the heating tape are very popular for heat tracing applications.
Early sales and marketing information also suggested that thermostatic control was not required. This is still the view of many potential users, although those more experienced have learned that a thermostat control can reduce system operating costs by as much as 90%!
The generally accepted view is that, whilst acknowledging the significance of their self-limiting characteristics, all such tapes, from whatever source, have shortcomings when used for process heating. This is one of the reasons why it is recommend that, if self-limiting tapes must be used, they are used only for low temperature freeze protection of pipes and other simple systems where critical temperatures are not involved.
Self regulating heating tape
The electrical characteristics of Self Regulating heating tapes are that as pipe/heating tape temperature falls under no-flow conditions or due to the decreases in external or internal temperature the electrical conductivity of the semi-conductive polymer core increases, causing the tape to increase output.
As the pipe/heating tape temperature increases under flow conditions or as a result of increasing external or internal temperature the conductivity reduces and output decreases.
These tapes are suitable for frost protection and low to medium process temperature maintenance.
Self regulating pros & cons
- As temperature increases, the cable output decreases
- Heating cables cannot overheat
- Easy to install
- Easy to terminate
- The matrix core can be irreversibly damaged if subjected to high temperatures
- Self limiting heaters cannot be tested and monitored for correct operation as the output, resistance & current consumption is constantly changing
- Self limiting heaters have very high start up currents at low temperatures
- Self regulating cables are less flexible than silicone insulating cables
Constant wattage heating tape
Constant wattage heaters exist in various forms, of which the more popular zonal parallel circuit devices are the most convenient, since these may be ‘cut to length’, within practical limits, on site.
The electrical characteristics and outputs of zonal parallel circuit heating tapes can be monitored and checked at all times throughout their installed life, either manually or automatically by current sensing systems.
All constant wattage heating tapes should be temperature controlled for efficient operation and control.
Constant wattage pros & cons
- Can generally maintain higher process temperatures
- Heater output is always close to the manufacturer’s specification
- Generally do not exhibit increased start up loads
- The nickel alloy heating elements are unaffected by high temperatures and are not affected by thermal cycling
- Monitoring constant wattage tapes is simple and effective using resistance monitors or ammeters
- East to install
- Easy to terminate
- Higher wattage systems can overheat if incorrectly designed and or installed
Engineers and installers using trace heating will always have their preferences as to the type of trace heating to use. This is why at ESH Trace Heating Ltd we offer a comprehensive range of both constant wattage and self limiting heating tapes, to allow the end user to utilise the system that best suits their application and personal preference.
Buy trace heating cable online @ www.traceheatingdirect.com