Trace heating
Mineral insulated cables ran at high current densities to produce heat, and control equipment was adapted from other applications.
A similar principle can be applied to process piping carrying fluids which may congeal at low temperatures, for example, tars or molten sulfur.
Therefore, the net positive suction head (pressure difference) available can be raised, decreasing the likelihood of cavitation when pumping.
However, care must be taken not to increase the vapour pressure of the fluid too much, as this would have a strong side effect on the available head, possibly outweighing any benefit.
A series heating cable is made of a run of high-resistance wire, insulated and often enclosed in a protective jacket.
The downside of these types of heaters is that if they are crossed over themselves they can overheat and burn out, they are provided in specific lengths and cannot be shortened in the field, also, a break anywhere along the line will result in a failure of the entire cable.
The upside is that they are typically inexpensive (if plastic style heaters) or, as is true with mineral insulated heating cables, they can be exposed to very high temperatures.
A constant wattage cable is composed of multiple constant electric power zones and is made by wrapping a fine heating element around two insulated parallel bus wires, then on alternating sides of the conductors a notch is made in the insulation.
[2] The benefits of this system over series elements is that should one small element fail then the rest of the system will continue to operate, on the other hand damaged sections of cable (usually 3 ft span) will stay cold and possibly lead to freeze ups on said section.
It is more rugged, and much more reliable than a constant wattage cable; it cannot over-heat itself so it can be crossed over, but it is bad practice to install tape in this way.
For self-regulating cable, the supply must furnish a large warm-up current if the system is switched on from a cold starting condition.
The contactor or controller may include a thermostat if accurate temperature maintenance is required, or may just shut off a freeze-protection system in mild weather.
Electrical heat tracing systems may be required to have earth leakage (ground fault or RCD) devices for personnel and equipment protection.
The system design must minimize leakage current to prevent nuisance tripping; this may limit the length of any individual heating circuit.
