It is not always possible to choose the right heating cable type unequivocally. First, it is necessary to select a cable construction type.
Serial resistance heating cables
Serial resistance heating cables are not practically used for the heating of pipelines and other technologies anymore. Despite their low price they are devalued mostly because of the need to use various ohmic values for various pipeline length. If we don´t use a double-core heating cable or a cable with a regressive conductor (KYCYR) it is further required to create a loop in the cable and power it from one place. Another significant disadvantage is a lower operational reliability. If even a slight resistance element is shut off, then the whole loop ceases to function. Only in the case of long heated pipelines it is right to use sturdy serial resistance heating cables C1FS/I – C2FS/I – R3FS/I for long pipelines, which decrease the number of power-supply spots (after 1.5km). These cables are manufactured on commisions for specific applications.
Heating cables with constant capacity
Heating cables with constant capacity are parallel cables. This type is always powered from one side a it is possible to shorten it on the installation site to the desired length. A heating cable with constant capacity is cheaper compared to the auto-regulating cable and it is easier to achieve high temperature resistance with it. Though, it mostly requires regulation with a sensor on the pipeline and in the heating of plastic pipes it is necessary to choose a lower capacity (10 to 15W/m), to prevent damage to the pipe. The FTP heating cable with PVC insulation is designated for lower temperatures (up to 90°C), most of all as an anti-frost pipeline protection. The FTSH and FTTH series heating cables find use in maintaining higher operational temperatures (up to 200°C) or as an anti-frost protection of steam pipelines (impulse pipelines). The FTX 10 version is suitable for in-pipe installation thanks to its inner XLPE housing. The pair of more delicate cables FTP0 and FTS0 is designated primarily for cold storage industry as an anti-frost protection. The ZFE/CGE/ATEX and ZFA/CGA/ATEX cables with constant capacity have a complete fluorinepolymer FEP, resp. PFA insulation and it is possible to use them in environments with a danger of explosion.
Auto-regulating heating cables
Auto-regulating heating cables are also parallel heating cables. In addition to the shortening possibility and power from one side, we have the ability of auto-regulation. The capacity of these heating cables changes depending on the temperature. The heating cable then supplies only as much heat as is required, based on the momentary thermal conditions in each spot and significantly saves electrical power. Theoretically, there is no need for other regulation. Thanks to these qualities, auto-regulating heating cables are the most popular type for pipeline heating. For anti-frost protection, the most frequently used types are the FSG, or the more sturdy FST industrial auto-regulating heating cables for lower temperatures (up to 65°C). The FSX type is in its off-mode, resistant to temperatures up to 200°C, enabling for example to scour the pipe with steam. All these industrial auto-regulation cable types are designed with braidings, eventually an outer coat, which are approved for use in an environment with an explosion risk. The FSH type is designated for the HW temperature maintenance and protection from Legionella (vast objects, hospitals). When designing the heating using auto-regulating heating cables, it is necessary to count in a higher starting current and set the power supply based on this. The starting currents of each type are listed in the catalogue. Operation the auto-regulating heating cables at the boundary of their maximum allowed temperature substantially shortens their durability (cumulatively 1000 hours).
The previously mentioned heating cable types (auto-regulating and with constant capacity) are manufactured in various capacity variations and can be provided with more protective layers. The basic version of the heating cable can be fitted with braiding for a higher mechanical and electrical resistance. We´re talking either about a tin-plated copper braiding or a stainless steel braiding with an increased chemical resistance. Furthermore, heating cables can be equipped with an inner thermoplastic coating (PVC) for mechanical and chemical protection from water-based compounds. The fuorinepolymer coating ensures a thermal resistance up to 200°C and a chemical protection from carbon-based compounds. Parallel heating cables show a much higher operational reliability than serial cables. It is granted mostly by their sturdyness - the power conductors have a bigger diameter than the resistor conductor of the serial cables - the cables can sustain a greater load in pulling. If the parallel heating cable is locally damaged, the rest of the cable will function normally if the insulation status is not disrupted or the power conductor is not cut off. The maximum length of the heating cable is dependent on the cable type and is based on the diameter of the power conductors of the cable and its capacity value.
Table of heating cable insulation resistances against some chemical materials
