Last week in LinkedIn, I came across a post where the cable was “preheated” with an open fire before laying. Workers “heated up” beautiful cable with open fire and at the same time cheerfully said, “How good that we have a cable with a non-flammable outer sheath”. I couldn’t get past such a terrible attitude towards cable, and decided to make a short post on this topic.

Laying cables at low temperatures is dangerous because the cable loses its flexibility, and its outer sheath (jacket) may crack, as shown in the photo (1).

If the cable temperature is less than -5°C, then it is better not to lay the cable at all (for some types of outer sheath, this temperature value is -10°C). If it is not possible to postpone laying the cable until warmer weather, then the cable should be heated up before laying.

Preheating the cable with an open flame (2) is strictly prohibited, regardless of the design of the cable outer sheath (whether it is flammable or not). Warming up should be carried out slowly, indoors or in a created shelter (for example, under a tent) using a heat gun (3). The heat gun can be oriented directly at the coils of the cable, but it is not allowed that the temperature of the cable outer sheath exceeds 80°C, what should be strictly monitored.

Heating cable up should be long-term and gradual. For example:
✅ 72 hours, at a temperature of 5-10° C in the shelter;
✅ 24 hours, at a temperature of 10-25° C in the shelter;
✅ 18 hours, at a temperature of 25-40° C in the shelter.

It is important that after the cable is heated up, depending on the outside air temperature, the cable laying should be completed in no more than 1.0-1.5 hours. If the work is not completed during this time, then you will have to heat up the cable along the entire cable route, which is much more difficult than heating up one drum in one shelter.

That’s probably all I want to say. Unfortunately, cable preheating is not covered in the book, but there is Part 5 in the book “High Voltage Cable Lines” that explains why the cross-section of cable screens should be chosen not only according to the conditions of thermal stability, but also according to the conditions of non-self-ignition. Read it, it provides a sufficient number of explanations.