Filkab: The anatomy of electrical installation durability, or why environmental conditions deteriorate inappropriately selected cable

If you’ve ever had to pull out a cable, which has been buried for a couple of years, you know how an unsuccessful attempt looks like: cracked, peeling outer layer, falling apart to the touch and metal that’s started to go green due to oxidization. This is the natural fate of every installation, in which the gray PVV-M was forced to do the job of the black SVT. And no, it's not about manufacturing quality, it is a matter of chemistry.

One of the greatest myths in the world of electrical installation is that once the cable is hidden in the tube, its type doesn’t matter. This is not reliable. PVC (polyvinyl chloride) used for the outer layer of PVV-M cables is a hygroscopic material. The structure consists of microscopic gaps, which under constant humidity (even under condensation inside the tube), begin to fill. This diffusion process is irreversible and when the moisture penetrates deep enough, under the influence of the electric field, the so-called "water treeing" appears.

"A common misconception is that the corrugated pipe saves PVV-M. In reality, if the pipe floods or fills with condensation, the cable remains literally soaked in a water bath. Because NYM does not have the chemical barrier of NYY, the cable begins to "drink" moisture from the environment. Eventually, the residual current protection starts to trip for no apparent reason and the only solution is demolition and new excavation," explained BalkanEngineer.com from Filkab, leading distributor and engineering partner in the power sector, whose expertise is based on decades of experience and the supply of materials for some of the most complex industrial sites.

In comparison, the SVT (NYY) has a sheath made of reinforced PVC plastic. It is designed to withstand hydrostatic pressure – the pressure against the cable because of wet soil. The molecular chains are more tightly intertwined, thus making water penetration practically impossible. Even with partial flooding, SVT retains its insulation resistance within standards for decades.

Photo source: Filkab, Philips, ©Engineer.BG via Canva.com