Shrink Polymer Systems for heatshrink cable joints and terminations

As an ISO certified company, we have an obligation to investigate any of our product failures, but over the years we have been asked more and more to get involved in general failure analysis. We undertake to make an un-biased investigation into any failure involving cable joints and terminations regardless of who manufactured the product.

Case 5 - A cable box reported as “buzzing”

A cable box in the basement of a London news organisation was reported as “buzzing”.

The box contained 2 x 11kV XLPE terminations entering from the side. Both terminations were removed and sent to us for investigation.

Both had crossed cores and the spacing between cores was less than ideal. On the first termination the investigation showed the insulation to have been damaged when removing the “peelable” extruded screen. However, this did not show signs of activity and although this was a potential problem, it was unlikely to be the cause of the noise.

Examining the anti tracking tubing on the second termination showed signs of erosion on two of the cores above the stress control area. These lined up and it would appear the two cores were in contact with each other whilst in service.

The cause of the “buzzing” was due to the cores in intimate contact with each other in an unscreened area, this would in time have eaten through the tubing and possibly caused the termination to fail.

An interview with the installer revealed, at the time of installation, there was more than sufficient clearance, but over time the cable had sagged and the gap closed.