Do Prysmian Resin Cable Joints sometimes fail over time?

dlongson · Mar 21, 2023

Hi
A professional electrician installed power to an outside greenhouse about 6-7 years ago. The supply has very recently developed a recent RCD tripping fault. By process of elimination, the overwhelmingly likely place for the fault is a N-E leak in a Prysmian Resin Cable Joints between two SWA cables which I found buried in the greenhouse (and pretty 'damp' on the outside!).

Replacing the joint is a bit of an endeavour, so before getting the work done, I'd like to ask if these joints are known to fail? It 'looks' solid enough, and in many respects I'd be surprised if it has failed as it "looks" well done, and the rest of the installer's work has always been very solid. It gets hot and humid in a greenhouse though...

Cheers
Damien

westward10 · Mar 21, 2023

Any joint is prone to failure but resin joints are generally very reliable as the resin encapsulates the joint.

pc1966 · Mar 21, 2023

N & E are normally at a very similar voltage so not as prone to shorting out as a result of damp, you would usually see L-E (trips RCD at low levels) or L-N (trips over-current so bigger bang). Resin joints are generally good if done properly and 6-7 years suggests nothing too obviously wrong to begin with.

However, mechanical damage can do that and it could be a stone pushed in to the SWA cable somewhere that is causing it. Do you know if the cable was put in duct or buried direct in the ground? If so, was sand used for initial back-fill?

More obviously, has any digging work taken place close to the run of the cable?

If you have a definite low resistance N-E short there are ways to get a reasonable guess as to where it is, but if it is a modest resistance from a poor (but still bad to have) fault then pinning down where along the cable it is can be almost impossible and you usually have to split at junctions and check which segment is at fault, etc. Obviously having eliminated any accessories first.