Case Study - Electrical Shroud Failure

Smithers Rapra were asked to provide an independent assessment of the condition of elastomeric shrouds around electrical connections.

History

Outdoor mains electrical connections require protection against rainwater ingress. Conventionally this is achieved by the tight fitting of elastomeric shrouds. The shrouds cannot be replaced without Electrical disconnection & for this reason there is a tendency to ignore the first visible signs of degradation & to delay replacement based on the impact of cost.

In this case a 30 year old electrical installation failed at a cold store. By the time the problem was detected, & the fault traced & repaired, the contents of the store had perished. The store owners submitted a substantial claim to their insurers. This was promptly settled but reinsurance would depend upon an independent evaluation of the condition of the installation.

Inspection & Analysis


Figure 1 A PVC shroud after 30 years service without direct exposure to sunlight

At the time of the inspection the cold store that had failed had been rewired & the original wiring disposed of. At interview the owners were suspiciously vague about the location where the failure occurred. Detailed inspection of the brickwork however revealed burn marks behind a new external junction box. This discovery was sufficient to remind the owners of the exact failure location.

The burn marks contained orange coloured debris, this material was collected & via FTIR analysis was found to be dioctyl phthalate (DOP) plasticised PVC.
Further investigation revealed old junction boxes with orange coloured shrouds in other parts of the site. Analysis revealed that these were also DOP plasticised PVC. They were predominantly located on internal walls & as shown in Figure 1 were in good condition. However those located on external walls were severely degraded. The example shown in Figure 2 is on a west facing wall & clearly offers no protection against rainwater ingress.

Failure Diagnosis

It was agreed that the failure was caused by photo-oxidative degradation of an orange pigmented PVC shroud after 30 years of natural weathering.

Lessons & Consequences


Figure 2 A PVC shroud after 30 years service involving direct exposure to sunlight
  1. The owners admitted that poor maintenance was responsible for the failure because the poor condition of externally sited shrouds would have been clearly evident many years before the failure.
  2. The condition of the shrouds after 30 years exposure to a temperate climate would suggest that they were not intended for external use.
  3. Carbon black filled EPDM or polyolefin thermoplastic elastomers would be the modern choice for the application.



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