When the developer of a new logistics park north of Watford was given a four-day shutdown window by the DNO to bring 33kV power onto the site, the ICP responsible called us in to handle the pulling and jointing element. The site sat off a Hertfordshire A-road, with the connecting switchgear inside a live primary substation half a mile away.
Three drum lengths of 240mm² triplex 33kV XLPE had to be pulled through pre-laid duct, with two straight joints and one termination at the new packaged substation. Tight bend radii on the substation approach, plus a 90° change of direction at the road crossing, made tension control critical.
What the job involved
- Pre-pull duct rodding and mandrel test on all three duct runs (approx. 600m total).
- Three drum-to-drum pulls of 240mm² 33kV XLPE triplex, tension-monitored with live data logging.
- Two straight joints in pre-cast pit boxes at the road crossing and field boundary.
- Outdoor termination at the new 33/11kV packaged substation, plus indoor terminations at the existing primary.
- VLF and partial discharge testing handed over to the DNO at end of works.
Key challenges
- Substation access window of just 14 hours per day, restricting jointing pit lighting setup.
- One run had a flooded pit that needed pumping out and damming before jointing could start.
- Drum positioning had to thread around an existing 11kV overhead line — no crane swings within the exclusion zone.
Outcome
- Pulls completed within calculated tension envelope (max recorded 8.2kN against a 12kN design max).
- All three joints passed VLF and PD testing first time.
- Site handed back to the DNO half a day inside the shutdown window — letting the ICP complete commissioning early.
Tight window, live site, and they didn't miss a beat. The pull data logs and joint records landed in my inbox before we'd even cleared the site.
— ICP Project Manager, Watford, Hertfordshire
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