An ageing single-storey substation feeding a residential estate in Enfield was being retired and replaced by a new GRP packaged unit on the same footprint. Before demolition could begin, six cables — a mix of LV services and an 11kV ring — needed to be safely isolated, spiked, and cut to allow the old switchgear to come out.
The DNO appointed us to deliver the spiking element on the back of our existing framework competency. Two-week notice, two-day on-site window.
What the job involved
- Liaison with the DNO control room for sanction-to-test on each cable in turn.
- Positive ID against substation records and route tracing for two cables that had been altered since the original drawings.
- Remote-fired hydraulic spike gun setup with full exclusion zone on each cable.
- Photo records and timestamped sign-off for every spike.
- Cable cuts and capping handed back to the demolition contractor at end of works.
Key challenges
- One cable's drawing record didn't match the physical route — we re-traced and re-identified before spiking.
- Resident access through the substation compound had to be maintained during set-up days.
- Cold-weather working — the sub was unheated and jointing pits frosted over each morning.
Outcome
- All six spikes carried out without incident, inside the two-day window.
- Records issued to the DNO same-day, allowing demolition to mobilise on the Monday.
- Subsequent commissioning of the new packaged sub completed on the DNO's original programme.
We threw a curveball at them with that mis-identified cable and they re-traced it on site rather than blindly spiking. That's the difference between a competent contractor and one who's just turning up.
— DNO Cable Engineer, Enfield, North London
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