The £17 million facility is being built to secure existing supplies to 13,000 customers and meet future demand to the north and west of St Helier.
The work began in January and contractors Jayen have now started piling to support the floor slab.
Work on the new retaining wall to protect the facility will begin in the next few weeks.
Once this work is completed, French specialists INEO will build the actual sub-station.
See more pictures in Wednesday’s JEP.
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