Hundreds of premises in West Oxford including businesses on an industrial estate suffered a power cut after a contractor drilled through a cable.
Electricity supplies to a number of firms in Osney Mead were affected by the cut in supply which lasted a few seconds about 1.30pm.
Sharon Miller-McKenzie, a spokesman for Southern Electric, confirmed the company suffered a high-voltage fault in the area.
She added: "Unfortunately a contractor carrying out drainage work hit one of cables in Osney Mead and that caused a power cut affecting 840 customers.
"A network alarm sounded and we were able to re-route electricity for about 320 premises within 20 minutes.
"Another 200 were back on in 36 minutes, with the remaining premises back on by 2.15pm.
"We urge anyone who is going to be digging to get in touch with us to find out where our cables are laid."
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