An electricity substation that powers Nottingham's main hospital, the Queen's Medical Centre, has been broken into and vandalised by thieves.
Staff discovered that copper wiring had been stolen on Saturday afternoon.
Central Networks, which maintains substations, managed to re-route the power. It said the thieves put their lives and those of others in danger.
The trust, which runs the hospital, said it had back-up generators and no patients were at risk.
So far this year two people have died and two others have been seriously injured attempting to steal copper wiring from Central Networks' substations.