The young woman, who was working for J-TEP Electrical & Plumbing, was taken to the Canberra Hospital after she received the shock while working at the Aurora apartment site on the Kingston foreshore.

Work Safety Commissioner Mark McCabe said early investigations suggested the fourth-year apprentice was working alone on a platform ladder and was shocked by a live circuit that she believed had been switched off.

"It's supposed to be turned off and when it is, it should be tagged so that no one else turns it back on,'' Mr McCabe said. ''She believed it had been turned off, but it had been turned back on.

"We will probably be issuing notices on the employer.

''There's a couple of things we're investigating, mainly some of the work practices involved and how the power, or how the electrical circuit, came to be live.''

The incident follows a spate of workplace accidents and deaths in the territory over the past year and an ACT government inquiry into safety practices in the construction industry.

The building union, the CFMEU, said on Thursday that it could take ''stern action'' over the latest accident.

''The CFMEU is extremely concerned about the reports coming from that building site,'' branch secretary Dean Hall said.

''This is very distressing. She's very lucky to be alive.

''Every worker around the territory should be concerned about someone allegedly turning electrical wires back on when they should have been off.''

Mr Hall said electrocution was one of the major causes of death on construction sites.

The government's inquiry into health and safety laws on ACT building sites found the ACT had the worst record for construction site safety in Australia with one in every 40 workers expected to sustain a serious injury on the job each year.

The territory's rate of serious injury was nearly double the national average.