Mr McCabe said a worker on an inner-north commercial site dropped a length of metal tubing from scaffolding and pierced a high voltage electricity cable last Friday.

About 600 electricity users lost power as a result of the incident and the tubing narrowly missed hitting a gas line exposed in the same trench.

Workers on the site possibly compromised a WorkSafe ACT investigation into the incident by continuing to remove the scaffolding, resulting in the issuing of official notices by inspectors.

Also last week, poor-quality scaffolding meant work was stopped at a home construction site in Crace, which was also found to have insufficient signage, large amounts of debris on footpaths and no amenities for workers.

Mr McCabe said the home owner thanked inspectors and said the builder had not responded to requests to clean up the site.

In the third incident last week, a worker on another commercial site in a development area fell through scaffolding more than three metres above ground.

The man's fall was broken and he did not suffer any serious injuries but was taken to hospital as a precaution and WorkSafe will consider revoking his employer's licence.

Fines will be considered and prohibition notices were issued.

''High-risk work, such as tasks involving working at height, or with or near electricity, are amongst the most dangerous activities on construction sites,'' Mr McCabe said. ''Companies and their site supervisors should be exercising the highest levels of vigilance when this type of work is being carried out.''

He called on construction companies ''to lift their game.''

WorkSafe ACT is working to provide more extensive guidance to site managers and construction companies about working safely at heights and Mr McCabe said the organisation would pursue ''whatever enforcement action it considers appropriate''.

''On [these] occasions, no one received serious injuries,'' he said.

''But they were lucky. The safety of our workers should never be left to luck.''