The company that contracted the man, Vause Wireline Ltd, was also sentenced and fined $30,000.
L&M Energy Ltd, which runs the site in partnership with NZEC Wiahapa, was not charged over the incident.
WorkSafe New Zealand chief inspector Keith Stewart said the incident would not have happened had the risk posed by the cellar been identified earlier.
The cellar has now been filled in.
"Both companies had a duty to identify and manage risks at the site before workers were put in harm's way. A proper assessment would have found that the clips were missing," Mr Stewart.
He said that a second way of securing the grating should also have been in place, as well as a safe escape route in case of falls.
"This incident could have been avoided with a bit more care and attention to risk identification. Once a hazard is identified it is often relatively simple to manage."
