It's deep red and blue glow makes it look almost futuristic yet its been part of the inner workings of the Durie Hill elevator since 1950.

The elevator's mercury arc rectifier is one of the few in the world to be used for public transport.

A mercury arc rectifier is a vacuumed glass bulb which contains liquid mercury and converts alternate electrical current to direct current.

When Whanganui's tramway closed in 1950 the elevator, which used DC electricity, was not compatible with the city's new AC electrical gird so a Hewittic 150/6 mercury rectifier was installed to keep the elevator operating.

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Whanganui & Partners digital and online lead Paul Kjoss says few mercury arc rectifiers are used for public transport.

"I didn't know we had one in Whanganui or realise how unique it is. It really is like something out of Doctor Who," he says.

The rectifier is the subject of recently installed signage at the elevator made up of three interpretive panels to explain how the underground elevator operates, including photographs of historical equipment the public never sees.

A mercury arc rectifier was also used to power the lift in the old building on the corner of Drews Ave an Taupo Quay which is now the Ucol Community Education Centre.

A Hewittic 150/6 mercury rectifier was installed in the Durie Hill elevator tower to convert the AC grid supply to DC electricity. Photo/Steve Caudwell
A Hewittic 150/6 mercury rectifier was installed in the Durie Hill elevator tower to convert the AC grid supply to DC electricity. Photo/Steve Caudwell