in some and the rock in others. At the centre of the tunnel is a large chamber where pumps were located to remove water. Running the length on one side are cement racks to hold the high tension wires to supply electric power for trams and trains on the north side of the harbour. The tunnel held twelve cables, 8 x 11,000 volt and two 50 pair communication cables. At one end was a pool some six feet in depth, to collect soakage, and be pumped to the surface. The tunnel is perfectly straight, except at Greenwich Point, where it takes a bend to allow an outlet. From outlet to outlet it measures 1,760 feet. At each shaft it descends steeply into the ground at a grade of 2 in 1, except in a section at the Greenwich end; where a steep cut had to be made - there the grade is 1 in 1.3. No evidence remains above ground at the Birchgrove entry point, but the shaft and tunnel structure (and early cabling) remain below ground as evidence of significant infrastructure designed and constructed by State Rail. Heritage listing The tunnel was a major technological and engineering achievement and was the first such venture to be undertaken in Australia without overseas assistance. It was a major link in the power supply to the railway and tramway system between Sydney and the North Shore and although flooded is an important element of the development of public transport in Sydney. Sydney Harbour railway electricity tunnel was listed on the New South Wales State Heritage Register on 2 April 1999. See also References Attribution New South Wales State Heritage Register Birchgrove, New South Wales Electric power infrastructure in New South Wales Articles incorporating text from the New South Wales State Heritage Register Tunnels in Sydney