The contract, the largest offshore cable installation by OMM to date, was completed this week using the 122-metre cable vessel Deep Cygnus.
OMM was originally contracted to install 29 connections.
Greater Gabbard will consist of 140 Siemens turbines when completed. Over 100 of these have been installed.
The wind farm, owned and operated by SSE and RWE Npower, is located 25 kilometres off the coast of eastern England and should be fully operational in 2012.
However, the developers have admitted there was a possibility it could overrun following a row with Fluor.
Greater Gabbard Offshore Winds Limited (GGOWL), which is jointly owned by Scottish & Southern Energy (SSE) and RWE, was hit by a £300 million claim earlier this year from Fluor.