The work, which started recently, continues a refurbishment scheme that commenced last summer with planned completion in October 2014.
National Grid project manager Graham Livings said: "This major investment by National Grid will provide modern high-capacity cables which will help ensure people continue to enjoy safe and reliable electricity supplies in the future.
"We’re keen to minimise disruption for road users wherever possible and are working closely with Essex County Council as we plan and deliver the project."
National Grid said the replacement of the lines will not have an impact on the local power supply, as the flow of electricity will be re-routed through other lines.
