Hi, thank you for your product enquiry.
This British General 20A Flex Outlet Plate White is for use in connecting a cable into a suitably protected mains circuit, so if your extension cable is only rated for 13A then you would need a 13A fuse in the supply somewhere (usually in the form of a fused connection unit) in order to prevent overloads causing damage to the cable.
Answered by: Nexus Technical Team
Date published: 2019-08-02