I need to install a second switch fuse for a separate supply to an extension. Would prefer to use this model as they are small enough to fit onto existing board in a small cupboard where the supply enters the house (and leave room for the extra RCD that's now required) but concerned that they are plastic and Amendment 3 of 17th Edition regs says 'switchgear including consumer units' need to be of non combustible material. Can I use it or should I go for one of the bigger metal clad ones, replace the board and make the cupboard bigger - which is a whole lot more work?