I have to replace 4 night storage heaters adding a fifth but I only have a four way old wylex cu protected with a 63amp 30mA legrand rccb. I have to install 2 elnur 2.55kw heaters and 3 elnur 1.7kw heaters, is it safe to put 2 of the 1.7kw heaters into one 15amp rewireable fuse if they are both on seperate 2.5mm twin and earth radial circuits. Or is this going to require me to upgrade the cu to one with more ways. I worked out that both heaters would be pulling 14.78 amps but not sure if a 15amp rewireable would take that pull so close to its rating
For a 15A fuse 15A is the continuous rating so 14.8A is OK. As to re-wireable this is something which I have talked about with my father-in-law. He can have re-wireable fuses as he is classed as skilled but my daughter can't as she is not classed as skilled. It is really all down to understanding what happens if wrong wire is used and so ensuring wrong wire is never used.
So in your own house one could claim you are skilled. But you could not claim some one else is skilled if you are doing the work for them.
However although easy to change re-wireable to MCB before doing so you should check the loop impedance.
The way you talk it would seem your doing the work for some one else? Not sure where you are. In England from April there are new rules so now three different sets of rules. One for Scotland, One for England and one for the rest of UK. But the main thing as always is insurance.
Do remember 2.5 T&E does not have a fixed current rating it depends on the route.