Fire alarm supply

[Sintra]

thanks sintra for taking an interest and answering but without being pedantic over the page 537.3.2.1 it says devices for switching off for mechanical maitenance can be a number of things plug & socket, circuit breaker.I'm not advocating using a plug and socket.Also says the switch need not interupt neutral conductor.Not picking and grateful for help"its these ambiguous regs again"

You have got to love the regs.

The original post did state isolation not mechanical maintenance.