wrote:

Best practice is to tap off local lighting circuit as if on dedicated
circuit [which AC only
alarms have to be] is a chance that if alarms play up, householder may
switch off that circuit breaker.
If lighting is off they'd pretty soon notice.

If the alarms are being fitted under requirement of building regs (say
because they are required as a result of the addition of a third storey
to the building - i.e. loft conversion), then they must be on their own
circuit, and they must also have a battery backup (which means you can't
simply flip a breaker to turn them off anyway).

In a normal domestic two storey house, you can get away with using a
lighting circuit for power, although this can also introduce a risk if
you have separate lighting circuits for both up and downstairs, since
your fire alarms would then need to be powered from only one circuit or
the other (not both) to gurantee they work in unison, and also do not
bridge the two circuits.

--
Cheers,

John.

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