"Grade C: A system of fire detectors and alarm sounders (which may be combined in the form of
smoke alarms) connected to a common power supply, comprising the normal mains and a
standby supply, with central control equipment."
This sounds to me more like a PSU supplying the power to the heads, as opposed to a grade D system which has mains with internal battery back up.
However,I've just checked annex B which states -
"B.5.1 More effective control and monitoring of a fire detection and fire alarm system can be provided by
connecting all fire detectors to a common power supply, comprising the normal mains, rectified and
regulated as appropriate, with a standby supply, such as a secondary battery. Examples of such systems
include:
a) one or more smoke alarms and heat alarms operating at extra-low voltage and connected to a control
unit at an appropriate location in the dwelling;
b) intruder alarm systems or social alarm systems that incorporate control and indicating equipment to
which one or more fire detectors are connected; the detectors can be smoke alarms or fire detectors with
independent sounders.
B.5.2 This type of system normally incorporates a secondary battery of a type unsuitable for use in normal
domestic appliances and removable only with the use of a tool. The battery is, therefore, unlikely to be
removed for other purposes"
So, in reading this it's either a fire panel stuck in a meter cupboard somewhere (which explains a few things that I've came across) or an intruder panel (Arghhh!!!) with detection on it.
