34 900 Series V5.0: Installation Guide, April 1999
4.4. Fire monitors
4.4.1. Installation
It is important that the Series 970 Intrinsically Safe monitors are installed in such a way
that all terminals and connections are protected to at least IP20 when the detector is in
the base. You must take special care must with the rear of the mounting base where live
metal parts (rivets) might be accessible. The required degree of protection is obtained by
flush mounting the base on a flat surface.
If the base is mounted on a conduit box (e.g. BESA box or similar) whose diameter is less
than 85 mm, the base must be fitted with a back plate. The use of the back plate prevents
access to the metal parts and also protects the rear of the base from water ingress. A
conduit box, available from Aritech, can also be used to mount Intrinsically Safe bases.
Note that the earth terminal in the base is provided for convenience where continuity of a
cable sheaths or similar is required. It is not necessary for the correct operation of the
monitor nor is it provided as a termination point for safety earth.
4.4.2. Mounting bases
The base for the intrinsically safe range is not identical to that for the standard range.
This ensures that standard monitors cannot inadvertently be fitted to an intrinsically safe
system. For full details of the Series 950 address mechanism refer to section 3.2 Fire
monitoring controllers.
It has three double terminals and one single terminal:
L1: Line in and out, double terminal (‘+‘)
L2: Line in and out, double terminal (‘-’)
+R: Remote indicator (LED) positive supply, double terminal
Single terminal: An isolated terminal intended as a through connection point for
cable shields or for an earth connection.
It is absolutely necessary to observe polarity on terminals L1and L2. L1 must
always be kept positive. All intrinsically safe fire monitors are polarity sensitive.
The standard mounting base is designed so that a fire monitor fits in one way only,
without snagging, using a clockwise motion with no insertion force.
All mounting bases have a locking feature whereby a socket screw on each fire monitor
can be turned to locate into a fixing hole in the mounting base. This prevents the
unauthorised removal of a fire monitor.
When installing fire monitors in confined spaces, 110 mm from the surface must be
allowed for fitting and removal. Refer to Figure 26 “Schematic wiring diagram of
Intrinsically Safe zone.
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