MEDC BG - Manual (Page 7)

© MEDC 2013 11/13
6.0 ELECTRICAL RATINGS
For versions which are equipped with up to two microswitches only, the maximum values for each
switch fitted are specified in the table below:
For versions which are equipped with the encapsulated housing, see the values stated on the
certification label for reference.
7.0 SPECIAL CONDITIONS
1. The units must be incorporated in systems which limit the electrical supply ratings to the values
above
2. The wiring loom between the fixed and detatchable enclosure shells must be located, during
assembly, such that the conductors and the restraint loop are not trapped in the sealing face
between shells
3. The encapsulated LED and encapsulated resistor/diode units shall be protected by fuses rated for a
prospective short circuit current of at least 1500A
8.0 FUNCTIONAL SAFETY (BGE Only)
Introduction
The BG Call Point has been designed for use in potentially explosive atmospheres and harsh
environmental conditions. The glass reinforced polyester enclosures are suitable for use offshore or
onshore, where light weight combined with corrosion resistance is required.
The function of the BG is to raise an alarm manually once verification of a fire or emergency condition
exists, by breaking the Glass.
The BG Break glass Unit is configured with either a single series Resistor (R1) or an R1 and end of line resistor
known as R2. No Current passes through R1 in either configuration until the glass has been broken and the
switch contacts have closed. Upon closure of the switch the current is then sent through R1 and hence changes
the resistive value in the circuit which triggers the alarm. The R2 resistor always has a current flowing through
which provides the reference resistive value for the circuit. The circuit can diagnose an open circuit failure in
R1 without having to trigger the system via a continuity check which is a form of diagnostics for determining if
an R1 resistor has failed Open Circuit. This form of diagnostics does however require a proof test to be
conducted in order to identify the failure and depending on the set up of the system the defective Resistor may
not be easily traceable if there are several BG break glass Units in the system. The end of line resistor R2 is
used for the purpose of detecting an open or short circuit in the supply conductors.
The safety function of the Call Point is to raise the alarm when the Glass is Broken
Under No fault (Normal) Operating conditions the BG Break Glass Unit will raise the alarm upon
operating the switch via breaking the glass.
Under fault conditions the failure mode of the Break Glass is a failure to raise the alarm. For the failure
rate associated with this failure mode please refer to the table below.
Voltage (d.c.) Resistive load (A) Inductive load (A)
30 5 3
50 1 1
75 0.75 0.75
125 0.5 0.03
250 0.25 0.03
Voltage (a.c.) Resistive load (A) Inductive load (A)
125 5 5
250 5 5