Electrical Ratings; Special Conditions - MEDC BGE Manuel Technique

signifies suitability for use in the presence of gas.

6.0 ELECTRICAL RATINGS

(a) For versions which are equipped with up to two microswitches only – the maximum values for each switch
fitted are as specified in Table 1;
TABLE 1
Voltage Resistive Load Inductive Load
(d.c.) (Amps)
30 5
50 1
75 0.75
125 0.5
250 0.25
Voltage Resistive Load Inductive Load
(a.c.) (Amps)
125 5
250 5
(b) For versions which are equipped with the encapsulated housing – the maximum system values are 24V and
0.05A or 6V and 0.2A independent of the number of units connected in the system.

7.0 SPECIAL CONDITIONS

1) The units must not be incorporated in systems which limit the electrical supply ratings to the values above.
2) The wiring loom between the fixed and detachable enclosure shells must be located, during assembly, such
that the conductors and the restraint loop are not trapped in the sealing face between shells.
8 8 .0 Functional Safety
T
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 BGE 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 BGE 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.
Assessment of Functional Safety
The BG Call Point is intended for use in a safety system conforming to the requirements of IEC61508.
Sira Test & certification Ltd has conducted a Failure Modes Effect and Diagnostic Analysis (FMEDA) of
the BG Break Glass unit against the requirements of IEC61508-2 using a proof test interval of 8760hrs.
S
The Call Point is classed as a Type A device.
© Cooper MEDC 2011
All manuals and user guides at all-guides.com
(Amps)
3
1
0.75
0.03
0.03
(Amps)
5
5
01/12