Technical Documentation: Fire Detectors used in hazardous areas
P-DET/EX/RCE/PM5/GKa/110995 14 Autronica Fire and Security AS
1.8 Potential equalizations: PE on ships.
A: Insulated sensor on non conducting wall:
PE-conductor only passing through.
B: Insulated sensor on conducting wall:
PE-conductor only passing through.
C: Metal sensor on conducting wall:
PE-conductor connected to inside of box. Outside earth screw
connected to wall.
D: Metal sensor on non conducting wall:
PE-conductor connected to box.
For an intrinsically safe circuit the main demands are:
1: Voltage, current and energy has to be below certain values (depending on
gas types), so that any sparks due to shortening or breaking the circuit do
not ignite the gas mixture.
This may be achieved by the use of a Zener barrier and restrictions for
inductively and capacity.
2: To avoid sparks between the IS circuit and the surrounding the use of a
Potential Equalization is necessary.
Normally this is done by a PE-conductor, grounded at the zener barrier.
When disconnected it shall withstand 500 V to ground. In welded steel
ships however, according to "Det Norske Veritas", the hull itself may be
used as potential equalization conductor.
3: The temperature of any component in an IS-circuit shall be below a given
value, depending on the gas group.
PE
+
-
+
PE
-
Zenerbarrier A B C D
Conducting wall etc.
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