CENELEC / IEC Safety Earth

Single channel and star connected A.C. safety barriers must be connected to a high integrity earth by at least one and preferably two copper cables, each of cross sectional area of 4mm² or greater. The connection must be such that the impedance from the connection point to the main power system earth is less than one ohm. Intrinsically safe circuits in the hazardous area should be insulated from earth and must be capable of withstanding a 500V RMS A.C. test voltage for at least one minute. When using armoured or copper sheathed cables, the armour or sheath is normally isolated from the safe area busbar. Conformity with European Standards. IEC marking omits this character Explosion Protection symbol Table 2 Type of Protection Codes Table 3 Temperature Classification

E Ex ia IIC T4

Temperature Class Maximum Referred to Surface

Wiring and Cable Types

It is not permitted to connect more than one barrier circuit in the hazardous area to any other circuit. Both separate and twin cables may be used. A pair contained in a type ‘A’ or ‘B’ multicore cable (as defined in clause 5.3 of EN50 039) May also be used, provided that the peak voltage of any circuit contained within the multicore does not exceed 60V. The capacitance and either inductance or the inductance to resistance (L/R) ratio of the hazardous area cable must not exceed the parameters specified in Table 6. The reason for this is that energy can stored in a cable and it is necessary to use cable in which energy stored is insufficient to ignite an explosive atmosphere. To calculate the total capacitance or inductance for the length of cable in the hazardous area, refer to Table 7, which gives typical per kilometre capacitance and inductance for commonly used cables. Note: The flame detectors have zero equivalent inductance (L ambient of Temperature -20°C to +40°C T6 85°C Type of Equipment T5 100°C Code Protection Code Category T4 135°C ia Intrinsic safety 1 T3 200°C
i = 0) and a 0.03 F capacitance (C
i = 0.03 F). ib Intrinsic safety 2 T2 300°C d Flameproof 2 T1 450°C Gas group IIA IIB IIC These Flame Detectors are approved ia. Detectors approved to T4 at 40°C Capacitance F Inductance mH L/R ratio H/ohm 2.15 33.6 440 0.65 12.6 165 0.083 4.2 55 Table 6 28V Barrier, Maximum Permissible Stored Energy in Cables Table 7 Examples of electrical characteristics of cables commonly used in fire protection systems. Table 4 Subdivisions of Group II Gases Gas Group Representative Gas Other Gases, Liquids, Vapours
Cable Type Core Size mm² Conductor resistance ohm/km/core Inductance mH/km Capacitance µF/km 2 2 all all 1.5 1.5 1.5 1.5 12.1 12.1 12.1 12.1 0.534 0.643 0.77 0.19 0.13 0.08 0.09 0.21 0.17 0.15 2.77 1.58
Sheath IIC Hydrogen Acetylene, Carbon Disulphide
Resistance ohm/km core core to core to sheath IIB Ethylene Diethyl ether, Tetrafluoroethylene IIA Methane Butane, Methanol, Petroleum, Propane, Styrene MICC Pyrtenax light duty MICC Pyrotenex heavy duty Pirelli FP200 PVC sheathed and Insulated to BS6004 These Flame Detectors are approved IIC for listed gases in EN 50014. 4 9