Dynamic elaboration on the Art & Science of Hazardous Area Protection
In fact the Ex Labels/ Tags or the Markings on the Electrical components , manufactured for use in the Hazardous areas are “Regional Language Free”.
A system of symbols & alpha-numeric characters is used to fully describe the characteristics and operational parameters of the relevant electrical component.
Let us see the following label of a Junction Box
The LABEL or the MARKING should be clearly visible on a main part or the exterior of the equipment, prior to the installation and should remain visible after the installation.
Let us check the marking for the following points:
The Ex Marking
( G stands for the Gas & M stands for the below-surface or MINES with firedamp)
– I for electrical equipment for mines susceptible to firedamp;
– IIA or IIB or IIC for electrical equipment for places with an explosive gas atmosphere other than mines susceptible to firedamp.
When the electrical equipment is for use only in a particular gas, the chemical formula or the name of the gas in given in parentheses.
When the electrical equipment is for use in a particular gas in addition to being suitable for use in a specific group of electrical equipment, the chemical formula shall follow the group and be separated with the symbol “+”, for example, “IIB + H2”.
[GAS Group IIB + H2:- It simply means that the equipment is safe for use in GAS Group IIB and additionally, it is also and only safe in Hydrogen filled areas. Hydrogen itself belongs to GAS GROUP IIC. (IEC 60079-0- edition 6)
(NOTE 1 Equipment marked “IIB” is suitable for applications requiring Group IIA equipment.
Similarly, equipment marked “IIC” is suitable for applications requiring Group IIA and Group IIB equipment.)
Table 3 – Relationship between gas/vapors or dust subdivision and equipment groups
NOTE : Equipment group II can be used with all GAS GROUPS
Ga or Gb or Gc or Ma or Mb
f. Ambient Temperature for the operation . (Electrical equipment designed for use in normal temperature range of -20°C to +40ºC does not require marking of the Ambient Temperature range . Equipments designed for use in other than this range is considered special . In this case the marking or the label will have the symbol Ta or T amb. together with both the upper & lower ambient temperatures or if this is not possible due to small space of the label then symbol X wiil be used to indicate special conditions of use.)
Marking ( As per updated IEC documents )
Same first 5 rules,as that for the Explosive Gas Atmosphere, apply for the Explosive Dust Atmosphere (EDA). The difference is the Protection Type , as in the following detail:-
(Ref: IEC 60079-0)
IIIA IIIB IIIC
For Group III Equipments. The complete information about the Multiple Maximum Temperatures ( with dust layer etc.)
should be included in the certificate.
Last But not least
Do study the relevant Ex Certificate.
(For Associated Apparatus see the post Associated Apparatus)