How to read an Ex marking before you order
II 2G Ex db IIC T4 Gb — what each field constrains, and why the certificate rather than the catalogue is the governing document.
An equipment marking is a compact specification. Read left to right, it states the equipment group and category, the atmosphere, the type of protection, the explosion group, the temperature class and the equipment protection level.
'II 2G' places the equipment in Group II (surface industry), category 2, for gas. Category 2 corresponds to Zone 1. 'Ex db' identifies flameproof protection. 'IIC' is the explosion group — a IIC machine may be used where IIA or IIB is required, but not the reverse.
'T4' is the temperature class, meaning maximum surface temperature does not exceed 135 °C. This must sit below the ignition temperature of the gas actually present. 'Gb' is the equipment protection level, which maps to the permitted zone.
The marking on the certificate governs. A catalogue description that summarises it — 'suitable for hazardous areas' — is not a substitute, and no supplier should ask you to rely on one.