Ex Equipment Selection — Step by Step Decision Guide

Ex equipment selection is a systematic process — each decision builds on the previous one. Follow these steps in order and you will always arrive at the correct specification for any hazardous area installation.

Step 1 — Confirm the Zone Classification

Before selecting any equipment, verify the zone classification for the installation location from the official area classification drawing. Zone determines the minimum EPL required:

• Zone 0 → EPL Ga minimum
• Zone 1 → EPL Gb minimum
• Zone 2 → EPL Gc minimum (or higher)
• Zone 20 → EPL Da minimum
• Zone 21 → EPL Db minimum
• Zone 22 → EPL Dc minimum (or higher)

Step 2 — Identify the Gas Group

Check the area classification drawing or site DSEAR assessment for the gas group. Equipment must be rated for the gas group present or a higher group:

• IIA area → IIA, IIB, or IIC equipment acceptable
• IIB area → IIB or IIC equipment only
• IIC area → IIC equipment only — no exceptions

Step 3 — Determine the Temperature Class

Identify the auto-ignition temperature (AIT) of the flammable substance present. The equipment T-class maximum surface temperature must be less than the AIT:

• AIT >450°C → any T-class acceptable
• AIT 300–450°C → T2 or lower (T1)
• AIT 200–300°C → T3 or lower
• AIT 135–200°C → T4 or lower
• AIT 100–135°C → T5 or lower
• AIT 85–100°C → T6 only

Step 4 — Select the Protection Type

Choose the appropriate protection type for the equipment function and environment. Ex d (flameproof) is most common for Zone 1 process plant equipment. Ex e (increased safety) is used for terminal boxes, luminaires, and motor bodies. Ex i (intrinsic safety) is used for instrumentation.

Step 5 — Specify Cable Glands and Accessories

For Ex d enclosures: identify entry type (threaded or clearance), check volume, specify barrier or non-barrier accordingly. For Ex e enclosures: specify non-barrier glands with nylon IP washers for threaded entries, or with IP washer + serrated washer + locknut for clearance entries. Consider enclosure body material for earthing requirements.

Step 6 — Verify the Certificate

Once equipment is specified, verify the ATEX or IECEx certificate: gas group on certificate must match or exceed area gas group; EPL must be appropriate for zone; T-class must not exceed AIT; no special conditions of use that affect the installation.