Many Ex equipment items combine multiple protection concepts in one certified assembly. This unit covers how to read combined markings, the Ex de motor arrangement, which inspection standards apply to each protection element, and cost-effectiveness guidance for Zone 1 and Zone 2.
Learning Objectives
Read a combined Ex marking and identify each protection element
Explain the Ex de motor — what is Ex d and what is Ex e
State which inspection standards apply to each element of a hybrid assembly
Identify which element of an Ex de motor requires a barrier gland
Describe protection method selection guidance for Zone 1 and Zone 2
Hybrid Protection Concept
Combined protection uses multiple Ex types in one assembly — taking the best features of each. IEC 60079-0 requires protection symbols in alphabetical order: first symbol = primary protection, subsequent = secondary.
Common Hybrid Markings
Ex de — Ex d terminal box + Ex e motor windings Ex ed — Ex e enclosure + Ex d component inside Ex edq — Ex e enclosure + Ex d lamp + Ex q ballast Ex d [ia Ga] IIC Gb — Ex d enclosure containing IS associated apparatus
Ex de Motor
Ex de Motor
Terminal box: Ex d (flameproof) — can survive internal explosion. Motor windings: Ex e (increased safety) — no flamepath, prevents arcing and excessive temperatures. Both tE time (Ex e) and flamepath condition (Ex d) must be inspected. BARRIER gland required for SWA cable into the terminal box. External earth tag mandatory. Both IEC 60079-1 AND IEC 60079-7 apply.
Which Standard Applies?
For hybrid equipment, BOTH relevant standards apply to their respective elements simultaneously. A missing bolt on an Ex de terminal box cover is Category X under IEC 60079-1 — regardless of the Ex e winding condition. The tE relay setting failure is Category A under IEC 60079-7 — regardless of the flamepath condition.
Reading Hybrid Markings
Marking
Primary
Secondary
Ex de
Ex d terminal box
Ex e windings
Ex ed
Ex e enclosure
Ex d component
Ex edq
Ex e enclosure
Ex d lamp + Ex q ballast
Selection Guidance
Zone 1: Ex e first (lighter, cheaper, easier maintenance); Ex de for motors; Ex d when sparking components need containment; Ex i for instrumentation.
Zone 2: Maximise Ex e and Ex n; minimise Ex d. Ex nR lighting often more economical than Ex d in Zone 2.
Quick Check — 5 Questions
Test key concepts from this unit before moving on.
Q1Summary
An Ex de motor has a missing bolt on the terminal box cover. What category and which standard?
Both standards apply to their respective elements. A missing terminal box bolt means the flamepath may not be clamped — Category X under IEC 60079-1. Both elements must pass their respective criteria independently.Ref: IEC 60079-1 / IEC 60079-7
Q2Summary
Why is a barrier gland required for SWA cable entering an Ex de motor terminal box?
The terminal box IS Ex d. A barrier gland inner seal sits within the flamepath zone and prevents hot gases being forced through cable armour during an internal explosion. This derives from the Ex d terminal box requirement.Ref: IEC 60079-14
Q3Summary
Equipment marked "Ex de IIC T4 Gb" in a Zone 1, IIB, T4 area. Is IIC marking a problem?
IIC covers IIA, IIB, and IIC. T4 meets T4. Gb is Zone 1 suitable. Compliant.Ref: IEC 60079-0
Q4Summary
"Ex ed" control station marking means which configuration?
Ex ed: Ex e (increased safety) is primary enclosure; Ex d (flameproof) is a component inside the Ex e enclosure — e.g. a small Ex d switch inside an increased safety control station.Ref: IEC 60079-0
Q5Summary
Detailed inspection of an Ex de motor — what two items relate to each protection element?
(1) Ex d terminal box: flamepath gap measurement with calibrated feeler gauges. (2) Ex e windings: verify overload relay trips within tE at motor stall current IA/IN ratio. Both are Detailed inspection.Ref: IEC 60079-1 / IEC 60079-7
EX Academy — independent CompEx-style preparation. Not official CompEx course materials.
Unit 9 · Ex01–Ex04 · Full Manual
Combined (Hybrid) Methods of Ex Protection
Many Ex equipment items combine multiple protection concepts in one certified assembly. This unit covers how to read combined markings, the Ex de motor arrangement, which inspection standards apply to each protection element, and cost-effectiveness guidance for Zone 1 and Zone 2.
Learning Objectives
Read a combined Ex marking and identify each protection element
Explain the Ex de motor — what is Ex d and what is Ex e
State which inspection standards apply to each element of a hybrid assembly
Identify which element of an Ex de motor requires a barrier gland
Describe protection method selection guidance for Zone 1 and Zone 2
9.2 Combined Methods of Ex Protection
Hybrid protection combines two or more Ex types in one certified assembly — using the best features of each for economic and practical benefit.
IEC 60079-0:2011 clause 29.6 requires protection symbols in alphabetical order. First symbol = primary protection; subsequent symbols = secondary, applied to specific components.
Common Hybrid Markings
Ex de — Ex d terminal box (flameproof) + Ex e motor windings (increased safety). Most common on motors. Ex ed — Ex e enclosure + Ex d component (e.g. switch) inside. Ex edq — Ex e enclosure + Ex d lamp mechanism + Ex q powder-filled ballast. Common in luminaires. Ex d [ia Ga] IIC Gb — Ex d enclosure (Gb) containing IS associated apparatus with ia Ga output.
9.4 Ex de Motors
Ex d — Flameproof Terminal Box
The terminal box can withstand and contain an internal explosion. Cable entry requires a certified Ex d BARRIER gland for SWA armoured cable — the inner body seal protects the flamepath at the cable entry. The terminal box is Ex d regardless of the motor windings being Ex e.
Ex e — Increased Safety Motor Windings
No flamepath in the winding chamber. Designed to prevent arcing, sparking, and excessive surface temperatures. The tE time (marked on nameplate) is the maximum time the overload relay must trip within at locked-rotor current. The overload relay must be verified during Detailed inspection.
Element
Standard
Key Inspection Items
Terminal box
IEC 60079-1 (Ex d)
All bolts present and torqued; flamepath free of sealant/corrosion; barrier gland correct type and tight; flamepath gap within tolerance (Detailed)
Motor windings
IEC 60079-7 (Ex e)
Overload relay setting vs tE time (Detailed); nameplate legible; T-class correct; external earth tag fitted
Both
IEC 60079-17
Zone, gas group, T-class, ambient; IP intact; dataplate legible
9.5 Protection Method Selection Guidance
Zone
Preference
Notes
Zone 1
Ex e first; Ex de for motors; Ex d when Ex e not practical; Ex i for instrumentation
Ex e is generally lighter, cheaper, easier to maintain. Ex d only where sparking components need containment.
Zone 2
Maximise Ex e and Ex n; minimise Ex d
Ex nR for lighting often more economical than Ex d. Ex nA for general Zone 2 equipment.
Unit 9 Knowledge Check — 10 Questions
CompEx-style questions covering the full unit content.
Q1Unit {num}
An Ex de motor tE time is 12 seconds. Overload relay is set to trip at 18 seconds. Is this compliant?
The relay must trip within tE = 12 seconds at motor stall current. 18 seconds exceeds tE — the windings will heat beyond T-class limiting temperature. Category A.Ref: IEC 60079-7
Q2Unit {num}
IEC 60079-0 requires protection symbols in what order?
IEC 60079-0 requires alphabetical order. So Ex de (d before e), Ex edq (e, d, q), etc.Ref: IEC 60079-0:2011 clause 29.6
Q3Unit {num}
For Ex de motors, which earth paths are required by IEC 60079-14?
Two separate earth paths required: (1) cable armour earthed through gland armour clamp to terminal box body; (2) external earth conductor from motor body stud directly to site earth bar. Neither alone is sufficient.Ref: IEC 60079-14
Q4Unit {num}
What inspection grade measures the flamepath gap of an Ex de motor terminal box?
Flamepath gap measurement requires the cover removed and calibrated feeler gauges applied — Detailed inspection, with equipment de-energised.Ref: IEC 60079-1 / IEC 60079-17
Q5Unit {num}
An Ex edq luminaire has powder filling partially missing from the ballast. What category?
Missing powder filling in the ballast unit means the Ex q protection concept is compromised. Category A — replace the ballast with a certified replacement. Also inspect the Ex e enclosure and Ex d lamp mechanism independently.Ref: IEC 60079-5 / IEC 60079-17
Q6Unit {num}
Equipment marked "Ex nA d IIC T4 Gc" — what does the "d" signify?
Ex nA d: non-sparking (nA) primary enclosure for Zone 2, with specific Ex d sub-enclosure protecting internal sparking contacts.Ref: IEC 60079 — Hybrid Zone 2
Q7Unit {num}
An Ex ed control station is found in a Zone 1, IIB, T4 area. The Ex e enclosure is marked IIB and the Ex d switch inside is marked IIA. What is the finding?
Every protection element must be rated for the area gas group independently. The Ex d switch (IIA) does not cover IIB gases — its flamepath dimensions are too wide for ethylene or H₂S. Category X deficiency. Both the enclosure and internal components must be separately rated for the area gas group.Ref: IEC 60079-0 — Gas Group Selection
Q8Unit {num}
Why must the overload relay trip within tE for an Ex e motor?
If the relay fails to trip within tE, the motor windings heat past the T-class limiting temperature. The motor surface temperature then exceeds the marked T-rating — the motor becomes an ignition source in the hazardous area. This is why tE relay verification is safety-critical and a Detailed inspection requirement at commissioning.Ref: IEC 60079-7
Q9Unit {num}
An Ex de motor nameplate shows tE = 8s, IA/IN = 6.2. The MCC overload relay is Class 10 (10 second trip). Is this compliant?
Relay thermal class designations are generic. For Ex e compliance, the relay must be verified to trip within tE at the specific IA/IN ratio. The relay must be set (and tested) to trip within 8 seconds when carrying 6.2× full-load current from maximum operating temperature. Class 10 does not automatically guarantee this.Ref: IEC 60079-7 / CVT
Q10Unit {num}
An Ex d [ia Ga] IIC Gb equipment marking — what can connect to the IS output terminals?
The IS output must be used with Ex ia IIC certified field devices whose entity parameters (Ui, Ii, Pi, Ci, Li) are compatible with the associated apparatus output (Uo, Io, Po, Co, Lo). The IIC gas group applies to both the outer enclosure and the IS circuit — both must be IIC rated.Ref: IEC 60079-11