Ex e protection prevents ignition by eliminating potential ignition sources through quality of construction — controlled temperatures, de-rated terminals, specified creepage distances, and secure conductor clamping. This unit covers terminals, the critical tE time for motors, cable gland selection, and inspection requirements.
Learning Objectives
Explain how Ex e prevents ignition and why sparking components are not permitted inside Ex e enclosures
Define creepage distance, clearance distance, and Comparative Tracking Index (CTI)
Explain tE time and state why the overload relay setting is a safety-critical function
State the cable gland accessories required for threaded and unthreaded entries in metallic and plastic enclosures
Identify inspection faults specific to Ex e equipment including terminal overloading and damaged IP seals
Protection Concept
Ex e prevents ignition by eliminating potential ignition sources — no arcs, sparks, or excessive temperatures, internally or externally. The letter "e" comes from the German Erhöhte Sicherheit (increased security). No flamepath. Not suitable for sparking components (switches, contactors, relays) — these must not be installed inside Ex e enclosures unless they have their own Ex d protection.
IEC 60079-7 Definition
A type of protection applied to electrical apparatus in which additional measures are taken to give increased security against the possibility of excessive temperatures and of the occurrence of arcs and sparks in normal service or under specified fault conditions. Specified fault conditions include foreseeable abnormal operation such as motor overload or lamp failure.
EPL Gb — Zone 1 and Zone 2. Certified for all Group II subdivisions (IIA, IIB, IIC). Ambient: -20°C to +40°C unless otherwise marked.
Terminals — Creepage, Clearance and De-rating
Ex e terminal boxes use component-certified terminals with increased creepage and clearance distances and locking devices to prevent conductor loosening.
Term
Definition
Clearance distance
Shortest distance through air between two conductors (flash distance)
Creepage distance
Shortest distance between conductors along the surface of an insulator (tracking distance)
CTI
Comparative Tracking Index — resistance of insulation material to surface tracking under test
Terminals are de-rated to approximately 50% of standard industrial current ratings to limit temperature rise. Example: a 4mm² terminal rated 36A standard is rated only 21A in Ex e service. The number of terminals fitted in any enclosure is limited by the manufacturer's certification to control temperature.
⚠ Terminal Overloading — Category A Deficiency
Exceeding the certified terminal count, using cables larger than certified, or using piggyback connectors reduces creepage distances and increases temperature — Category A deficiency. Replace the enclosure with a correctly sized one.
tE Time — Motor Protection
Increased safety motors contain no sparking components. The tE time (in seconds) is the maximum time the overload relay must trip within, from the point of motor stall, measured from maximum normal operating temperature.
tE Time
The time taken for the motor windings to reach the limiting (T-class) temperature from their maximum normal operating temperature, when carrying the starting current IA at maximum ambient temperature. The thermal overload relay must trip within this time under locked-rotor conditions. tE time and the starting current ratio IA/IN are marked on the motor nameplate.
⚠ Overload Relay Setting — Safety Critical
The overload relay trip time must be verified against tE during commissioning (Detailed inspection). A relay set to trip too slowly is a Category A deficiency. If the relay does not trip within tE, the motor windings reach the T-class maximum temperature and the surface temperature of the motor body could exceed the T-rating — potential ignition source.
Cable Gland Selection for Ex e
Ex e enclosures do not have a flamepath — the gland is needed only to maintain IP integrity and provide cable retention and armour earth continuity. Any certified Ex e gland is acceptable (barrier glands are acceptable but not required).
Enclosure/Entry Type
Required Accessories
Metal enclosure, threaded entry ≥6mm wall
Gland only (thread provides IP seal)
Metal enclosure, threaded entry <6mm wall
Gland + IP sealing washer
Metal enclosure, clearance hole (no thread), no gland plate
Gland + earth tag + IP washer outside + serrated washer + locknut inside
Plastic (non-conductive) enclosure, no internal earth plate
Gland + earth tag + IP washer outside + locknut inside
Inspection
All cover bolts fitted and tight
Unused entries sealed with certified Ex e blanking plugs
Cable gland accessories properly installed per entry type
Cover IP seal undamaged and correctly seated
No more than 1mm conductor exposed between core insulation and terminal
Only one conductor per terminal side (unless certification permits more)
Conductors secure — no loose connections
Terminals not overloaded — conductor count and size within certification
Overload relay setting verified against tE time (Detailed inspection)
T-class correct for area
Quick Check — 5 Questions
Test key concepts from this unit before moving on.
Q1Summary
What does tE time represent on an Ex e motor nameplate?
tE is the time in seconds for motor windings to reach the T-class limiting temperature from their maximum normal operating temperature when carrying locked-rotor current IA. The overload relay must trip within tE. An incorrectly set relay that trips too slowly is a Category A deficiency — the motor windings and surface could exceed the rated T-class temperature.Ref: IEC 60079-7 — tE Time Definition
Q2Summary
An Ex e terminal box is certified for 12 × 2.5mm² conductors. An engineer installs 16 cables. What is the deficiency category?
Exceeding the certified terminal count is Category A — it compromises creepage distances and increases temperature rise beyond tested values. The terminal box must be replaced with one correctly sized for 16 circuits. Piggyback connectors or other workarounds are not acceptable.Ref: IEC 60079-7 — Terminal Population Limits
Q3Summary
A metal Ex e junction box has a clearance-hole (unthreaded) cable entry. What accessories are required in addition to the gland?
For unthreaded (clearance hole) entries in metallic Ex e enclosures without a removable gland plate: IP sealing washer on the outside (between gland face and enclosure), serrated washer and locknut on the inside. The IP washer seals the interface; the serrated washer maintains earth continuity through any surface coating.Ref: IEC 60079-7 / IEC 60079-14 — Cable Gland Accessories
Q4Summary
Why must arcing components (switches, contactors) NOT be installed inside an Ex e enclosure?
Ex e protection works by ensuring that no arcs, sparks, or excessive temperatures occur in the enclosure in normal operation. Arcing components (switches, contactors, relays) defeat this by definition. They may only be installed in Ex e enclosures if they are themselves separately protected within Ex d sub-enclosures (hybrid Ex de arrangement).Ref: IEC 60079-7 — Ex e Protection Principle
Q5Summary
What is the Comparative Tracking Index (CTI) used to assess in Ex e equipment?
CTI (Comparative Tracking Index) is obtained from tests in which an electrolyte is dripped onto an insulating surface between electrodes with a voltage applied. It measures how resistant the insulation material is to tracking — surface current flow across contaminated insulation that leads to carbon deposit formation. Ex e terminal materials (Melamine, Polyamide, ceramic) are selected for high CTI performance.Ref: IEC 60079-7 — CTI Definition
EX Academy — independent CompEx-style preparation. Not official CompEx course materials.
Unit 4 · Ex01 & Ex02 · Full Manual
Increased Safety — Ex e
Ex e protection prevents ignition by eliminating potential ignition sources through quality of construction — controlled temperatures, de-rated terminals, specified creepage distances, and secure conductor clamping. This unit covers terminals, the critical tE time for motors, cable gland selection, and inspection requirements.
Learning Objectives
Explain how Ex e prevents ignition and why sparking components are not permitted inside Ex e enclosures
Define creepage distance, clearance distance, and Comparative Tracking Index (CTI)
Explain tE time and state why the overload relay setting is a safety-critical function
State the cable gland accessories required for threaded and unthreaded entries in metallic and plastic enclosures
Identify inspection faults specific to Ex e equipment including terminal overloading and damaged IP seals
4.2 Protection Concept — Ex e
Increased safety prevents ignition by eliminating sources of ignition through quality of construction rather than by containing or excluding flammable gas. The letter "e" derives from the German Erhöhte Sicherheit (increased security), reflecting the concept's German origins as an alternative to flameproof.
IEC 60079-7 Definition
A type of protection applied to electrical apparatus in which additional measures are taken to give increased security against the possibility of excessive temperatures and of the occurrence of arcs and sparks in normal service or under specified fault conditions.
The critical distinction from Ex d: increased safety enclosures are NOT designed to contain an internal explosion. They do not have flamepaths. Safety depends on preventing arcs, sparks, and excessive temperatures from occurring in the first place. This is achieved through: mechanically strong impact-resistant enclosures; minimum IP54 ingress protection; certified de-rated terminals with positive locking devices; specified creepage and clearance distances; and controlled thermal performance.
Equipment Protection Level: Gb. ATEX Category 2 and 3. Zone 1 and Zone 2. Certified for all Group II gas subdivisions IIA, IIB, IIC. Ambient: -20°C to +40°C unless otherwise marked. Typical applications: junction boxes, lighting fittings, induction motors.
4.5 Increased Safety Terminals
Terminals inside Ex e enclosures must be component-certified. They are manufactured from high-quality materials including Melamine, Polyamide, and ceramic, all with high Comparative Tracking Index (CTI) values indicating resistance to surface tracking. They incorporate positive locking devices to prevent conductors from loosening due to vibration.
Parameter
Definition
Significance
Clearance distance
Shortest distance through air between two conductors
Flash-over path — must be maintained at minimum specified value
Creepage distance
Shortest distance between conductors along insulator surface
Tracking path — contamination can bridge this distance
CTI
Resistance of material to surface tracking under drip electrolyte test
Higher CTI = better resistance to tracking under contamination
Terminal De-rating
Ex e terminals are de-rated to approximately 50% of standard industrial current ratings to limit internal temperature rise. This is a fundamental requirement — using terminals at standard industrial ratings in an Ex e enclosure constitutes an unauthorised modification.
Terminal Type
Conductor Size
Ex e Max Current (A)
Standard Industrial Max (A)
SAK 2.5
2.5mm²
15
27
SAK 4
4mm²
21
36
SAK 6
6mm²
26
47
SAK 10
10mm²
37
65
SAK 16
16mm²
47
87
SAK 35
35mm²
75
145
Terminal Population Limits
The number of terminals of a given size that may be installed in a specific enclosure is limited by the enclosure certification — to control the total temperature rise within the certified thermal limits. The manufacturer's data provides the permitted type, size, current rating, and maximum quantity of terminals for each certified enclosure size.
⚠ Terminal Overloading
Installing more conductors than certified, using larger cross-sections, or using piggyback connectors to squeeze extra circuits into a terminal block all: reduce creepage distances below certified values; increase temperature rise above tested levels. Category A deficiency. The enclosure must be replaced with one correctly rated for the actual circuit count.
4.8 Increased Safety Ex e Motors
Ex e motors are similar in appearance to standard induction motors. The key safety difference is the requirement for the overload relay to trip within the tE time under locked-rotor conditions.
tE Time
The time (in seconds) taken for the motor windings to reach the maximum permissible temperature (determined by T-class) from their maximum normal operating temperature, when carrying the locked-rotor starting current IA at maximum ambient temperature. The thermal overload relay must trip within this time when the motor stalls.
The tE time and the starting current ratio IA/IN (ratio of starting current to full-load current) are both marked on the motor nameplate. These are used to set the overload relay and to verify its operation during commissioning.
⚠ Overload Relay — Safety-Critical Setting
The overload relay must be set and verified to trip within tE at the motor stall current. This is a mandatory Detailed inspection item at commissioning. If the relay is set too slowly (e.g. 25 seconds when tE is 12 seconds), the motor windings will reach the T-class limiting temperature under locked-rotor conditions — the motor's surface temperature could then exceed the marked T-class, creating an ignition source in the hazardous area.
4.6–4.7 Cable Gland Selection for Ex e
Ex e enclosures do not have a flamepath. The cable gland is needed only to: maintain enclosure IP rating; provide mechanical cable support; and provide armour earth continuity path. A barrier gland is not required — any certified Ex e gland or dual-certified Ex d/Ex e gland is acceptable.
#
Enclosure Type and Entry
Required Accessories
1
Metal enclosure, threaded entry ≥6mm wall thickness
Gland only (thread provides adequate IP seal)
2
Metal enclosure, threaded entry <6mm wall
Gland + IP sealing washer (to maintain IP54+)
3
Metal enclosure, clearance hole (unthreaded), no removable gland plate
Gland + IP washer on outside + serrated washer + locknut inside
4
Metal enclosure, clearance hole, with removable gland plate
Gland + earth tag + IP washer on outside + serrated washer + locknut inside
5
Plastic (non-conductive) enclosure, clearance hole, no internal continuity plate
Gland + earth tag + IP washer on outside + locknut inside
Unused cable entries in Ex e enclosures may be closed using certified Ex e blanking plugs or certified stopping plugs that maintain the IP rating of the enclosure.
4.9 Inspection of Ex e Equipment
Inspection Item
Deficiency if Wrong
Grade
All cover bolts fitted and tight
Missing bolt — IP integrity compromised — Category A
Visual
Unused entries sealed with certified Ex e blanking plugs
Unsealed entry — IP compromised — Category A
Visual
IP seal (gasket) undamaged and correctly seated
Cracked or missing gasket — Category A (IP lost, creepage reduced)
Close
Cable gland accessories correctly installed for entry type
Missing IP washer on clearance hole entry — Category A
Close
Conductors secure in terminals — no more than 1mm exposed between insulation and terminal
Loose conductor — Category A (arcing risk)
Close/Detailed
One conductor per terminal side (unless certification permits more)
Double-terminated terminal — Category A
Detailed
Terminal population within certified limits
Overloaded — Category A
Detailed
Overload relay setting verified against tE time
Relay too slow — Category A (potential surface overtemperature)
Detailed
T-class correct for area gas
Incorrect T-class — Category X
Visual
Unit 4 Knowledge Check — 10 Questions
CompEx-style questions covering the full unit content.
Q1Unit {num}
A conductor is found with 3mm of bare copper exposed between the cable core insulation and the terminal in an Ex e junction box. What is the deficiency?
No more than 1mm of bare conductor should be exposed between the cable core insulation and the metal of the terminal. Excessive bare conductor creates a risk of arcing between adjacent terminals and reduces creepage distances. This is a Category A deficiency.Ref: IEC 60079-7 — Terminal Connection Requirements
Q2Unit {num}
An Ex e motor nameplate shows tE = 12 seconds, IA/IN = 5.5. The motor starter thermal relay is set to trip at 18 seconds. Is this correct?
The thermal relay must trip within tE = 12 seconds under locked-rotor conditions. A relay set to 18 seconds will allow the windings to heat beyond the T-class limiting temperature. This is a Category A deficiency — the relay must be correctly set and the correct setting must be verified during Detailed inspection at commissioning.Ref: IEC 60079-7 — tE Time Compliance
Q3Unit {num}
Can a switch be installed directly inside an Ex e junction box?
Ex e prevents ignition by ensuring no arcing or sparking occurs inside the enclosure. A switch by definition produces arcs when it opens and closes a circuit under load. Installing a switch directly inside an Ex e enclosure defeats the protection concept. Switches must either be Ex d protected (with their own flamepath enclosure) or use another suitable protection method.Ref: IEC 60079-7 — Protection Principle
Q4Unit {num}
What is the minimum ingress protection rating required for an Ex e enclosure?
The minimum ingress protection for Ex e enclosures is IP54. Ex n (Type N) motor enclosures may use IP44 where only insulated parts are enclosed. IP20 is the minimum for some IS apparatus enclosures (associated apparatus in safe areas). Ex e requires IP54 as a minimum.Ref: IEC 60079-7 — IP Rating Requirements
Q5Unit {num}
A plastic (non-conductive material) Ex e enclosure has clearance-hole cable entries and no internal earth continuity plate. Which cable gland accessories are required?
Plastic enclosures are non-conductive. The cable armour earth cannot flow through the plastic body to the earth bar — an earth tag (banjo) must be fitted to provide the armour earth path directly. No serrated washer is needed because there is no conductive face to maintain continuity through. IP washer maintains IP at the clearance-hole interface. Locknut secures the assembly.Ref: IEC 60079-7 / IEC 60079-14 — Non-Conductive Enclosures
Q6Unit {num}
What IEC 60079 standard governs the construction of Ex e equipment?
IEC 60079-7 (BS EN 60079-7) is the construction standard for increased safety Ex e equipment. IEC 60079-0 covers general requirements applicable to all Ex equipment. IEC 60079-1 is the Ex d flameproof standard. IEC 60079-14 is the code of practice for electrical installations.Ref: IEC 60079-7 — Construction Standard
Q7Unit {num}
After 2007, what type of cable glands are required for Ex e enclosures?
After 2007, IEC 60079-0 requires that only certified cable glands are used with Increased Safety enclosures. This requirement also applies to Ex d motors with Ex e terminal box assemblies. Prior to 2007, uncertified glands were permissible for Ex e if they met a 7J impact test and maintained IP — this is no longer acceptable under current standards.Ref: IEC 60079-0 / IEC 60079-7 (post-2007)
Q8Unit {num}
A conductor from one cable gland is routed across the junction box and loomed together with conductors from a different cable gland. What deficiency does this create?
The cores from different cable glands must not be combined in a single loom inside an Ex e enclosure. Different glands may carry circuits of different voltage levels — looming them together can reduce effective clearance distances between circuits and increase fault risk. This is a Category A deficiency.Ref: IEC 60079-7 / IEC 60079-17 — Inspection of Ex e
Q9Unit {num}
During a Close inspection, the IP gasket in an Ex e enclosure cover is found to be cracked. What category and required action?
A cracked IP gasket is a Category A deficiency. It reduces the ingress protection of the enclosure, allowing moisture and contamination to enter — which reduces creepage distances inside the enclosure and risks tracking. The gasket must be replaced with the manufacturer-approved type before the enclosure is returned to service.Ref: IEC 60079-17 — Inspection of Ex e
Q10Unit {num}
Partitions are found missing from either side of link connections in an Ex e terminal box. What concern does this raise?
Partitions on either side of links or jumper connections in Ex e terminal blocks maintain the certified creepage distances between circuits. Without partitions, adjacent circuits can fall below the required creepage separation — reducing insulation integrity under contamination conditions. Missing partitions are a Category A deficiency.Ref: IEC 60079-7 / IEC 60079-17