In the world of hazardous areas—where gas, vapors, and dust create explosive atmospheres—the default mindset is often “containment.” Engineers frequently rely on heavy, expensive Flameproof (Ex d) enclosures designed to withstand an internal explosion.
However, there is a smarter, lighter, and often more cost-effective approach that focuses on prevention rather than containment. This is Protection Technique “e”, commonly known as Increased Safety.
If you are an electrical engineer, procurement specialist, or maintenance manager dealing with IEC 60079-7 standards, this guide explores how “Ex e” applies specifically to electric motors and electrical panels, covering details often missed in standard manuals.
What is Protection Type “e” (Increased Safety)?
Unlike Flameproof (Ex d) equipment, which assumes an explosion will happen inside and tries to stop it from escaping, Increased Safety (Ex e) operates on a different philosophy: Ensure that arcs, sparks, or excessive temperatures never occur in the first place.
This protection method is applied to electrical equipment that, during normal operation, does not produce arcs or sparks. The “Increased Safety” standard imposes additional measures to provide a higher degree of safety.
The Core Principles of Ex e:
- High-Quality Insulation: Prevents breakdown and short circuits.
- Enhanced Creepage and Clearance: Wider distances between conductive parts to prevent tracking.
- Secure Connections: Terminals designed to never loosen under vibration (anti-self-loosening).
- Minimum IP Rating: Usually IP54 or IP65 to keep dust and water out, protecting the internal components from degradation.
The Ex e Motor: A Masterclass in Efficiency
Using an Ex e motor is a game-changer compared to the bulky cast-iron Ex d motors. However, not every motor can be Ex e certified. It is typically limited to squirrel cage induction motors because they do not use brushes (which spark).
Here is the technical breakdown of how an Ex e motor differs from a standard industrial motor:
1. The Critical Concept of “tE Time”
This is the most unique aspect of Ex e motors and is rarely explained clearly.
If an Ex e motor stalls (locked rotor), it heats up rapidly. The tE time is the time it takes for the motor windings to heat up from their operating temperature to the maximum safe temperature limit (T-Class) under a locked rotor condition.
- Why it matters: Your overload protection device (thermal relay or breaker) must trip before the tE time is reached.
- The Rule: If the tE time is 10 seconds, your protection device must cut power in less than 10 seconds during a stall.
2. Rotor and Stator Construction
To keep temperatures low, Ex e motors use higher quality magnetic steel and slightly larger air gaps to reduce stray load losses. This often makes Ex e motors run cooler and more efficiently than their standard counterparts.
3. The “Non-Sparking” Fan
The external cooling fan on an Ex e motor must be made of non-static material (often conductive plastic or non-ferrous metal) and positioned so that even if the cowl is dented, the fan will not rub against it and create friction sparks.
Ex e in Electrical Panels and Junction Boxes
While you cannot put sparking components (like standard contactors or circuit breakers) inside a standard Ex e enclosure, “Increased Safety” is the industry standard for terminal boxes and control stations.
Why Choose Ex e Panels over Ex d?
- Weight: Ex e enclosures can be made of GRP (Glass Reinforced Polyester), plastic, or thin stainless steel. They are significantly lighter than Ex d cast metal boxes.
- Accessibility: Ex e boxes usually feature hinged doors. Ex d boxes often require removing dozens of bolts to access the internals.
- Corrosion Resistance: GRP and Stainless Steel offer superior resistance in offshore or chemical plant environments compared to painted cast iron.
The “Modular” Approach
Modern hazardous area design often uses a hybrid approach. Engineers will place sparking components (switches/breakers) inside small, specialized Ex d components, and then house those components inside a larger Ex e enclosure. This creates a panel that is easy to wire (Ex e terminals) but safely controls power.
Comparison: Ex e vs. Ex d
To help you decide which is right for your facility, here is a quick comparison:
| Feature | Protection “e” (Increased Safety) | Protection “d” (Flameproof) |
|---|---|---|
| Philosophy | Prevent ignition source creation. | Contain the explosion internally. |
| Enclosure Material | Plastic, GRP, Stainless Steel (Thin). | Cast Iron, Cast Aluminum, Heavy Steel. |
| Weight | Light. | Very Heavy. |
| Cabling | Standard glands (usually). | Barrier glands (often required). |
| Maintenance | Easy access for inspection. | Difficult (machined flame paths must be protected). |
| Cost | Generally lower installation cost. | Higher hardware and installation cost. |
Maintenance and Inspection of Ex e Equipment
For maintenance teams, the “Increased Safety” designation requires specific checks during routine inspections (IEC 60079-17):
- Terminal Tightness: Check for loose connections. Heat caused by loose resistance is the #1 enemy of Ex e.
- Gasket Integrity: Since Ex e relies on keeping the environment out (IP rating), the rubber seals on junction boxes and motor terminal covers must be pristine. Cracks compromise the safety rating.
- No Modifications: You cannot drill extra holes in an Ex e enclosure without voiding the certification, as this alters the IP rating and physical strength.
Conclusion
Protection Technique “e” represents a shift from brute force to precision engineering. By utilizing Increased Safety motors and panels, facilities can reduce weight, lower maintenance costs, and improve corrosion resistance without sacrificing safety.
However, success with Ex e requires knowledge. It requires correctly setting the overload protection based on tE time and ensuring that terminal connections remain tight. When implemented correctly, Ex e is the modern standard for safety in Zone 1 and Zone 2 environments.
