The shift from Type Tested Assemblies (TTA) and Partially Type Tested Assemblies (PTTA) to Verified Assemblies under IEC 61439 marks a significant evolution in low-voltage switchgear and controlgear standards. For enclosure manufacturers, panel builders, and electrical engineers, understanding this transition is crucial for compliance, safety, and performance optimization.
At EnclosureExpert.com, we specialize in helping professionals navigate these changes. In this article, we’ll explore:
- Why IEC 61439 replaced TTA/PTTA
- Key differences between old and new verification methods
- How Verified Assemblies improve safety and reliability
- Best practices for compliance
Why Did IEC 61439 Replace TTA/PTTA?
The IEC 60439 standard (predecessor to IEC 61439) had several shortcomings:
- Ambiguity in Responsibility – The roles of Original Manufacturers (OEMs) and Assembly Manufacturers (panel builders) were unclear, leading to compliance gaps 4.
- Limited Scope – TTA/PTTA classifications didn’t cover all assembly variations, leaving some untested 2.
- Inconsistent Testing – Many assemblies worldwide (up to 80%) were non-compliant due to vague requirements 4.
IEC 61439 addressed these issues by introducing Verified Assemblies, ensuring:
✔ Clearer accountability (who tests what)
✔ More rigorous verification methods (testing, calculation, design rules)
✔ Better traceability (documentation requirements)
Key Differences: TTA/PTTA vs. Verified Assemblies
| Aspect | TTA/PTTA (IEC 60439) | Verified Assemblies (IEC 61439) |
|---|---|---|
| Terminology | Type Tested / Partially Tested | Verified (design & routine tests) |
| Responsibility | Unclear roles | OEM (design verification) + Panel Builder (routine verification) 4 |
| Testing Methods | Limited type-testing | 3 Verification Methods: Testing, Calculation, Design Rules 14 |
| Documentation | Minimal requirements | Strict records for traceability & compliance 1 |
| Flexibility | Rigid categories | Adaptable to custom assemblies |
How Verified Assemblies Under IEC 61439 is Improve Safety & Reliability
1. Enhanced Verification Processes
Under IEC 61439, assemblies must pass 12 key tests, including:
- Temperature rise (critical for heat dissipation) 14
- Short-circuit withstand (prevents fire hazards) 1
- Dielectric strength (ensures insulation integrity) 14
- Mechanical impact (IK rating) (durability of enclosures) 14
2. Clearer Roles & Accountability
- Original Manufacturer → Validates design via testing/calculations.
- Assembly Manufacturer → Conducts routine verifications (e.g., torque checks, IP ratings) 4.
3. Future-Proofing for New Technologies
- Supports photovoltaic (PV) systems and EV charging stations, requiring RDF (Rated Diversity Factor) = 1 for continuous loads 8.
Best Practices for Compliance with Verified Assemblies
- Use Pre-Verified Components
- Leverage OEM-tested busbars, enclosures, and switchgear (e.g., Wöhner’s pre-calculated short-circuit ratings) 1.
- Maintain Detailed Documentation
- Keep records of design verifications, test reports, and conformity declarations 4.
- Follow Routine Verification Checklists
- Ensure IP ratings, torque settings, and grounding meet standards 10.
- Utilize Digital Tools
- Software like Wöhner’s configurator helps verify current-carrying capacity and short-circuit ratings 1.
Conclusion: Why This Matters for Enclosure Experts
The shift from TTA/PTTA to Verified Assemblies under IEC 61439 ensures:
✅ Higher safety standards (reducing fire/electrical risks)
✅ Better-defined responsibilities (avoiding compliance gaps)
✅ More adaptable testing (supporting custom designs)
For enclosure manufacturers and panel builders, adopting these changes means fewer failures, longer product lifespans, and compliance with global standards.
Need expert guidance on IEC 61439 compliance?
📩 Contact EnclosureExpert.com for tailored solutions!