UL248-13 is the official standard for semiconductor fuses (aR and gR categories) used in inverters, solar PV, servo drives, and IGBT protection systems.
Most fuse manufacturers and engineers are confused about how many samples are required for UL248-13 certification for the full range from 50A to 400A.
This article explains the official UL family test policy, exact sample breakdown, destructive test rules, and forbidden operations during UL witness testing.
1. What Is UL248-13 Family Test Rule?
UL248-13 allows family certification for multi-current range fuses if the products share identical core structures.
A full 50A–400A series can be covered under one UL file if all below conditions are identical:
- Ceramic housing dimension and material
- Terminal structure, size, and material
- Quartz sand filling density and formula
- Sealing glue and end cap structure
- Internal assembly process
Only the fuse element thickness or width can be changed to adjust different current ratings.
Under family test policy:
- Maximum current model (400A) = master test unit (full destructive tests)
- All smaller current models (50A–315A) = covered by structural equivalence (no full breaking tests)
This rule saves massive certification cost and test time.
2. Master Model: 400A Full Test Sample Quantity
The 400A aR fuse is the main tested model for the entire 50–400A series. It needs to complete all UL248-13 witness tests.
Total required samples for 400A: 20 PCS
These samples are allocated for all core certification items:
- Temperature rise test
- Time-current characteristic (TCC) curve testing
- Low breaking capacity test
- Maximum I²t energy test
- Rated short-circuit breaking capacity test
- Withstand voltage and insulation test
- Thermal shock and mechanical endurance inspection
All high-risk and high-cost destructive tests are completed on the 400A master model only.
3. Covered Models: 50A–315A Sample Quantity
All smaller current specifications do not need short-circuit breaking tests.
They only require structural verification, resistance testing, and appearance consistency inspection.
Each specification requires 4 PCS:
- 50A: 4 PCS
- 80A: 4 PCS
- 100A: 4 PCS
- 160A: 4 PCS
- 200A: 4 PCS
- 250A: 4 PCS
- 315A: 4 PCS
Total covered samples: 28 PCS
These samples prove structural consistency with the 400A master model to comply with UL family test auditing rules.
4. Full Series Total Sample Summary
| Model Type | Current Range | Quantity | Test Type |
|---|---|---|---|
| Master Model | 400A | 20 PCS | Full UL248-13 destructive witness tests |
| Covered Models | 50A–315A | 28 PCS | Structure check, resistance verification, appearance audit |
| Total | 50A–400A | 48 PCS | Complete series certification |
For factory safety stock and possible laboratory retest demands, the recommended preparation quantity is 50 PCS total.
5. Strict UL Rule: No Sample Reuse
UL248-13 has a strict non-negotiable rule:
Temperature rise test samples CANNOT be used for breaking tests
After long-duration full-load current heating:
- The fuse element produces thermal fatigue
- Internal material stress changes
- Quartz sand thermal stability declines
Reusing warmed samples for short-circuit tests will cause breaking failure and direct certification rejection during UL witness tests.
All breaking capacity tests must use brand-new, unused samples.
6. Other Forbidden Certification Mistakes
- Different sealing glue or sand density for different currents Will break family equivalence and force separate full tests for each rating.
- Different terminal or ceramic size between small and large currents UL will split your series into multiple independent test families.
- Inconsistent printing or marking standards Causes labeling audit failure.
7. Why Family Test Is the Best Solution
For 50A–400A aR fuse series:
- Single master model test reduces 70%+ certification cost
- Shortens test cycle significantly
- Maintains unified production process and structural consistency
- Fully compliant with UL248-13 official policy
FAQ
1: Do I need to test breaking capacity for 50A, 100A, 200A models?
No. Under UL248-13 family rules, only the maximum 400A model needs short-circuit breaking tests.
2: Can temperature rise samples be reused?
No. Heated samples are thermally fatigued and are prohibited for destructive breaking tests.
3: How many samples are needed for full 50–400A UL248-13 certification?
Standard official quantity is 48 PCS; factory recommended stock is 50 PCS.
4: What conditions are required for UL family test approval?
All housing, terminal, filling sand, sealing structure, and assembly processes must be identical across the entire current range.
Q5: Will different fuse element size affect family test approval?
No. Adjusting fuse element thickness for different current ratings is explicitly allowed in UL248-13 family policies.
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