50W = V‑0/V‑1/V‑2 (20 mm flame, IEC 60695‑11‑10)
500W = 5VA /5VB (125 mm flame, IEC 60695‑11‑20)
1. Core rule
Follow the requirement of end-product safety standard / customer specification. This is the #1 rule. If your product standard or drawing specifies 5VA/5VB → choose 500W flame. If it only requires V‑0/V‑1/V‑2 → choose 50W flame.
2. Difference of test objects & risk scenario
✅ Choose 50W flame (V0/V1/V2)
2.1 Purpose: Evaluate reaction to small low-energy ignition source (minor electrical fault, small hot spot)
2.2 Specimen: only bar specimens (125 ×13 mm), vertical mounting
2.3 Flame: 20 mm blue flame, apply twice, 10 s each time
2.4 Typical applications:
2.4.1 Common consumer electronics housing, adapter, PCB support, small internal insulation
2.4.2 Low/medium power electrical parts with low risk of sustained strong flame attack
2.4.3 Most IEC 62368-1 general plastic components
✅ Choose 500W flame (5VA /5VB)
2.5 Purpose: Evaluate resistance to strong repeated flame attack + burn-through risk
2.6 Specimen: bar specimens + plaque plate (150×150 mm)
2.7 Flame: 125 mm flame, apply 5 times ×5 s, interval 5 s, burner tilted 20°
2.8 Typical applications (high fire risk enclosure):
2.8.1 High-voltage cabinet, energy storage / battery enclosure, large power supply housing
2.8.2 Parts where enclosure integrity must survive severe local flame exposure
2.8.4 Customer or product standard explicitly calling for 5VA or 5VB
Precondition: Material must first pass V‑0 or V‑1 before 5V classification can be granted.
5VA: No burn-through hole on plaque, no flaming drips igniting cotton\
5VB: Burn-through hole allowed, no flaming drips igniting cotton
3. Quick selection checklist
| Item |
50W (V grade) |
500W (5V grade) |
| Flame power |
50 W, 20 mm |
500 W,125 mm |
| Specimen |
Bar only |
Bar + plaque plate |
| Main evaluation |
After-flame, afterglow, dripping |
After-flame, afterglow, dripping + burn-through |
| Fire hazard |
Small ignition source |
Intense, repeated flame attack |
| Common requirement |
General electronics plastic parts |
High-risk power / battery enclosure |
4. Important notes
4.1.500W test is more expensive and stricter; material cost will also rise for 5VA/5VB grade. Do not select 500W unless required.
4.2.Rating is thickness dependent. V0 @1.6 mm does not equal V0 @0.8 mm; same for 5VA/5VB.
4.3.UL94 only gives small-scale lab classification. It cannot fully represent real fire performance of finished product.
5. Simple decision sentence
Use 50W flame for normal plastic components requiring V0/V1/V2.
Use 500W flame when the enclosure needs to resist strong flame penetration and specification requires 5VA or 5VB.
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