Direct and Induced Lightning in Three-Phase LV Distribution
Market Background
Low-voltage distribution systems in industrial and commercial facilities face two different surge events: direct lightning current entering through external conductors, and induced surges coupled onto cabling by nearby strikes. A surge protection device rated for only one of these events leaves a gap. For this reason, specification documents increasingly call for a combined T1+T2 device at the main distribution level, where both energy levels must be handled by one coordinated component.
Customer & Application Scenario
A mid-sized manufacturing plant operates a three-phase 220 Vac distribution system feeding motor control centers, lighting panels, and workshop sub-boards. The main incoming panel had no surge protection at all, and the site had experienced repeated damage to variable-frequency drives and control relays after storm seasons. The maintenance team wanted a single device installed at the main panel rather than a cascade of separate units.
Our Solution
The facility installed the LPM H12.5-280/3+NPE, a combined T1+T2 surge protection device built on a MOV + GDT hybrid circuit. The unit is wired in a 3+NPE (3+1) configuration and protects the L-N paths and the N-E path with dedicated components.
Key design points relevant to a main-panel installation:
- Lightning current capability: Iimp 12.5 kA (10/350 µs) on L-N, and 20 kA (10/350 µs) on N-E — covering the direct-strike portion of the event.
- Nominal discharge current: In 30 kA (8/20 µs) on L-N, 50 kA (8/20 µs) on N-E — covering the induced portion.
- Voltage protection level: Up ≤1.5 kV across all protected paths.
- Response time: tA ≤25 ns on the MOV path, ≤100 ns on the GDT path.
- Installation: DIN 35 mm rail, 90 × 72 × 80 mm housing, wiring cross-section 2.5–32 mm², terminal torque 5 N·m, strip length 12 mm.
- Lightning protection zone: suitable for installation at LPZ 0A-B and subsequent zones.
The enclosure uses mineral nylon PA6 with a V0 flame-retardant rating, and the operating range covers −40 °C to +80 °C indoors at IP20.
Customer Feedback
"We fitted one module at the main panel instead of building a multi-stage arrangement. Commissioning was straightforward on the existing 35 mm rail, and the wider terminal range accepted the existing feeder conductors without re-terminating the busbar." — replace with verified customer statement
Summary: Key Technical Parameters
|
Parameter |
Value |
|
Standard / Type |
GB/T 18802.11-2020; SPD type T1, T2 |
|
Protection components |
L-N: MOV; N-E: GDT |
|
Un |
220 Vac (50 Hz) |
|
Uc |
280 Vac (L-N) / 255 Vac (N-E) |
|
In (8/20 µs) |
30 kA (L-N) / 50 kA (N-E) |
|
Iimp (10/350 µs) |
12.5 kA (L-N) / 20 kA (N-E) |
|
Up |
≤1.5 kV |
|
Response time tA |
≤25 ns (L-N) / ≤100 ns (N-E) |
|
Protected modes |
L1, L2, L3-N, N-E |
Conclusion
For three-phase low-voltage main panels exposed to both direct and induced surges, a combined T1+T2 device removes the coordination problem of a staged design. The LPM H12.5-280/3+NPE provides documented Iimp and In ratings on both the L-N and N-E paths, a defined Up value, and a DIN-rail footprint that fits standard switchgear assemblies.
