For most three-phase 230/400V installations, a Type 2 SPD with Uc 275V AC wired in 3+1 mode covers standard distribution-board protection, with conductor ≥6mm² Cu, dedicated 32–63A Type B/C MCB, and total lead length L1+L2+L3 ≤0.5m [S2][S1].
The selection logic is set by four IEC 61643-11 parameters, not by load current: Uc (maximum continuous operating voltage), In (nominal discharge current, 8/20µs), Imax (maximum discharge current, 8/20µs), and Up (voltage protection level). Earthing system type decides pole count and protection mode; installation position decides Type 1, Type 2, or combined Type 1+2 [S2].
Type 1, Type 2, and Type 1+2: Test Waveform and Position
IEC 61643-11 classifies SPDs by the test waveform they must survive, which is the only reliable way to match device to position [S2]. A Type 1 SPD is rated to the 10/350µs Iimp waveform and is installed at the main panel or service entrance when an external lightning protection system (LPS) is present or the building is directly exposed to lightning. A Type 2 SPD is rated to the 8/20µs In/Imax waveform and is the standard device for distribution boards and sub-panels in industrial and commercial sites. A Type 1+2 device carries both ratings and is used at the main panel where space is limited and combined protection is needed in one module [S2].
Type 3 devices sit downstream as fine protection close to sensitive equipment, with lower let-through but no standalone surge-handling capability. The 2026 NF C 15-100 framework (effective from September 2025) makes main surge arresters mandatory across 7 categories of buildings, up from 4 previously, which is the main regulatory driver behind the wider Type 1 and Type 2 specification seen in current French installations [S3].
The Four Sizing Parameters and Their Real Values
Uc must equal or exceed the system's maximum continuous operating voltage, and 275V AC is the standard selection for 230/400V TN-S/TT systems [S2]. In for Type 2 is typically 5–20kA (8/20µs), while Imax sits in the 5–40kA band depending on exposure [S2][S3]. Type 1 Iimp values are commonly rated at 25kA (10/350µs) at the service entrance [S3]. Up, the voltage protection level, must be lower than the impulse withstand of the equipment being protected, and the installed Up is set by the lead length, not the device label.
For DC photovoltaic strings, only an IEC 61643-31 certified DC SPD may be used; an AC SPD on a PV string is a misapplication [S1]. DC lead length is held to ≤0.5m and a DC-rated gPV fuse is required in series. Conductor cross-section for the DC string is ≥4mm² Cu, half the AC Type 2 requirement, because PV surge currents are lower but the DC arc does not self-extinguish [S1].
50cm Lead Rule and the Installed Up Penalty
The 50cm rule (IEC 60364-5-53) is the most violated rule in field installations, and the one that decides whether the SPD actually does its job [S1]. Every additional 10cm of lead length adds approximately 1kV of residual surge voltage above the device's rated Up at the equipment terminals. A Type 2 SPD with a 2.5kV Up label can deliver 3.5kV installed Up at 1m of lead, exceeding the impulse withstand of most distribution equipment and partially defeating the protection [S1].
Practical enforcement: mount the SPD on the DIN rail slot closest to the busbar entry, measure the lead path before drilling, and if total L1+L2+L3 exceeds 0.5m, choose a closer mounting point or upsize to a Type 1+2 device with lower Up. For background on how a surge protector fits inside a coordinated protection chain, the linked reference lays out the device classes and the upstream/downstream split.
MCB Coordination and Conductor Sizing by Type
Never connect an SPD directly to the busbar; a dedicated overcurrent device is mandatory, sized to the SPD type and the conductor cross-section [S1]. Type 2 AC SPD: ≥6mm² Cu conductor, 32–63A Type B or C MCB, 1-pole for single-phase, 3-pole for three-phase. Type 1 AC SPD: ≥16mm² Cu conductor, 100–125A MCB. DC PV SPD: ≥4mm² Cu, DC-rated gPV fuse, never an AC MCB. The MCB is for the SPD branch only and must not be shared with other loads [S1].
Conductor sizing scales with surge current handling: Type 1 must dissipate partial lightning current (10/350µs) and needs the larger 16mm² Cu to limit temperature rise during the event. Type 2 only sees 8/20µs waves with lower charge, so 6mm² Cu is adequate when paired with the thermal disconnector inside the SPD. The N conductor on AC SPDs is wired direct to the neutral busbar (no MCB), and the PE conductor is wired direct to the earth busbar with a straight, loop-free run [S1][S2].
Earthing System and Wiring Mode (1+0, 1+1, 3+0, 3+1)
Mode is set by the earthing system, not by panel size or load current [S2]. TN-S/TT systems use 1+1 mode for single-phase (L via MCB, N direct, PE direct) and 3+1 mode for three-phase (L1/L2/L3 via 3-pole MCB, N direct, PE direct). TN-C systems (PEN conductor) use 1+0 mode for single-phase and 3+0 mode for three-phase; adding N–PE protection on TN-C creates a fault path because N and PE are the same conductor [S1].
For three-phase 230/400V industrial panels, 3+1 mode is the default because most factory loads are connected L-N (230V) and a single L-PE-only device leaves the L-N insulation stressed. The four live conductors (L1, L2, L3, N) all need clamping paths to PE; missing the N–PE path is the most common reason a 3-phase SPD fails an installation audit [S2].
Comparison: Type 1 vs Type 2 vs Type 1+2 vs Type 3
Across the four IEC 61643-11 device classes, the decision criteria are waveform survival, install position, conductor size, and MCB rating [S2][S1]. Type 1: 10/350µs waveform, service entrance only when LPS present, ≥16mm² Cu, 100–125A MCB. Type 2: 8/20µs waveform, distribution board, ≥6mm² Cu, 32–63A MCB. Type 1+2: both waveforms in one module, main panel where space is tight, conductor and MCB per the higher of the two ratings. Type 3: 8/20µs with low Up, mounted within a few metres of the equipment, no MCB of its own but a Type 2 upstream is mandatory [S2][S3].
Who should NOT pick the mainstream Type 2 as the only device: any site with an external LPS, any rooftop PV inverter, any building with a long service entrance cable run, and any EV charging hub where a surge event can run into €35,000 of damage to the charging infrastructure [S3]. These sites need Type 1 at the service entrance plus Type 2 at the sub-panel plus Type 3 at the load. For chemical and process plants, the linked Best SPD for Chemical Processing: Spec Map and Selection Criteria deep-dives the Ex-area and corrosive-atmosphere choices.
Limitations, Failure Modes, and Standards Discipline
Failure modes in field installations cluster around four issues: lead length over 0.5m, shared MCB with other loads, wrong mode for the earthing system, and AC SPDs on DC PV strings [S1][S2]. Capacitor-bank switching alone generates 2–3× nominal line-voltage transients with sub-1µs rise times daily, and these events degrade unprotected electronics gradually rather than blowing them up, so the root cause is often missed in post-failure reviews [S2].
Standards to anchor the specification: IEC 61643-11 for low-voltage AC SPDs, IEC 61643-31 for DC PV SPDs, and IEC 60364-5-53 for the 50cm lead rule and installation practice [S1][S2]. For 2026 French installations, NF C 15-100 sets the building categories that trigger mandatory main surge arrester specification [S3]. Sourcing side: when consolidating a bill of materials, a structured Terminal Block Suppliers and Manufacturers: 2026 Supply Map helps coordinate the SPD, MCB, and DIN-rail layout for the panel build.
Selection shortlist in order: confirm earthing system (TN-S/TT/TN-C/IT) and pick mode; confirm LPS presence to decide Type 1 vs Type 2 at the main panel; size Uc ≥ system max continuous voltage (275V AC standard for 230/400V); pick In/Imax from exposure class (20–40kA Imax for exposed sites, 5–20kA for clean indoor); enforce ≤0.5m lead and dedicated MCB; for PV strings, swap to an IEC 61643-31 DC device with a gPV fuse; add Type 3 within 5m of any sensitive load (PLCs, VFDs, EV chargers). Verify green status indicator at commissioning, log the installed Up at the terminals, and re-test after any panel modification.
Spec-level background on the components involved: protective clothing, and linear guide.