A Type 1 surge protector, or parafoudre type 1, is the device rated to conduct a direct lightning current strike (10/350 µs waveform) safely to ground at the point where power enters a building. You need one when the building carries a lightning rod (paratonnerre), when the SPD sits at the origin of the installation (TGBT), or when the low-voltage supply is aerial in a zone with a lightning density (Nk) above 25. The number to check first is minimum discharge current, or Iimp.

  • Building fitted with a paratonnerre → Type 1 is mandatory at the origin of the installation
  • Aerial LV supply in a zone with Nk>25 → Type 1 applies per NF C 15-100
  • ERP, ICPE, or IGH classification → often triggers stricter obligations regardless of supply type

Iimp minimum: Most specifications start at 12.5 kA per pole (10/350 µs), with higher values required as lightning protection level rises, per EN 62305-2 guidance.

Key Takeaways

A compliant Type 1 installation depends equally on correct Iimp/Up/Ifi sizing and on wiring discipline, especially the 50 cm loop rule, at the point of installation.

PointDetails
Confirm the triggerParatonnerre, aerial supply in Nk>25 zones, or ERP/ICPE/IGH status all mandate Type 1 review.
Size to protection levelMatch Iimp (12.5 to 35 kA) to the site’s LPL under EN 62305-2, with margin for critical loads.
Check Ifi against IccAuto-extinction current must exceed available short-circuit current or the device won’t reset.
Enforce the 50 cm ruleLong conductor loops add impedance that undermines even a correctly rated device.
Work with a full-cycle providerIndelec pairs risk assessment, device selection, installation, and certification under one engagement.

Table of Contents

What Makes a Type 1 Surge Protector Different From Type 2

A Type 1 device is built to survive the punishing 10/350 µs waveform, the electrical signature of an actual lightning strike hitting a rod, a mast, or an overhead line. It sits at the TGBT, the origin of the installation, because that’s the only point where the full lightning current arrives before it disperses into branch circuits. Type 2 devices handle the 8/20 µs waveform, the shorter, less energetic surge from induced transients or switching events downstream. That difference isn’t academic. It changes the rating that matters: Type 1 is specified by Iimp (impulse current), Type 2 by In (nominal discharge current).

CharacteristicType 1Type 2
Waveform tested10/350 µs8/20 µs
Key ratingIimp (kA)In (kA)
Typical locationOrigin of installation (TGBT)Downstream distribution boards
Triggers requirementParatonnerre, aerial supply, Nk>25General surge exposure

When a site has a lightning protection system, Type 2 alone is insufficient because it can’t absorb the direct impulse current without failing. The standard approach cascades protection: Type 1 at the TGBT, Type 2 at sub-distribution boards, and Type 3 near sensitive terminal equipment, each stage catching what the one before it lets through.

Sizing a Type 1 Device: Iimp, Up, and Ifi Explained

Hands wiring surge protector terminals in electrical panel

Selection starts with the site’s lightning protection level (LPL), determined by a risk assessment. From there, Iimp minima scale with protection level: typical benchmarks run 12.5 kA, 18.75 kA, 25 kA, and 35 kA per pole. A building assessed at protection level II doesn’t have to stop at the bare minimum. If the site carries critical loads, data centers, medical equipment, industrial controls, specifying a 25 kA device instead of 18.75 kA buys real headroom against the next severe storm season.

Three more numbers decide whether a Type 1 device actually protects the equipment behind it:

  1. Iimp per pole. Match this to LPL first, then add margin for exposure and load criticality.
  2. Up (voltage protection level). This is the residual voltage that reaches downstream equipment. Lower Up means tighter protection, but it must still align with the withstand voltage of the gear it protects.
  3. Ifi (auto-extinction current). For spark-gap technologies, Ifi must exceed the site’s available short-circuit current (Icc), or the device keeps conducting after the lightning event ends instead of resetting.

Products also vary by pole count. Single-phase installations typically use 1P configurations; three-phase systems need 3P+N, with each pole carrying its own Iimp rating tested under NF EN 61643-11.

Pro Tip:Never specify Iimp alone in a procurement document. A device can meet the kA target and still fail if Ifi is lower than the panel’s Icc, so both numbers belong in the same line item on any RFQ.

For procurement, a working checklist looks like this: confirm site LPL, set minimum Iimp per pole, verify Ifi exceeds available Icc, check Up against equipment tolerance, and lock in pole count for the supply configuration.

Where the Regulations Require Type 1 Protection

Type 1 belongs at the origin of the installation, the TGBT, immediately downstream of the main disconnect. That placement matters because it’s the only point that sees the full lightning current before distribution splits it across circuits. When the building has an external lightning protection system, the SPD’s earth connection needs to tie into the same equipotential bonding network as the rod’s grounding conductor, not a separate, isolated earth.

The normative trail a specification should cite is short but specific: NF C 15-100 sets the baseline obligation, EN 61643-11 governs SPD testing and performance, EN 62305-2 covers risk assessment and dimensioning, and UTE C 15-443 details the practical application of Type 1/2/3 coordination.

Establishments receiving the public, classified industrial facilities, and high-rise buildings frequently carry lightning protection obligations that exceed general residential or light commercial rules, and a risk assessment often determines whether a paratonnerre and its associated SPDs are required rather than a blanket rule.

  • ERP (public-facing buildings): risk assessment usually decides the obligation, not building size alone
  • ICPE (classified industrial sites): sector-specific thresholds often apply on top of NF C 15-100
  • IGH (high-rise buildings): height and occupancy typically push requirements toward the complete EN 62305-2 method rather than the simplified UTE C17-108 approach

Where the assessment is ambiguous, the complete EN 62305-2 method gives a defensible number; the simplified UTE C17-108 approach works for lower-stakes sites where a full risk study isn’t proportionate to the exposure.

The Wiring Rules That Make or Break SPD Performance

A correctly rated Type 1 device still fails if the wiring around it is wrong. The most common installation error is a conductor loop that’s too long between the SPD, the protective earth, and the busbar it protects.

  1. Apply the 50 cm rule. Keep the total loop length connecting the SPD to line and earth under 50 cm; longer loops add impedance that lets voltage spikes through anyway.
  2. Size the earthing conductor for lightning current, not just fault current. Undersized bonding conductors are a frequent finding on retrofit inspections.
  3. Coordinate upstream fusing so the SPD doesn’t get disconnected by its own protective device before it can do its job.
  4. Mount close to the TGBT, not in a remote enclosure that forces long cable runs back to the busbar.

Pro Tip:If a retrofit can’t hit the 50 cm loop length because of panel layout, a dedicated sub enclosure mounted directly at the TGBT usually solves it faster than rerouting existing feeders.

Testing and Replacement: Reading the Warning Signs

A Type 1 SPD can look untouched after absorbing a major strike and still be electrically compromised. Visual inspection alone misses degraded residual voltage performance, which is why testing protocol matters as much as the hardware spec.

  • Check the mechanical status indicator on every scheduled inspection; a tripped flag means immediate replacement
  • Run a residual voltage test after any confirmed lightning event at the site, even without visible damage
  • Log every inspection date, indicator reading, and replacement in a maintenance record for insurance and compliance purposes
  • Set inspection frequency higher for sites in known high Nk zones, where repeated strikes are more likely over a device’s service life

Minimum Iimp baseline: most specifications for a standard protection level start at 12.5 kA per pole, a figure worth writing directly into replacement specifications so a swapped device doesn’t quietly downgrade protection.

How Indelec Approaches Type 1 Selection and Installation

Indelec has worked in lightning protection since 1955, running risk assessments, device selection, installation, and certification as a single continuous process rather than separate handoffs, often collaborating with industrial and commercial electrical and energy solutions specialists for comprehensive project delivery. Its R&D center keeps device selection tied to current standards instead of outdated rules of thumb.

  • Site risk assessment under EN 62305-2 or UTE C17-108, matched to actual LPL rather than a generic default
  • Device selection cross-checked against Iimp, Ifi, and Up requirements for the specific panel and load profile
  • Installation supervision to confirm the 50 cm rule and bonding are met on site, not just on paper
  • Certification documentation for compliance and insurance records
PointDetails
Turnkey processRisk assessment, device selection, installation, and certification handled as one continuous engagement.
Standards-first selectionDevices matched to EN 62305-2 protection levels rather than generic catalog defaults.

Why Numbers Beat Marketing Every Time

Every Type 1 specification argument eventually reduces to three figures: Iimp, Up, and Ifi against site Icc. The industry’s habit of leading with brand features instead of these numbers is backward, and it’s the reason so many installations pass a paper review and still underperform in the field.

Diagram showing comparison of surge protector ratings and site current

The bigger blind spot isn’t device selection at all. It’s wiring. A 35 kA-rated SPD connected with a meter-long conductor loop performs worse than a 12.5 kA device wired to the 50 cm rule, because impedance in that loop lets voltage through regardless of what the datasheet promises. Most specification failures trace back to installation discipline, not undersized hardware.

If there’s one priority to fix first, it’s this: stop treating the risk assessment as paperwork. An LPL calculated honestly, then matched to Iimp with margin for critical loads, prevents more failures than any single product choice downstream of it. Coordination between Type 1, 2, and 3 devices matters too, but it only works if the first stage was sized correctly to begin with.

— INDELEC

Get a Site-Specific Risk Assessment Before You Specify Anything

Choosing the right Iimp, Up, and Ifi values on paper only protects a building if the risk assessment behind them reflects the actual site, not a generic default pulled from a catalog. Indelec runs that assessment under EN 62305-2 or UTE C17-108, then carries the same team through device selection, installation supervision, and certification, so the numbers in the specification match what actually gets wired at the TGBT.

Indelec

That continuity matters most on ERP, ICPE, and IGH sites, where the obligation itself depends on a proper risk study rather than a blanket rule. Indelec’s lightning protection services cover exactly that path, from initial assessment through installation and compliance documentation. If your next project needs a Type 1 specification that will hold up under inspection, request a site risk assessment before the panel schedule gets finalized.

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