A surge arrester is a bit like an airbag for the electrical installation. Most of the time, you don’t need it. The day transient overvoltages arrive, you’re glad it’s there.
Yet, surge arrester selection remains a source of errors, especially when you’re torn between Type 1, Type 2 and Type 3. We still see panels protected “on paper”, but poorly coordinated, or with cables too long, so less effective.
In this guide, we clarify the role of each type, we link it to common cases (residential, small tertiary), then we move on to sizing criteria and installation points that change everything.
Type 1, Type 2, Type 3: understanding what protects what (and where)
Low voltage surge arresters are classified by type, according to tests and use (IEC 61643-11). Simply put, you can think of a logic of successive “barriers”, from most robust to finest.
- Type 1: it absorbs part of the energy associated with a lightning strike, especially when the risk of direct impact or incoming lightning current is real (for example presence of an LPS, overhead arrival, exposed buildings). Tested with a 10/350 µs wave, its key parameter is impulse current (Iimp).
- Type 2: it’s the “panel” surge arrester. It handles induced overvoltages, more frequent but less energetic. Tested with an 8/20 µs wave, we mainly look at nominal discharge current (In) and maximum discharge current (Imax), as well as protection level (Up).
- Type 3: it’s the finishing touch, closest to sensitive equipment. It’s used when you want to further reduce residual overvoltage (IT, TV, automation, boxes, etc.). Its usefulness depends heavily on cable lengths and equipment sensitivity.
To fix ideas, here’s a quick memo:
| Type of surge arrester | Usual location | Parameter to read first | Typical use |
|---|---|---|---|
| Type 1 | At the head of the installation | impulse current (Iimp) | Exposed sites, LPS, “hard” arrival |
| Type 2 | Main or sub-panel | nominal discharge current (In), maximum discharge current (Imax), protection level (Up) | Standard building protection |
| Type 3 | Near equipment | protection level (Up) | Fine equipment protection |
For a structured explanation by types and test classes, you can rely on the “reference” page of manufacturers, for example how to choose your surge arrester (types 1, 2, 3).
A good habit: choose the location and overvoltage scenario first, then select the type, not the other way around.
Starting from real risk and NF C 15-100 requirements (France, Belgium, Switzerland)
In real life, lightning protection begins with a realistic assessment of risk; you don’t equip an isolated house the same way as a small tertiary full of electronics. You don’t protect a site with a lightning rod like a pavilion in a low-storm area either. So, before choosing a reference, you must qualify the context by starting from real risk, notably via the keraunic level, lightning strike density and, for France, the AQ2 zone.
Simple questions that quickly guide the right choice
You save time with three questions:
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Does the site have a lightning rod, external lightning protection system (LPS) or equivalent constraints? If yes, a Type 1 protection device at the head often makes sense, even becomes mandatory in the presence of a lightning rod, because the lightning current can “enter” through networks.
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Is the power network overhead, long, or located in an exposed area? The more the environment favors overvoltages, the more a well-sized Type 2 becomes essential. In Switzerland, prevention information reminds of impact frequency and indirect effects, see data and measures on lightning (PLANAT).
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Do you have sensitive or expensive equipment? A boiler, a ventilation unit, a gate, a network rack, a home cinema—that changes the logic. In this case, a Type 3 near loads makes sense, especially if cable lengths are significant.
And on the standards side, what do we really look at?
In France, the NF C 15-100 standard frames electrical installation cases and implementation rules for electrical installation. To stay aligned with the spirit of NF C 15-100, we rely on summary documents, such as the NF C 15-100 practical guide (PDF), and on educational resources, such as when should you install a surge arrester?
In Belgium and French-speaking Switzerland, regulatory frameworks differ, but the method remains the same: identify exposure, choose coherent protection, then care for grounding. On our sites, it’s often that last point that makes the difference between “installed” and “effective”.
Sizing and installing without losing effectiveness: Up, Uc, cabling, coordination
Once the type is chosen, sizing a surge arrester or protection device depends on a few values, easy to read on a datasheet, but easy to misinterpret.
Parameters to read (and how to relate them to the field)
- Maximum continuous operating voltage (Uc): adapt it to the network (230 V single-phase, 400 V three-phase, TT, TN scheme, etc.). Wrong Uc, and the surge arrester ages too quickly.
- Up (protection level): the lower it is, the more you limit residual overvoltage. It’s a key number when protecting electronics.
- Iimp (Type 1), In/Imax (Type 2): these are discharge capacities, to be matched against the exposure scenario.
- Protection mode: depending on the earthing scheme and the distinction between common mode (between phase/neutral and earth) and differential mode (between phase and neutral), you don’t wire the same way (L N, N PE, etc.). Connection details and low voltage design rules are well summarized in surge arrester connection (Schneider guide).
The rule we forget too often: the connection length
A surge arrester can be excellent, but become mediocre if wires act like an “antenna”. Each centimeter adds inductance, hence overvoltage. The earth connection must be of good quality to effectively evacuate lightning current; otherwise, even a good close earth connection isn’t enough if connections are long. We aim for short, direct connections to earth, and good quality earth, otherwise the “real” Up climbs.
In the field, we use simple benchmarks, including recommended connection distance (often given at less than 50 cm) and the wiring order at the electrical panel. For a clear reminder, see how to install a surge arrester in the electrical panel.
Our cascading coordination method (without overcomplication)
We avoid complicated setups, but we stay rigorous for this protection device:
- We place the Type 2 surge arrester at the TGBT (it’s the most common base).
- We add a Type 1 surge arrester at the head if the site is exposed (LPS, at-risk arrival).
- We complete with Type 3 surge arresters as close as possible to sensitive loads, especially if circuits are long.
- We verify the associated disconnection device (circuit breaker or fuse), according to the manufacturer’s instructions.
- We also think about copper networks (telecom, RJ45), because an overvoltage can enter there, and this protection device must cover everything.
To move faster in study and control, we rely on the knowledge base, wiki and blog of lpsfr.com, then we centralize our choices and verifications in LPS Manager (multi-site monitoring, scoring, audits, weather alerts).
Conclusion
A good surge arrester isn’t just “Type 1, 2 or 3”. It’s a coordinated lightning protection device, adapted to the risk of the electrical installation, and installed with short connections and careful grounding. If you’re unsure, go back to the site (exposure, network arrival, sensitive equipment), then validate Uc, Up parameters and discharge capacities, to ensure the safety of these sensitive equipment. Lightning protection is a global strategy for the electrical installation. To supplement with demonstrations and field feedback, you can also follow the YouTube LPS channel.
