Type 1, Type 2, Type 3 Surge Arresters — Differences and Applications

Surge protectors, or SPDs (Surge Protective Devices), constitute the first level of defense against overvoltages caused by lightning or switching. However, not all surge protectors are created equal: the IEC 61643 standard defines three distinct types, each with a specific role in the protection chain. Understanding their differences is essential for designing effective and compliant protection.

What is a Surge Protector (SPD) according to IEC 61643?

A surge protection device (SPD) is a component designed to limit transient overvoltages and divert lightning currents. The IEC 61643-11 standard defines the performance, testing, and marking requirements for SPDs intended for low-voltage networks.

• Protection of electrical and electronic equipment against power surges
• Diverting lightning current to ground (controlled flow)
• Limitation of the residual voltage (Up) transmitted to downstream equipment
• Three categories defined by IEC 61643: Type 1, Type 2, Type 3

Furthermore, the choice of the right type of surge protector depends on its position in the electrical installation and the level of protection required.

Type 1 (T1) Surge Arrester — First Level of Protection

Type 1 surge protectors are the most robust. They are designed to protect installations against the direct effects of a lightning strike, particularly when a lightning rod is present on the building or when the power line is overhead.

• Location : at the head of the installation, at the main low-voltage distribution board (TGBT), downstream of the meter
• Standardized test : 10/350 µs current wave (Iimp) — representative of a direct lightning strike
• Pulse current (Iimp): typically 12.5 kA to 100 kA depending on the model
• Technology : gas spark gap or high-energy varistor
• Mandatory if the building is equipped with a lightning rod or if the line is overhead and unprotected.

Thus, Type 1 interrupts the main lightning current before it reaches equipment. However, on its own, it is not sufficient—the residual voltage Up of a Type 1 is generally too high to protect sensitive equipment.

Type 2 (T2) Surge Arrester — Protection against Induced Surges

Type 2 surge protectors are the most common in electrical installations. They primarily protect against overvoltages induced by nearby lightning strikes, network switching, and electromagnetic phenomena.

• Location : in a sub-distribution board, downstream of Type 1 or in the main distribution board if there is no lightning rod
• Standardized test : 8/20 µs current waveform (Imax) — representative of an induced overvoltage
• Maximum discharge current (Imax): typically 40 kA to 80 kA
• Nominal discharge current (In): typically 20 kA (IEC 61643 reference value)
• Technology : varistor (MOV) primarily

Therefore, Type 2 is the minimum level of protection recommended in any installation according to NF C 15-100, even in the absence of a lightning rod.

Type 3 (T3) Surge Arrester — Thin Protection at Equipment Output

Type 3 surge protectors offer precise protection for sensitive electronic equipment. Indeed, even after passing through a T1 and a T2, the residual voltage can still exceed the dielectric strength of some devices.

• Location : in the immediate vicinity of the equipment to be protected (surge protectors, dedicated boxes)
• Standardized test : combined wave 1.2/50 µs – 8/20 µs
• Residual protection voltage (Up): very low, generally < 1 kV
• Typical applications : computing, telecommunications, industrial automation, medical equipment
• Cannot be used alone — must be preceded by a T1 and/or T2

Coordination T1 + T2 + T3 — An Obligation according to IEC 62305-4

The coordination of protection levels is a critical aspect that is often overlooked. Furthermore, the IEC 62305-4 standard specifies the coordination requirements to ensure the effectiveness of the entire system.

• Minimum distance between T1 and T2: generally ≥ 10 m of cabling (otherwise a decoupler is required)
• Minimum distance between T2 and T3: generally ≥ 5 m of cabling
• If insufficient distance: use coordinated SPDs (T1+T2 in a single device)
• The residual protection voltage of each stage must be ≥ 80% of that of the following stage

Thus, each stage discharges a portion of the overvoltage current, progressively reducing the residual voltage to a level safe for the end equipment.

Surge protector vs. lightning rod — Two complementary protections

A common misconception is to oppose surge protectors and lightning rods. However, they address different threats and are strictly complementary.

• Lightning rod (IEC 62305-3): captures and dissipates the current from a direct impact on the structure
• Surge arrester (IEC 61643): protects against transient overvoltages induced on electrical networks
• A lightning strike 1 km away can induce overvoltages ≥ 10 kV on an unprotected power line
• A surge protector does not protect against a direct strike; a lightning rod does not protect against induced overvoltages

Therefore, full protection according to IEC 62305 systematically includes both levels of protection.

Criteria for Choosing a Lightning Arrester

• Type : T1, T2 or T3 depending on the position in the installation
• Iimp / Imax : impulse current adapted to lightning risk exposure
• Up : residual protection voltage — as low as possible, ≤ 1.5 kV for T2
• Uc : maximum continuous operating voltage — higher than the nominal network voltage
• In : nominal discharge current — 20 kA minimum for T2 in residential applications
• thermal disconnector — end-of-life safety for the surge protector

Grounding — An Essential Condition

A surge protector without effective grounding is useless, even dangerous. Therefore, the quality of the grounding connection directly affects the effectiveness of the surge protector.

• Earth resistance ≤ 10 Ω (IEC 62305-3 recommendation)
• Connection between the SPD and earth using conductors of suitable cross-section
• Ground stakes correctly installed and measured
• Equipotential Spark Gap between all the grounding points of the installation

Surge Arrester Monitoring with LPS Manager

Surge protectors have a limited lifespan. Each absorbed surge slightly degrades the varistor. However, LPS Manager allows you to monitor the status of each surge protector in the installation and anticipate replacements.

• Register of all surge protectors in the installation with references and installation dates
• Monitoring the status of the end-of-life indicator (control window)
• Periodic inspection and replacement reminders
• Integration with Strike Radar : verification alert after each detected impact
• Inspection reports including the condition of all SPDs

Frequently Asked Questions

What is the difference between Type 1 and Type 2 surge protectors?

Type 1 surge protectors are designed to protect against the direct effects of a lightning strike—they are tested with a 10/350 µs waveform representative of a real lightning strike. Type 2 protects against induced overvoltages—they are tested with a less energetic 8/20 µs waveform. Type 1 must be installed at the main distribution board (TGBT) if a lightning rod is present; Type 2 in sub-distribution boards.

Where should a Type 1 surge protector be installed?

The Type 1 surge protector must be installed at the main low-voltage distribution board (TGBT), downstream of the main circuit breaker (meter), before any branch circuits lead to sub-distribution boards. It is mandatory when the building is equipped with a lightning rod or when the power supply is overhead and not buried.

Is a Type 2 surge protector sufficient without a Type 1?

If the building is not equipped with a lightning rod and the power supply is underground (underground cable from the grid), a Type 2 surge protector may suffice for basic protection. However, if a lightning rod is present or the line is overhead, a Type 1 surge protector is mandatory in addition to a Type 2.

Can a Type 3 surge protector be used on its own?

No. The Type 3 surge protector is designed solely as supplementary precision protection. It cannot absorb high impulse currents and must be preceded by a T1 and/or T2 surge protector to dampen the bulk of the surge. Used alone, it would be destroyed during a significant overvoltage.

What is the lifespan of a surge protector?

The lifespan of a surge protector depends on the number and magnitude of surges it absorbs. Generally, the nominal lifespan is 10 to 15 years under normal conditions. However, after a significant lightning strike, the end-of-life indicator (monitoring window) may signal the need for immediate replacement.

Does a surge protector protect against a direct lightning strike?

No. A surge protector does not protect against a direct lightning strike on the structure or cables. Protection against direct strikes is provided by a lightning rod (IEC 62305-3). A surge protector only protects against transient overvoltages induced on the electrical network by nearby lightning strikes.

Does NF C 15-100 require a Type 2 surge protector?

Yes. The NF C 15-100 standard (2015 edition) mandates the installation of a Type 2 surge protector in the main electrical panel of all new or renovated residential electrical installations, unless the power supply comes from an underground network in a low lightning density zone. This is a regulatory requirement in France for new constructions.