Tip 1, Tip 2 ve Tip 3 SPD: Kapsamlı Bir Seçim Karar Ağacı

Selecting the wrong surge protective device type is one of the more common and more expensive specification errors in low-voltage installations. The device may work, the installation may pass inspection, and the system will still be under-protected for the actual risk it faces — because Type 1, Type 2, and Type 3 devices are not ranked versions of the same thing. They answer different questions.

This guide sets out how to choose between the three types. It works as a decision tree: start from the installation’s lightning protection zone and the origin of the threat, arrive at the device type, then confirm the parameters that must match. Detailed comparison of Type 1 and Type 2 characteristics is covered separately, as is the parameter-by-parameter sizing of Type 2 devices for low-voltage distribution.

İçindekiler

First: What Each Type Actually Does

The three types are distinguished by the test waveform they are certified against, and that test defines what they can do.

Type 1 (Iimp) is tested with a current impulse representing a partial direct lightning current — the kind that flows when a building’s air termination or external conductors are struck. It is defined by Iimp, in kA, representing the partial current the device can withstand at 100 ms.

Type 2 is tested with a current or voltage impulse representing induced effects: nearby lightning discharges, switching transients in the power system, and coupling from neighbouring installations. It is defined by a combination of Imax, In, Isc, and Up depending on the device topology.

Type 3 is tested with a combined waveform representing induced effects at a lower energy level, intended for protection of specific downstream equipment rather than whole installations. It is defined by Uoc, the open-circuit voltage of the test.

The practical consequence: a Type 2 device cannot substitute for a Type 1 where a direct strike is possible, because it has never been tested for that current profile. Equally, installing Type 1 everywhere is not automatically better — the test category exists to match the device to the actual threat.

The Decision Tree

Three questions determine the device type, in order:

• What is the origin of the surge? Direct lightning strike or external LPS currents → Type 1 territory. Induced lightning effects or switching transients → Type 2 territory. Sensitive equipment at the end of a longer run → Type 3 territory.
• What is the lightning protection zone (LPZ) boundary? The zone determines the required device class per IEC 61643-11.
• What equipment is downstream, and what is its withstand voltage? This sets Up, not the device type.

If the first question cannot be answered, the protection cannot be specified correctly. This is the step most often skipped.

Step 1: Identify the Threat

Direct strike on the building or its LPS

When lightning can strike the structure itself, or external conductors such as a mast or air termination, the surge that reaches the installation is a partial lightning current. This is the Type 1 case. It is the only category tested for this profile.

Induced effects from a nearby strike

The far more common case. The lightning channel does not touch the building; it induces a transient on nearby conductors, which couples into the installation through mains wiring, external cables, or long internal runs. Type 2 addresses this.

Switching transients from the power system

Energising loads, capacitor bank switching, transformer inrush, and the operation of devices upstream all generate transient overvoltage on the distribution network. These are entirely unrelated to lightning and are handled by Type 2 devices.

Long cable runs to sensitive equipment

Where a device sits at the end of a long external or internal cable run, induced effects arrive attenuated in energy but still capable of damaging sensitive equipment. A Type 3 device, installed close to that equipment, addresses this specific case.

Step 2: Establish the Lightning Protection Zone

Per IEC 61643-11, a building’s lightning protection system divides it into lightning protection zones. The zone structure follows from the presence of external LPS elements and the building’s construction.

• LPZ 0 — the volume where lightning direct effects are possible; the exterior of the building before the LPS intercepts.
• LPZ 1 — the volume where direct effects are no longer possible but induced effects may occur; roughly the volume enclosed by the LPS.
• LPZ 2 and beyond — volumes with progressively lower induced-effect risk as distance from the boundary increases.

The SPD requirement per zone follows a recognised pattern: Type 1 devices at the boundary from LPZ 0 to LPZ 1, Type 2 devices at the boundary from LPZ 1 to LPZ 2, and Type 3 devices at the protected equipment where distance from the LPZ 2 boundary exceeds 10 metres of cable or 20 metres of conduit routing.

That last distance criterion is where Type 3 earns its place. A Type 2 device at the main distribution board does not protect equipment 25 metres of cable downstream from induced effects arriving on that cable — the transient is generated along the run itself.

Step 3: Choose the Device Type

Two rows deserve emphasis. The last is the honest answer for a site with no lightning protection system and frequent strikes: no SPD compensates for the absence of an LPS, and specifying higher-category devices is not a substitute for air termination and down-conductors.

The fourth row applies to nearly every photovoltaic installation. PV DC cables run outdoors for substantial distances, which places them squarely in the induced-effects case and makes Type 2 PV-rated devices standard on the DC side.

Type 1 in Practice

Type 1 devices sit at the LPZ 0/1 boundary, which in practice means the incoming mains entry point, close to the building’s main switchboard and before any significant cable run. They are normally installed alongside Type 2 devices rather than instead of them.

Critical specification points: Iimp must be selected against the likely partial current, typically 25 kA for residential and small commercial buildings in high-risk regions, higher where the LPS is minimal relative to the building size. The device must be capable of withstanding the current long enough for the LPS down-conductors to take the majority of the energy to earth.

GA&DA supplies Type 1 SPDs in the GA&DA GD-series range, including the G2035MT and G2050MT configurations for distribution applications.

Type 2 in Practice

Type 2 is the default device type for low-voltage installations, and most projects need nothing else. It is installed at the LPZ 1/2 boundary — typically the main distribution board — and covers both induced lightning effects and switching transients across the whole installation.

Specification depends on topology:

• Fixed limit voltage (Type 2a) — uses voltage-limiting devices such as MOVs or spark gaps. Continuous voltage follow-through is a consideration with MOVs.
• Combination Type 2b — series filter plus limiting element, giving a lower residual voltage and a wider application range.
• Combination Type 2c — incorporates a current-limiting element to clear the line in case of a series fault, useful where sustained overvoltage is possible.

Key parameters: Yukarı (maximum protection voltage) must sit below the withstand voltage of downstream equipment; Uc must equal or exceed the nominal system voltage; İçinde veya Imax must be coordinated with the backup protection. Detailed sizing guidance for these parameters is covered in the dedicated Type 2 selection article.

GA&DA’s Type 2 range spans the GA&DA GD-MT, GD-DZ, and GD-XZ series across pole counts and current ratings, with DC and PV variants available for photovoltaic applications.

Type 3 in Practice

Type 3 is the least understood and most frequently misused of the three. It is not a weaker Type 2; it is a different test profile for a specific position in the installation.

Its purpose is protecting specific equipment against induced effects arriving along a long cable run. The measured parameter is Uoc, the voltage the device produces when disconnected. Uoc must be compared against the equipment’s withstand voltage — a Type 3 device with a Uoc above the equipment’s rating provides no protection regardless of how well it is installed.

Typical Type 3 positions: at the inlet of sensitive equipment, at the final sub-distribution board serving an IT or process load, or on individual circuits leaving the main board for long runs.

Two practical notes. First, Type 3 devices must not be installed as the sole protection for a distribution board. Second, because Uoc is the reference parameter, specifying Type 3 by a current rating such as “20 A” is meaningless — the comparison that matters is Uoc against equipment withstand voltage.

Confirming the Parameters

Once the type is chosen, four parameters must be confirmed against the installation:

• Uc — maximum continuous working voltage. Must equal or exceed the nominal voltage of the circuit. For a 230/400 V system, Uc of 275 V (1P+N) or 400 V (3P+N) is typical.
• Yukarı — maximum protection voltage. Must be below the withstand voltage of everything downstream.
• In / Imax / Iimp — discharge current or current handling capacity, selected against available fault current and the required protection level, then coordinated with the backup fuse or breaker.
• Direk düzeni — must match the circuit. For 3P+N systems, 4P devices; for TT single-phase, 1P+N; for a neutral-carrying system with switched and unswitched conductors, the arrangement must suit the earthing scheme.

Backup protection coordination deserves particular attention. A Type 2 device that fails short-circuit at end of life must be cleared by its backup device. This requires the available fault current at the installation point to fall within the device’s specified Imax/Isc range and the backup fuse to be correctly rated. Specifying Imax below the actual prospective fault current removes the manufacturer’s coordination guarantee.

Where Combinations Are Required

In practice, most installations need more than one type:

• Type 1 + Type 2 — the standard arrangement for any building with an external LPS. Type 1 handles direct currents at the LPZ 0/1 boundary; Type 2 handles induced effects downstream. Either alone leaves a gap.
• Type 2 + Type 3 — Type 2 at the distribution board, Type 3 at sensitive equipment more than 10 metres of cable away.
• Type 1 + Type 2 + Type 3 — complete protection for a building with an LPS and long cable runs to sensitive loads.
• AC and DC separately — AC SPDs at the mains board and DC SPDs on the PV side. A DC-rated device is required on the DC side because arc interruption behaves differently without voltage zero crossings.

Common Selection Errors

• Using Type 2 where Type 1 is required — the device is never tested for partial lightning currents.
• Specifying Type 3 by current rating — Uoc is the meaningful parameter; without checking it, protection cannot be assumed.
• Using Type 1 as “better than Type 2” — Type 1 does not replace Type 2. Induced effects and switching transients occur regardless of the LPS.
• Up above equipment withstand voltage — a common result of selecting on In or Imax alone, which says nothing about clamping performance.
• No backup coordination — without a correctly rated backup device, a failed SPD becomes an unresolved short circuit.
• Wrong pole configuration — a 2P device on a 3P+N system leaves conductors unprotected.
• AC device on a DC circuit — DC arcs do not self-extinguish at a current zero; arc-quenching capability differs fundamentally.
• Skipping the threat assessment — specifying before establishing whether direct strikes are possible at the site is the root cause of most of the above.

Related GA&DA Products

GA&DA manufactures Type 1, Type 2, and Type 3 surge protective devices across AC and DC applications, including PV-specific models for photovoltaic systems and signal and network protection variants. See the full aşırı gerilim koruma cihazları range, or review related technical guidance on surge current capacity and response time and DC circuit behaviour.