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Views: 0 Author: YNQT Technical Team Publish Time: 2026-09-02 Origin: Site
An SPD datasheet should answer one practical question:
Is this exact surge protective device suitable for the electrical system, installation point, connected equipment, and project requirements?
The answer cannot be found in the largest kA value alone. A high Imax does not correct an unsuitable Uc, excessive Up, wrong protection mode, insufficient short-circuit rating, or unsupported compliance claim.
This guide shows engineers, system integrators, and B2B buyers how to use an SPD datasheet as a technical decision tool. It covers the key parameters Uc, Up, In, Imax, and Iimp, then applies them to actual product data and supplier-document checks.
Scope: This guide focuses on low-voltage power SPDs in IEC-based applications. Final selection must follow the applicable local standard, system study, project specification, and manufacturer instructions.
Check these items before comparing prices or headline surge ratings.
Check | Decision question | Red flag |
|---|---|---|
Exact model | Does the datasheet include the full suffix and revision? | Only a product family is identified |
Application | Is the SPD for AC, PV DC, other DC, or signal circuits? | The application or product standard is unclear |
SPD type | Is it Type 1, Type 2, Type 3, or a combined type? | The type does not match the installation role |
System and modes | Do voltage, earthing, poles, and L-N/L-PE/N-PE modes match? | The connection diagram does not match the system |
Uc or Ucpv | Can the declared voltage be continuously applied? | The value is below the maximum applied voltage |
Up | Is the protection level suitable for the equipment? | Up is missing or shown for the wrong mode |
Surge current | Are In, Imax, and Iimp stated with waveforms and rating basis? | Per-mode and total values are mixed |
Fault coordination | Are Isccr and backup protection declared? | The fault-current condition is missing |
Evidence | Can the exact model be matched to a certificate or test report? | The document only says “complies with” |
If the installation location, electrical system, or required SPD category has not yet been defined, start with our complete surge protection device selection guide for electrical engineers and buyers before comparing individual datasheets.
Do not start with Imax. First confirm whether the datasheet covers the intended system.
As of 2026, low-voltage AC SPDs are covered by IEC 61643-11:2025, used with IEC 61643-01:2024. PV DC SPDs use IEC 61643-31:2018, while other low-voltage DC SPDs use IEC 61643-41:2025. Verify the relevant EN or national adoption for the target market.
The SPD type identifies a test duty and system role, not a simple quality level.
SPD type | Main test quantity | What it helps evaluate |
|---|---|---|
Type 1 | Iimp, 10/350 µs | Lightning-current duty |
Type 2 | In and Imax, 8/20 µs | Distribution-level surge duty |
Type 3 | Uoc combination-wave data | Fine protection near equipment |
Type 1+2 or Type 2+3 | Combined declarations | Performance under more than one test class |
If the project team has not yet determined which protection type belongs at the service entrance or downstream distribution panel, review the differences between Type 1 and Type 2 SPDs before evaluating current ratings.
Also confirm the exact protection modes. A 3+1 device and a 4+0 device may have different internal connections, protection levels, and total current declarations even when they belong to the same series.
Parameter | Meaning | Selection question |
|---|---|---|
Uc | Maximum continuous operating voltage for the specified mode | Can the SPD remain connected under the maximum system voltage? |
Up | Declared voltage protection level under defined impulse tests | Is it coordinated with the equipment withstand requirement? |
In | Nominal discharge current for the applicable 8/20 µs test sequence | Does it meet the required Type 2 duty? |
Imax | Maximum discharge current declared for the applicable 8/20 µs duty | Is it sufficient on the same mode and rating basis? |
Iimp | Impulse discharge current for Type 1 testing at 10/350 µs | Is the required lightning-current duty declared? |
Uc should be checked against the voltage applied to each protection mode, not only the nominal system label. Earthing arrangement, supply tolerance, and temporary overvoltage conditions also matter.
Within the LDSP1s-C40 Type 2 family, In and Imax remain constant while Uc and Up change:
Model | Uc | In | Imax | Up |
|---|---|---|---|---|
LDSP1s-C40-275 | 275 Vac | 20 kA | 40 kA | ≤1.5 kV |
LDSP1s-C40-320 | 320 Vac | 20 kA | 40 kA | ≤1.6 kV |
LDSP1s-C40-385 | 385 Vac | 20 kA | 40 kA | ≤1.8 kV |
LDSP1s-C40-440 | 440 Vac | 20 kA | 40 kA | ≤2.0 kV |
This does not mean the lowest Uc is always correct. It shows why a higher-Uc variant is not automatically an equivalent replacement: voltage compatibility and protection level must be reviewed together.
Up is also not the exact voltage that will reach the equipment. Connection conductors add inductive voltage, so the installed protection level can be higher than the datasheet value. Short connections and correct SPD coordination remain essential.
The LDSP1s7-275 Type 1+2 data lists Iimp of 7 kA at 10/350 µs and Imax of 50 kA at 8/20 µs. The 7 kA value is not “weaker” because the waveforms and test duties are different.
Before comparing current values, confirm:
SPD type and waveform
Protection mode
Per-pole, per-mode, or total basis
Exact model suffix
Applicable standard and test evidence
Two Type 2 AC series at the same 275 Vac Uc illustrate the problem:
Product family | In | Imax | Up | Isccr | Maximum backup fuse |
|---|---|---|---|---|---|
LDSP1s-C40-275 | 20 kA | 40 kA | ≤1.5 kV | 25 kA | 63 A gG |
LDSP1s-B60-275 | 30 kA | 60 kA | ≤1.8 kV | 25 kA | 100 A gG |
The B60 has higher In and Imax, but the C40 has the lower declared Up. Therefore:
A project requiring Up ≤1.5 kV, In ≥20 kA, and Imax ≥40 kA may favor the C40 data set.
A project requiring In ≥30 kA and Imax ≥60 kA while allowing Up ≤1.8 kV may favor the B60 data set.
Neither series is universally better. The correct SPD is the one that meets the complete project requirement.
Uc describes continuous operation; Ut describes a declared temporary overvoltage condition with a duration and behavior.
For the LDSP1s-C40-275, the catalog lists 335 Vac for 5 seconds with tolerance and 440 Vac for 120 minutes with disconnection. These values must not be compared without their time and outcome.
In the LDSP1s-C40-275 +0 configurations, the catalog lists Imax total from 40 kA for /1+0 to 160 kA for /4+0.
This does not make the four-element version four times better. It shows why a total rating must not be compared with another supplier’s per-mode value.
The SPD must be coordinated with the prospective short-circuit current and the manufacturer’s tested backup-protection conditions.
“Maximum backup fuse” is an upper declared condition, not an automatic fuse recommendation for every installation.
Check terminal capacity, mounting, operating temperature, IP rating, status indication, replaceable modules, and remote contacts.
These values can determine enclosure suitability, maintenance requirements, and technical-submittal acceptance.
A standard number on a datasheet is not complete proof of compliance. Request a document chain for the exact ordered model.
Document | What to verify |
|---|---|
Datasheet | Model suffix, revision, modes, units, waveforms, and ratings |
Certificate | Standard edition, issuing body, validity, and covered models |
Test evidence | Tested configuration, declared values, laboratory, and report number |
Installation instructions | Wiring, backup protection, terminals, torque, and safety limits |
Product label and drawing | Agreement with the datasheet and quotation |
For due diligence covering manufacturing capability, documentation consistency, certification, quality control, and B2B sourcing risk, see how to compare SPD manufacturers.
Stop the approval process when units conflict, waveforms are missing, per-mode and total ratings are mixed, or the certificate cannot be matched to the exact model.
Confirm the application, system voltage, earthing arrangement, installation point, SPD type, and exact model before comparing Uc, Up, or surge-current values.
No. Imax does not confirm Uc, Up, TOV behavior, protection mode, or fault coordination. Compare it only under the same waveform and rating basis.
No. A datasheet is a manufacturer-controlled technical declaration. Project approval may also require a current certificate, test report, and installation instructions covering the ordered model.
An SPD datasheet should be used as a decision record, not a list of numbers. A defensible evaluation follows this sequence:
Confirm the application, system, installation point, and exact model.
Check Uc or Ucpv and TOV behavior.
Coordinate Up with the equipment and installed protection level.
Compare In, Imax, Iimp, or Uoc on the correct test basis.
Verify protection modes, total ratings, Isccr, and backup protection.
Match the declared values to current supplier evidence.
The best SPD is not the product with the largest headline rating. It is the product whose complete datasheet can be matched to the electrical system, protection objective, installation conditions, and verifiable technical documentation.
