Beyond Unit Price: How to Compare SPD Quotations from Different Suppliers

• Why unit price is the wrong starting point
• The fields that make SPD quotations comparable
• The “low price, non-comparable” traps
• How to run the comparison in four steps
• FAQ
• Get a specification-by-specification comparison of your current quotation

CRESIN · Surge protection fundamentals

Three suppliers have quoted you a Type 2 surge protective device (SPD). The unit prices differ by a factor of two or three. Which quotation should win the order?

If the decision starts from price, it starts from the wrong end. An SPD quotation is a list of specifications, and a price only becomes meaningful once those specifications are comparable. A cheaper quotation is usually not a cheaper product; it is a product whose specification has not yet been compared.

This guide does two things. First, it breaks an SPD quotation into the fields that must match before price is discussed: SPD type, Uc, Up, In/Imax, Iimp, the standard edition and its test report, thermal tripping protection, remote status signaling, backup protection, enclosure, MOQ, lead time, and warranty and replacement terms. Second, it shows the typical “low price, non-comparable” traps and gives you a downloadable comparison matrix to run the same fields against every supplier.

This article deliberately quotes no prices. At the quotation-comparison stage, the only number that matters is the specification gap — and that gap has to be closed before a price can be judged.

Why unit price is the wrong starting point

“Type 2 SPD” is not a product class; it is a test class. Two devices that both pass Type 2 testing can differ in Uc from 275 V to 440 V, in In from 5 kA to 40 kA, in Imax from 20 kA to 100 kA, in enclosure and mounting, in whether a thermal tripping device is fitted, and in whether a test report exists at all. Comparing their unit prices is like comparing a 1.5-ton van with a 12-ton truck because both are called vehicles.

Procurement usually fails in one of two ways. Either the buyer compares prices on nominally identical models and takes the lowest one, or the buyer accepts a lower-specification device at a lower price and discovers the gap only at inspection, at a factory audit, or after a surge event. Both failures are visible in the quotation before any money changes hands — if you know which fields to read.

The field-by-field method below is the one we apply when we review project requirements against our own SPD ranges: fix the site parameters first, demand the same specification fields from every supplier, and only then compare price.

The fields that make SPD quotations comparable

Before comparing prices, you need every supplier to answer the same questions. Each field below changes the price, and each can make two quotations non-comparable even when both state “IEC 61643 compliant”. Table 3 is the risk map — each field, why it matters, the risk if ignored, and what to demand. The downloadable comparison matrix at the end of the article is the working template.

Table 3. Quote fields — risk map (what to check before comparing price)

SPD Type (Type 1 / Type 2 / Type 3)

The Type defines where the SPD may be installed and which test regime it passed. Type 1 devices are tested with the 10/350 µs impulse current (Iimp) and are used at the main incoming distribution where direct lightning strikes are a risk. Type 2 devices are tested with the 8/20 µs current wave (In/Imax) and are used in sub-distribution and terminal boards. Type 3 devices protect sensitive terminal equipment at the point of use.

In a quotation, a Type 2 device cannot replace a Type 1 requirement at any price. Check the Type on the datasheet and in the test report, not only on the sales sheet. See our AC power SPD range for the Type 1 and Type 2 configurations typically supplied for distribution boards.

Uc — maximum continuous operating voltage

Uc is the highest continuous voltage (RMS for AC, DC for DC systems) at which the SPD can be connected. For a 230/400 V system, quotations commonly list Uc = 275 V, 320 V, 385 V or 440 V. These values are not interchangeable: a 320 V device is not comparable with a 385 V device, and a Uc below the actual continuous operating conditions — including voltage tolerance and temporary overvoltages (TOV) — is a common cause of premature SPD aging and nuisance disconnection.

Compare Uc at the same value, against the same system voltage and earthing arrangement (TN-S, TN-C-S, TT, IT). If a supplier cannot state Uc, treat the quotation as incomplete.

Up — voltage protection level

Up is the voltage protection level: the voltage the SPD lets through under the specified test conditions. All else being equal, a lower Up protects downstream equipment better. The catch is that Up is only meaningful together with the test current at which it is measured, and with the same Uc. A modest Up quoted at a low test current is not comparable with a standard-compliant Up measured at In.

For coordination, the Up must fit the impulse withstand voltage (Uw) of the protected equipment; IEC 61643-12 sets out the selection and application rules, including SPD-to-equipment coordination. Demand the Up declared per the standard at In, not a best-case figure.

In and Imax — nominal and maximum discharge current

In (8/20 µs) is the nominal discharge current that the SPD must withstand a defined number of times under test. Imax (8/20 µs) is the maximum single discharge current it can withstand once. In is the field to compare; Imax is the figure that sells. A quotation that leads with a large Imax while the In is small is a classic presentation trick — read In first.

Record both values in the matrix and cross-check them against the test report.

Iimp — impulse current (Type 1 only)

Iimp is the 10/350 µs impulse current that a Type 1 SPD must handle. Values of 12.5 kA, 25 kA and 50 kA per pole are common, and the required rating follows from the lightning risk assessment of the site (per the IEC 62305 series). If your site requires Type 1 protection and a quotation omits Iimp or shows only an 8/20 µs figure, the quotation does not deliver Type 1 protection.

Standard, edition and test report

The IEC 61643 series was restructured. IEC 61643-01:2024 now contains the common requirements for all SPDs, and IEC 61643-11:2025 (second edition) covers SPDs connected to AC low-voltage power systems, cancelling and replacing the first edition of 2011. Regionally, GB/T 18802.11-2020 applies in China and UL 1449 in North America. Photovoltaic DC circuits are covered by IEC 61643-31; signal and data lines by IEC 61643-21.

What to demand in a quotation: the standard name and its edition, plus a test report from an accredited laboratory with report number and date. “IEC 61643-11 compliant” without an edition or a report is a marketing sentence, not a specification. For DC and PV applications, the same discipline applies to our DC power SPD range.

Thermal tripping protection and failure indication

A varistor-based SPD that reaches end of life should be thermally disconnected from the line rather than fail short-circuit and create a fire hazard. Check that the quotation states the disconnection behaviour and the failure indication — a local status indicator, and a remote signal contact where the project needs it. If the quotation is silent on end-of-life behaviour, ask.

Remote status signaling

If the project requires remote monitoring of SPD status, the quotation must include the potential-free remote contact. Retrofitting signaling later costs more than specifying it. Note that a red/green local status indicator is not remote signaling; they are different features.

Backup protection and short-circuit withstand

An SPD must be coordinated with the upstream overcurrent protective device (fuse or circuit breaker). The quotation should state the maximum backup protection and the resulting short-circuit withstand of the SPD. Without this, the SPD may pass its surge tests and still fail the installation requirement, leaving a hole in the protection coordination study.

Enclosure, IP rating and mounting

Record the housing material and flame class, the degree of protection (for example IP20 for indoor DIN-rail mounting, IP65 for outdoor enclosures), the mounting method and the module footprint. An IP20 quotation is not comparable with an IP65 one for an outdoor cabinet, and a pluggable module design changes the cost of replacement.

MOQ

The minimum order quantity changes the economics of a quotation even when the unit price is low. Compare unit price at the same quantity, and record whether the MOQ applies per model or per order.

Lead time

Project schedules are part of the quotation. Record the lead time and the point from which it starts — order confirmation, sample approval or payment.

Warranty and replacement policy

Record the warranty term, what it covers (the complete unit or the protection module), whether a surge event that ends the SPD’s service life triggers replacement terms, and the replacement mechanism. Warranty wording is where low-price quotations typically hide cost: a short warranty on a disposable unit is a different product from a longer warranty on a replaceable module with defined terms.

The “low price, non-comparable” traps

The traps below are what produce a cheap-looking quotation. Each one is verifiable from the quotation itself, which is the point of the field-by-field method.

Table 4. Ten typical “low price, non-comparable” traps

How to run the comparison in four steps

Step 1 — Fix the site parameters first. Record the system voltage and earthing arrangement, the lightning risk assessment (per IEC 62305), the installation location (Type 1 at the incoming point, Type 2 downstream, Type 3 at the terminal), and the impulse withstand category of the protected equipment. These determine the target values of Type, Uc, Up, In and Iimp against which every quotation is measured.

Step 2 — Send the same blank matrix to every supplier. Use the downloadable comparison matrix at the end of this article. Ask each supplier to fill every field and attach the test report. No blanks allowed: a quotation with empty fields is a quotation you cannot compare.

Step 3 — Verify the reports. Check the standard and edition, the accredited laboratory, the report date and the model number against the quotation. A report that does not match the quoted model is no evidence at all.

Step 4 — Compare fields, then price. Only when the fields are equivalent — or the differences are priced and justified — does unit price become a decision variable. Score the matrix, then negotiate.

FAQ

What is the difference between In and Imax in an SPD quotation?

In (8/20 µs) is the nominal discharge current the SPD must withstand repeatedly under test; Imax (8/20 µs) is the maximum single discharge current. Compare In first — Imax alone is a presentation figure.

Does a lower Up always mean a better SPD?

All else being equal, yes. But Up is only meaningful together with the test current at which it is measured and the same Uc. A low Up quoted at a low test current is not comparable with a standard-compliant Up at In.

Which standard should an SPD quotation reference?

For AC low-voltage power systems, IEC 61643-11 (second edition, 2025) together with IEC 61643-01:2024; in China, GB/T 18802.11-2020; in North America, UL 1449. Photovoltaic DC circuits use IEC 61643-31, and signal and data lines use IEC 61643-21. Demand the edition and the test report, not the standard name alone.

Why does one supplier’s quotation not include Iimp?

Because Iimp applies only to Type 1 SPDs. If the site requires Type 1 protection, a quotation without Iimp does not meet the requirement. If the quotation is Type 2, Iimp is correctly absent — check the Type against the site requirement instead. For signal and data lines the applicable standard is IEC 61643-21; see our Signal & Data SPD range.

How do I verify an SPD quotation’s test report?

Check the standard and edition, the issuing laboratory, the report date, and that the model number on the report matches the quoted model. If any of these do not match, ask for a corrected report before comparing prices.

What does Uc tell me in a quotation?

Uc is the maximum continuous voltage the SPD can be connected to. It must fit the system voltage and earthing arrangement of the installation. A Uc too low for the grid conditions causes premature aging and nuisance disconnection. If you need help confirming the correct Uc for your application, contact us for technical support and product selection assistance.

Get a specification-by-specification comparison of your current quotation

The comparison matrix in this article lets you run the same fields against every supplier, including the one whose quote you already have. When you are ready to check where your current quotation stands, send your current quote to our engineering team for a specification-by-specification comparison. You will receive a field-by-field gap analysis against your site parameters — no price promises, no delivery promises, just the fields you can verify and negotiate on.

About the publisher: this guide was prepared by the engineering and sales teams of Cresin (Shandong Cresin Electric Co., Ltd.), a surge protective device manufacturer.