SPD Factory Audit Checklist: 10 Items to Verify Before Approving a Supplier

A certificate confirms one sample passed a test once. An SPD factory audit checklist confirms the factory producing your order actually runs the processes needed to deliver that standard on every batch. The ten items below apply equally to in-person visits and remote documentary audits.

Quick Answer

This SPD factory audit checklist covers: test reports, MOV sourcing, thermal disconnector verification, soldering process, test equipment, ESD control, batch traceability, AQL inspection, factory qualification documents, and golden sample policy. Items 3, 4, and 6 need physical inspection; the rest can be audited remotely.

1. IEC Test Reports — Originals, Not Scans

A certificate confirms a declaration was made; the test report is the evidence — request the original, not a scan. Confirm reports are issued by an accredited third-party lab (CNAS, DAkkS, UKAS), cover the exact model and protection mode (L-N, L-PE, N-PE) being ordered, and reference the current IEC 61643-11:2011+A1:2017 edition. In-house lab reports don't meet third-party verification requirements for most B2B procurement standards.

Request: full test report PDF with lab accreditation number, results for all applicable clauses, and the specific test class (Type 1/2/3, Imax, In).

2. MOV Sourcing and Incoming Inspection

The MOV is the primary protection element in most SPDs — batch-to-batch variation in varistor voltage directly affects clamping performance and end-of-life behaviour. Confirm whether MOVs are made in-house or sourced externally, whether 100% parametric testing (V₁mA, clamping voltage) is done on incoming batches, and whether batch traceability links finished SPD serial numbers back to MOV lots. For OEM orders, the MOV supply chain is part of your product liability.

Request: MOV supplier documentation (or in-house process summary) and incoming inspection sample records.

3. Thermal Disconnection Device — Verified, Not Assumed

The thermal disconnector is the primary safety mechanism that stops an end-of-life MOV from causing a fire — this item needs physical inspection of a sample unit, not documentation alone. Confirm every model includes one, whether it's integrated into the MOV or a separate component, its rated operating temperature, and whether it reliably triggers the fault indicator.

Request: cross-section or exploded diagram showing disconnector placement, plus type test activation temperature and response time records.

4. Soldering Process and Workmanship Standards

Cold solder joints are a common cause of field failures that have nothing to do with surge events — and they often pass a room-temperature functional test before failing under real operating conditions. Confirm the soldering process (wave, reflow, or manual), whether it's controlled by documented temperature profiles or operator qualification records, and what workmanship standard applies — IPC-A-610 is the most widely used reference.

Request: reflow profile or process spec, plus in-process inspection records.

5. Ageing and Endurance Test Equipment

A type test confirms the design meets the standard; a production test confirms the actual units leaving the factory match it — suppliers who only do the former can't give meaningful batch-level assurance. Confirm the factory has calibrated 8/20 µs surge generators traceable to national standards, and what percentage of production units get electrical testing before shipment (100% continuity and functional testing at rated voltage should be standard).

Request: test equipment list with calibration status, and a description of production testing scope.

6. ESD Control and Handling Procedures

ESD damage is latent — a device passes functional test but fails prematurely in service, and there's no way to catch it after the fact. Confirm the production area is an ESD-protected area (EPA), operators use grounded wrist straps, sensitive components are stored in ESD-safe packaging, and ESD equipment is tested regularly with records.

Request: ESD control procedure document and wrist strap testing records. On an in-person visit, check for EPA signage and grounding stations in actual use.

7. Serial Number and Batch Traceability

Without traceability, a field failure can't be root-caused and affected units can't be identified for recall — for OEM products carrying your brand, that turns one bad batch into a full-production exposure. Confirm finished units carry a serial number or date code linking back to MOV batch, PCB assembly batch, test results, and inspection records, and how long those records are retained.

Request: example production batch record (redacted if needed) and the record retention policy.

8. Pre-Shipment Inspection Records and AQL Standard

A supplier's willingness to permit third-party inspection and share their own outgoing QC records is a reliable proxy for how confident they actually are in their process. Confirm the AQL level applied (1.0/1.5 is appropriate for safety-critical SPDs, 2.5 is the industrial-component minimum) and whether third-party PSI by SGS, Bureau Veritas, or Intertek is permitted.

Request: most recent OQC inspection report and written confirmation that third-party PSI is permitted.

9. Factory Qualification Documents

The entity names on the business licence, ISO certificate, CE declaration, and test reports should all match — a mismatch can mean the certificates belong to a related company, not the factory actually producing your goods. Confirm current ISO 9001 certification, valid export/customs registration for your market, and that the Declaration of Conformity cites the correct EU directives (Low Voltage 2014/35/EU, EMC 2014/30/EU).

Request: ISO 9001 certificate (front + scope page), business registration, and the Declaration of Conformity.

10. Golden Sample Policy and Retention

The golden sample is the physical contract for what "correct" looks like — without one on file, disputes about colour, finish, or component substitution have no objective reference point. Confirm a signed sample is agreed before production, stored and retained for the supply relationship, and referenced during production and outgoing inspection.

Request: written confirmation of the golden sample process, including storage responsibility and the deviation procedure.

Summary Table

How to Use This SPD Factory Audit Checklist

For a remote documentary audit, request items 1, 2, 5, 7, 8, 9, and 10 before committing to a purchase order. Items 3, 4, and 6 are best verified in person or through a third-party audit service.

Not every supplier passes all ten on a first review — smaller manufacturers often have informal versions of these controls rather than documented procedures. The goal is telling apart process-maturity gaps (correctable over time) from fundamental capability gaps (not correctable without real investment). A supplier who admits gaps and has a plan beats one who claims a perfect score with no paperwork to back it up.

For OEM and custom-branded orders, items 2, 3, 7, and 10 are non-negotiable — these are where undisclosed substitutions and quality shortcuts most commonly happen, and where the liability lands directly on the brand whose name is on the product.