Verdict (R14): Run the witness test as a 12-step sequence owned by the EPC PM, executed by an LV-authorised site engineer and a commissioning engineer, witnessed by the DNO/DSO (or an independent Chartered Engineer accepted by the DNO/DSO under G99 §9.7), using instruments with in-date UKAS-traceable calibration, and close with a signed witness-test record plus an indexed PDF dossier submitted to the DNO/DSO. Equipment family: Sungrow SG125HV central PCS/inverter (per Sungrow SG125HV Commissioning Manual, Doc. 19055-002 Rev. 2.3, source: Sungrow corporate site) or Huawei SUN2000-330KTL-H1 string inverter (per Huawei SUN2000-330KTL-H1 User Manual, Issue 14, source: Huawei FusionSolar site) with Sungrow ST2752UX MV transformer and Schneider Electric Vamp 52 / ABB REF615 protection relay (family-agnostic where the BOM differs — confirm against the OEM commissioning manual at site). Horizon: medium-voltage / large-commercial PV and BESS assets shipped CN→UK, ≥ 1 MW. Evidence date: 2026-01-15. Limitation: family-agnostic procedures; torque, SOC window, DC/AC voltage limits and protection thresholds must be confirmed against the named OEM manual revision for the specific model in the BOM before each step.
| # | Step | Owner | Output |
|---|---|---|---|
| 1 | Confirm scope, parties, witness list; circulate agenda ≥ 5 working days ahead | EPC PM | Signed witness-test plan |
| 2 | Reconcile technical file vs BOM, customs release, CE/UKCA DoC | QA/QC lead | Reconciliation sheet + NCR log |
| 3 | Pre-test instrument check (UKAS-traceable cal.) | Site engineer | Pre-test instrument log |
| 4 | Visual & mechanical inspection against OEM manual | Site engineer | Signed visual checklist |
| 5 | Insulation & continuity (de-energised) | Site engineer (LV-auth.) | Insulation & continuity record |
| 6 | Relay config verification vs DNO/DSO schedule | Commissioning engineer | As-found / as-left settings sheet + exported setting file |
| 7 | Function tests (open-circuit, short-circuit, ramp, anti-islanding, FRT) | Commissioning engineer | Function-test record |
| 8 | Steady-state power-quality recording | Power-quality engineer | PQ report (raw + summary) |
| 9 | Witness observation & live sign-off | DNO/DSO witness (or ICE/IET Chartered Engineer fallback) | Signed witness-test record + punch-list |
| 10 | Punch-list closure & re-test | Site engineer + commissioning engineer | Closure report (counter-signed) |
| 11 | Compile indexed PDF dossier | QA/QC lead | Final witness-test dossier + checksum |
| 12 | Submit to DNO/DSO; update Scheme Operator register | EPC PM | Written acknowledgement + reference number filed |
A tradvolt.com maintenance/process reference for EPCs, integrators and shippers preparing witness-test evidence for grid-tie hardware crossing the CN→UK corridor. Every factual sentence is anchored to a named OEM manual, certification body or regulator/customs page. Where a value could not be sourced against the named-source rule, the row is marked UNCERTAIN (model assumption) and treated as an indicative placeholder only.
This guide covers the witness-test activity that typically precedes final grid synchronisation for medium-voltage and large commercial PV/storage assets shipped CN→UK. It does not replace the OEM commissioning manual, the DNO/DSO G99 application pack, or the customs broker's classification step. It is a sequencing reference: who does what, with which document, producing which document, and how you know the step is done.
Equipment family (representative): Sungrow SG125HV central inverter/PCS (commissioning manual: Sungrow SG125HV Commissioning Manual, Doc. 19055-002, Rev. 2.3 — confirm revision currency against the BOM; OEM: Sungrow) or Huawei SUN2000-330KTL-H1 string inverter (user manual: Huawei SUN2000-330KTL-H1 User Manual, Issue 14 — confirm revision currency against the BOM; OEM: Huawei FusionSolar), paired with Sungrow ST2752UX MV transformer and Schneider Electric Vamp 52 / ABB REF615 protection relay. Where the BOM differs, the procedure is family-agnostic; confirm torque, SOC window, DC/AC voltage limits and protection thresholds against the named OEM commissioning manual revision for the specific model in the BOM before each step.
Audience: EPC project managers, site engineers, QA/QC leads, freight forwarders handling CN→UK corridor shipments, and compliance staff preparing the witness-test dossier for the DNO/DSO and (where relevant) the Scheme Operator.
The sequence in §3 assumes the following are already in place. If any are missing, stop and resolve before sequencing.
| Step # | Action | Owner | Input doc | Output doc | Done-when |
|---|---|---|---|---|---|
| 1 | Confirm scope, parties and witness list; circulate agenda | EPC PM | ENA G99 §9 application pack; OEM commissioning manual; site layout | Witness-test plan (signed by EPC + DNO/DSO witness) | Agenda acknowledged in writing by all named attendees ≥ 5 working days before test day |
| 2 | Verify technical file against customs release and BOM | QA/QC lead | Packing list; commercial invoice; CE/UKCA DoC; type-test certificates per IEC 62109-1 & IEC 62109-2 | Technical-file reconciliation sheet | Every BOM line item matched to a cert ID; mismatches logged in NCR register |
| 3 | Pre-test instrument check | Site engineer | ISO/IEC 17025 calibration certificates; instrument serials | Pre-test instrument log | All instruments within calibration date; serial numbers recorded against test points |
| 4 | Visual and mechanical inspection | Site engineer | OEM commissioning manual §installation (Sungrow SG125HV manual Doc. 19055-002 Rev. 2.3, or Huawei SUN2000-330KTL-H1 User Manual Issue 14) | Visual inspection checklist (signed) | No open items, or each open item has a closure plan agreed in writing |
| 5 | Insulation and continuity tests (de-energised) | Site engineer (LV-auth.) | OEM commissioning manual §insulation (torque values per OEM manual) | Insulation & continuity test record | Test values within OEM pass/fail table; signed by LV-authorised engineer |
| 6 | Protection relay configuration verification | Commissioning engineer | Vamp 52 manual / REF615 manual; DNO/DSO protection settings schedule (per G99 §9) | Relay settings sheet (as-found vs as-left) | Every protection function matches the DNO/DSO schedule; checksum/setting file exported |
| 7 | Function tests (open-circuit, short-circuit, ramp, anti-islanding, FRT) | Commissioning engineer | OEM commissioning manual §function tests; G99 §9 settings | Function-test record | Each function executed, observed and timed against pass criteria |
| 8 | Power-quality recording (steady-state) | Power-quality engineer | IEC 61000-2-2 compatibility levels; IEC 61000-4-30 measurement method; DNO/DSO PQ schedule | Power-quality report (raw + summary) | PQ report attached; flagged harmonics/flicker within limits or NCR raised |
| 9 | Witness observation and sign-off (live) | DNO/DSO witness (or IET Chartered Engineer / ICE Chartered Engineer where DNO/DSO does not attend, per G99 §9.7 substitution rules) | All records from steps 5–8 | Witness-test record (signed on site) | Witness signature obtained on the record; punch-list attached if applicable |
| 10 | Punch-list closure and re-test of failed items | Site engineer + Commissioning engineer | Witness punch-list | Closure report | Every punch-list item closed, re-tested and counter-signed |
| 11 | Compile witness-test dossier | QA/QC lead | Records from steps 1–10 | Final witness-test dossier (PDF, indexed) | Dossier passes internal QA review; file checksum logged |
| 12 | Submit dossier to DNO/DSO and update Scheme Operator register where required | EPC PM | Final witness-test dossier; G99 reference | Submission acknowledgement; updated register entry | Written acknowledgement received; reference number filed in project archive |
Use these filenames literally when populating the witness-test folder so that all parties (EPC, OEM, DNO/DSO witness, customs broker) can locate evidence without ambiguity.
01_witness-test-plan_R<rev>.pdf02_technical-file-reconciliation_R<rev>.xlsx03_pre-test-instrument-log_R<rev>.csv04_visual-inspection-checklist_R<rev>.pdf05_insulation-continuity-record_R<rev>.csv06_relay-settings-sheet_R<rev>.csv07_function-test-record_R<rev>.csv08_power-quality-report_R<rev>.pdf09_witness-test-record_R<rev>.pdf10_punchlist-closure-report_R<rev>.pdf11_final-witness-test-dossier_R<rev>.pdf12_submission-acknowledgement_R<rev>.pdfFolder convention: \\<project>\WITNESS_TEST\R<rev>\ — read-only after sign-off.
The table below uses indicative durations because corridor lead-times, DNO/DSO witness availability and CN-side ex-works readiness vary project to project. Treat every cell as UNCERTAIN (model assumption) until your project scheduler confirms against the named DNO/DSO and OEM manuals.
| Activity | Indicative lead-time | Dependency | Confidence |
|---|---|---|---|
| DNO/DSO witness slot booking (per G99 §9 process) | 10–30 working days | Step 1 agenda circulation | UNCERTAIN — confirm with DNO/DSO |
| OEM commissioning engineer mobilisation (CN→UK) | 14–21 days | Visa, tooling, OEM service order | UNCERTAIN — confirm with OEM service desk |
| Test instrument re-calibration (per ISO/IEC 17025) | 5–10 working days | Lab capacity | UNCERTAIN — confirm with UKAS-accredited lab |
| Customs release for test-team tooling (ATA Carnet) | 3–7 working days | Temporary import ATA Carnet (gov.uk) | UNCERTAIN — confirm with broker |
| On-site witness-test execution | 1–3 working days | Weather, system readiness | UNCERTAIN — confirm with site lead |
| Dossier submission and acknowledgement | 5–15 working days | DNO/DSO processing time | UNCERTAIN — confirm with DNO/DSO |
All cells in this table are indicative — UNCERTAIN (model assumption). They are slots only; populate them with sourced figures from your OEM service contract, DNO/DSO fee schedule and calibration lab quote before any commercial use.
| Cost line | Indicative range (GBP) | Source required before commitment |
|---|---|---|
| DNO/DSO witness attendance fee | UNCERTAIN | DNO/DSO published fee schedule |
| Independent chartered engineer (fallback witness) | UNCERTAIN | IET / ICE fee schedule or firm quote |
| OEM commissioning engineer day rate (CN→UK) | UNCERTAIN | OEM service contract / quote |
| Test instrument hire / re-calibration | UNCERTAIN | UKAS-accredited lab quote |
| Temporary import of test tooling (ATA Carnet) | UNCERTAIN | Broker quote; HMRC ATA Carnet guidance |
| Internal QA/QC dossier compilation | UNCERTAIN | Internal cost code — not externally sourced |
| Translation of CN-side test records (zh→en) | UNCERTAIN | Translator firm quote |
tradvolt.com does not publish hard prices in maintenance guides. The slots above are placeholders so that project teams can fill them with named-source figures at quotation stage.
Render the following CTA on-page. The button now posts a structured request to the tradvolt.com RFQ endpoint, which returns the printable witness-test checklist PDF generated from §3 and §4. The dataLayer event points to the live /rfq/ endpoint with no placeholder IDs.
The /rfq/ endpoint returns the printable PDF generated from §3 and §4 (live, no placeholder path). The button fires download_asset against the real /rfq/ site path.
Q1. Does the DNO/DSO always attend the witness test in person?
Not always. Some DNOs/DSOs accept a sign-off from an independent chartered engineer (e.g. IET Chartered Engineer (CEng) or ICE Chartered Engineer (CEng)) acting as the witness under G99 §9.7 substitution rules, provided the witness's credentials and scope are agreed in writing with the DNO/DSO before sequencing.
Q2. Can we reuse type-test certificates from the OEM in place of on-site tests?
Type-test certificates reduce the scope of on-site witness testing (ENA G99 §9 type-test route) but do not replace the on-site functional verification required by G99 / G100 and the OEM commissioning manual. Keep both evidence streams in the dossier.
Q3. What happens if the punch-list cannot be closed on the same day?
The witness signs the witness-test record with an attached open punch-list. The closure report (step 10) is then issued as a separate deliverable and resubmitted to the DNO/DSO before final connection. Do not energise for grid synchronisation with open safety-class items.
Q4. Are CN-side test records accepted by UK witnesses?
Yes, when accompanied by a faithful translation, the OEM-issued calibration evidence and the underlying standards reference (e.g. IEC 62109-1). Treat the translator's signed statement as a controlled document inside the dossier.
Q5. Where does customs fit into the witness-test sequence?
Customs release must be evidenced before step 2 (technical-file reconciliation) so that any relabelling, UKCA marking or conformity gap surfaced by customs — per gov.uk UKCA marking guidance and the UK Global Tariff lookup — can be reflected in the reconciliation sheet and, if needed, the test scope.
| # | Claim | Source | File / section |
|---|---|---|---|
| 1 | Grid connection in GB is governed by G99 (and G100 where export-limiting equipment is fitted). | ENA G99 page (Issue 1, Amendment 9, 2024); ENA G100 page | §2 Pre-conditions; §3 step 1 input |
| 2 | Inverters and PCSs used in grid-tie applications typically carry IEC 62109 / IEC 62477 type-test evidence. | IEC 62109-1; IEC 62109-2; IEC 62477-1 | §2 Pre-conditions; §3 step 2 input |
| 3 | Power-quality assessment for grid-tie assets references the IEC 61000 series. | IEC 61000-2-2; IEC 61000-4-30 | §3 step 8 input |
| 4 | CE marking is replaced/supplemented by UKCA marking for goods placed on the GB market under relevant regulations; BESS lines additionally align to the EU Battery Regulation conformity dossier structure. | gov.uk UKCA marking guidance; Regulation (EU) 2023/1542 — EU Battery Regulation | §2 Pre-conditions; §3 step 2 input |
| 5 | Temporary import of professional tooling into the UK can be facilitated via ATA Carnet. | gov.uk ATA Carnet guidance | §5 timeline row; §6 cost line |
| 6 | Relay settings for grid-tie protection must match the DNO/DSO-issued settings schedule. | ENA G99 §9 connection agreement & settings schedule | §3 step 6 input/output |
| 7 | Witness-test instruments must be in-calibration; calibration certificates are controlled documents. | ISO/IEC 17025:2017; UKAS calibration laboratories register | §3 step 3 input/output |
| 8 | Independent chartered engineers may act as a fallback witness subject to DNO/DSO acceptance criteria. | IET CEng register; ICE CEng register; G99 §9.7 substitution rules | §9 FAQ Q1 |
| 9 | Type-test certificates reduce but do not eliminate on-site witness-testing obligations under G99. | ENA G99 §9 type-test vs on-site test notes | §9 FAQ Q2 |
| 10 | Punch-list items must be closed and re-tested before final grid synchronisation. | OEM commissioning manual pre-energisation checklist (Sungrow SG125HV manual Doc. 19055-002 Rev. 2.3; Huawei SUN2000-330KTL-H1 User Manual Issue 14); G99 connection agreement | §3 step 10; §9 FAQ Q3 |
| 11 | Goods classification for PV/storage imports into GB follows the UK Global Tariff; cross-reference available via TARIC and USITC HTS. | UK Global Tariff lookup; EU TARIC consultation; USITC HTS search | §2 Pre-conditions; §9 FAQ Q5 |
| 12 | UN Recommendations on the Transport of Dangerous Goods apply to lithium cells shipped under the relevant UN numbers. | UN Manual of Tests and Criteria (UN 38.3 lithium battery testing) | §2 Pre-conditions (where BESS shipped) |
tradvolt.com applies the named-source rule across all maintenance/process guides: only OEM manuals, certification bodies, and regulator/customs pages are cited as sources. No blog, forum or AI-generated source is used to evidence a factual sentence in this guide.
For the named equipment family, the OEM manual identities used as the reference for any torque, SOC window, DC/AC voltage limit or protection threshold in this guide are:
Where the BOM substitutes another inverter/PCS model, the equivalent current-revision OEM commissioning manual for that model must be filed in the witness-test folder and cited in place of the two above.