Guide slug: /guides/cn-sea-dc-string-reverse-r14/ · TradVolt maintenance/process series · Audience: B2B green-tech trade · Language: EN · Reviewer: muse-ba · Evidence-date: 2026-09-22.
Verdict / answer: Run the 11-step, 14-day DC string reverse sequence below on any CN→sea-deployed PV asset where a string, sub-string, or polarity segment is wired in reverse topology, reverse polarity, or reversed module orientation relative to the as-built drawing or OEM datasheet. Equipment scope (fixed for this revision): LONGi Hi-MO 6 LR5-66HTH module family, SolarEdge S-Series S440/S500 power optimiser, Sungrow SG125HT string inverter, and a generic PV combiner (model per site). Horizon: Day 0–Day 14, with re-energisation no earlier than Day 8. Do not close the DC switch until Voc, Isc and IR are within the OEM bands below and zero DC is verified at the inverter DC switch per LOTO. Limitation: this guide covers string-level maintenance only; it is not a commissioning handbook and not a root-cause design review.
| Decision | Value |
|---|---|
| Trigger condition | Reverse polarity / reversed string topology / reversed module orientation on a CN→sea PV asset |
| Equipment family | LONGi Hi-MO 6 LR5-66HTH + SolarEdge S440/S500 + Sungrow SG125HT + site-specific combiner |
| Location | CN→sea corridor (coastal export route, salt-air zone) |
| Horizon | 14 days (Day 0 mobilisation → Day 14 evidence-pack close-out) |
| Voc tolerance | ±5% of LONGi STC Voc (LR5-66HTH datasheet rev 2024-03, LONGi Hi-MO X6 page) |
| Isc tolerance | Within SolarEdge S-Series optimiser max input Isc (S440/S500 datasheet rev 2024-01) |
| Insulation resistance (min) | ≥ 1 MΩ per IEC 62446-1:2016 / UL 61730-1 PV module safety qualification |
| Connector torque | Stäubli MC4: 2.5 N·m (housing) per OEM installation manual (manual rev confirmed at RFQ) |
| Thermography irradiance | ≥ 600 W/m², project threshold aligned with IEC 62446-1:2016 commissioning/inspection guidance |
| LOTO zero-DC verification | 0 V DC measured at inverter DC switch and string combiner, two-person sign-off |
| Re-energise gate | Earliest Day 8, after remediation log signed and I-V curve within OEM tolerance band |
| Evidence pack | cn-sea-evidence-pack-r14.zip indexed, hashed, customs entry reference recorded |
This guide covers the maintenance/process sequence for a recurring field event on solar PV assets traded or operated across the China-to-sea (CN→sea) segment: DC string reverse. For this revision, DC string reverse is defined (project convention) as: any DC string, sub-string, or polarity segment wired in reverse topology, reverse polarity, or with reversed module orientation relative to the as-built drawing or OEM datasheet, including optimiser-driven polarity reversals detected at the inverter. The guide is written for EPC O&M teams, asset managers, and trade-side logistics coordinators who receive or service equipment routed through coastal sea corridors where salt-air, UV, and container-handling stresses are routine.
The equipment family bound to this revision is: LONGi Hi-MO 6 LR5-66HTH module family (see LONGi Hi-MO X6 product page; Hi-MO 6 LR5-66HTH datasheet rev 2024-03, retrieved 2026-09-22), SolarEdge S-Series S440 / S500 power optimiser (SolarEdge S-Series datasheet rev 2024-01, retrieved 2026-09-22; URL published by SolarEdge in its S-Series product family materials — full datasheet PDF published by SolarEdge in the S-Series family pack, retrieved 2026-09-22), Sungrow SG125HT string inverter (see Sungrow string-inverter range page, SG125HT datasheet rev 2023-11, retrieved 2026-09-22), and a site-specific PV combiner selected per project. This is an internal maintenance process guide, not a commissioning handbook. It assumes the reader already holds the OEM datasheet pack for these four device families and is conducting a planned string-level intervention rather than a root-cause design review. For root-cause classification, consult the OEM installation manuals cited in the claim-row footer.
One owner per row. Inputs and outputs are the literal filenames a field or trade team would hand off. Done-when states the verifiable exit condition. Torque values, Voc tolerance, and IR minimum are taken from the OEM datasheets cited above (LONGi LR5-66HTH rev 2024-03; SolarEdge S-Series rev 2024-01; Sungrow SG125HT rev 2023-11; Stäubli MC4 installation manual).
| Step# | Action | Owner | Input doc | Output doc | Done-when |
|---|---|---|---|---|---|
| 1 | Scope the asset and CN→sea corridor segment | Asset manager | asset-register-master.csv | scope-note-r14-v01.docx | Site ID, string count, last service date and corridor segment recorded in scope note; equipment family confirmed as LONGi Hi-MO 6 LR5-66HTH + SolarEdge S440/S500 + Sungrow SG125HT + site combiner. |
| 2 | Retrieve OEM datasheets for module, optimiser, inverter, combiner | O&M engineer | oem-datasheet-pack.zip | datasheet-index-r14.xlsx | LONGi LR5-66HTH rev 2024-03 (LONGi Hi-MO X6 page), SolarEdge S-Series S440/S500 rev 2024-01 (SolarEdge S-Series datasheet pack), Sungrow SG125HT rev 2023-11 (Sungrow string-inverter range), and combiner OEM datasheet present; revision dated within 24 months. |
| 3 | Lock-out tag-out (LOTO) and verify zero DC at inverter DC switch | Authorised technician | loto-procedure-r14.pdf | loto-record-r14.pdf | Verified 0 V DC at the Sungrow SG125HT DC switch and at the string combiner output, signed by issuer and witness (two-person sign-off). |
| 4 | Visual inspection of connectors, cabling, routing, salt-air effects | Field technician | inspection-form-r14.pdf | inspection-report-r14.pdf | Photo set captured, defects coded (Stäubli MC4 connector condition logged), serial-control blanks signed. |
| 5 | Measure Voc, Isc and insulation resistance per string | Commissioning engineer | iv-test-procedure-r14.pdf | string-test-results-r14.csv | Voc within ±5% of LONGi LR5-66HTH STC Voc (datasheet rev 2024-03, LONGi Hi-MO X6 page); Isc within SolarEdge S440/S500 max-input Isc (datasheet rev 2024-01, SolarEdge S-Series datasheet pack); IR ≥ 1 MΩ per IEC 62446-1:2016 and UL 61730-1 PV module safety qualification. |
| 6 | Identify reverse-polarity or reversed-string topology | O&M engineer | string-test-results-r14.csv, as-built-dwg-r14.pdf | reverse-findings-r14.docx | Each suspect string flagged by ID, with polarity sign and topology deviation noted against LONGi LR5-66HTH (LONGi Hi-MO X6 page) and SolarEdge S-Series polarity marking (S-Series datasheet pack). |
| 7 | Remediate connectors and re-terminate to OEM torque | Field technician | reverse-findings-r14.docx, Stäubli MC4 installation manual | remediation-log-r14.pdf | Damaged connectors replaced; Stäubli MC4 housing re-torqued to 2.5 N·m per OEM installation manual (manual rev confirmed at RFQ), torque values recorded per connector ID. |
| 8 | Restore topology, re-energise, ramp string-by-string | Commissioning engineer | remediation-log-r14.pdf, Sungrow SG125HT datasheet | re-energise-record-r14.pdf | Sungrow SG125HT DC switch closed, string-by-string ramp observed within inverter input window, no fault flags, signed handover. |
| 9 | Run thermal imaging and I-V curve trace | Commissioning engineer | re-energise-record-r14.pdf | thermogram-set-r14.zip, iv-curve-r14.csv | Thermograms captured under ≥ 600 W/m² irradiance, project threshold aligned with IEC 62446-1:2016 commissioning/inspection guidance; I-V curves within LONGi LR5-66HTH datasheet tolerance band (LONGi Hi-MO X6 page). |
| 10 | Update corridor logbook and asset register | Asset manager | thermogram-set-r14.zip, iv-curve-r14.csv | logbook-entry-r14.pdf, asset-register-master.csv (updated) | Logbook entry countersigned, asset register row updated with service date and OEM revisions cited. |
| 11 | Attach evidence to customs/cert pack if re-export or warranty swap applies | Trade compliance | logbook-entry-r14.pdf | cn-sea-evidence-pack-r14.zip | Evidence pack indexed, hash logged, customs entry reference recorded against the destination customs lookup tool (EU TARIC, USITC HTS, UK Global Tariff, Japan Customs, ABF, SARS, GRA, or URA as applicable). |
Tick each item before signing off the corridor record. Filenames are literal; do not rename inside the pack.
scope-note-r14-v01.docxdatasheet-index-r14.xlsxloto-procedure-r14.pdfloto-record-r14.pdfinspection-form-r14.pdfinspection-report-r14.pdfiv-test-procedure-r14.pdfstring-test-results-r14.csvas-built-dwg-r14.pdfreverse-findings-r14.docxremediation-log-r14.pdfre-energise-record-r14.pdfthermogram-set-r14.zipiv-curve-r14.csvlogbook-entry-r14.pdfcn-sea-evidence-pack-r14.zipNo direct PDF download is exposed on this page; checklist and supporting evidence-pack templates are issued on RFQ submission to keep revisions under TradVolt editorial control.
| Phase | Window | Owner | Milestone |
|---|---|---|---|
| Pre-mobilisation | Day 0–Day 2 | Asset manager | Scope note issued, LONGi / SolarEdge / Sungrow datasheet pack confirmed |
| Site isolation | Day 2–3 | Authorised technician | LOTO recorded, 0 V DC verified at Sungrow SG125HT DC switch |
| Inspection & testing | Day 3–5 | Field technician / commissioning engineer | Inspection report, string test results filed (Voc, Isc, IR) |
| Remediation | Day 5–8 | Field technician | Re-terminations complete, Stäubli MC4 torque log signed at 2.5 N·m |
| Re-energise & verification | Day 8–10 | Commissioning engineer | Ramp confirmed, thermograms and I-V curves filed at ≥ 600 W/m² |
| Records & trade evidence | Day 10–14 | Asset manager / trade compliance | Logbook updated, customs/cert evidence pack indexed against the destination tariff lookup tool |
All cost slots below are indicative placeholders, not prices. TradVolt does not publish hard figures here. Replace with quoted values per project before procurement. Cost rates are classified as model assumptions pending RFQ confirmation.
| Cost slot | Basis | Value (indicative) | Status |
|---|---|---|---|
| Labour — O&M engineer, day rate | Per-day, per engineer | UNCERTAIN | Model assumption — confirm at RFQ |
| Labour — authorised technician, day rate | Per-day, per technician | UNCERTAIN | Model assumption — confirm at RFQ |
| Labour — commissioning engineer, day rate | Per-day, per engineer | UNCERTAIN | Model assumption — confirm at RFQ |
| Mobilisation — CN→sea corridor segment | Per-segment travel & lodging | UNCERTAIN | Model assumption — confirm at RFQ |
| Consumables — replacement Stäubli MC4 connectors | Per-unit | UNCERTAIN | Model assumption — confirm at RFQ |
| Consumables — PV-rated cable, UV/salt-air grade | Per-metre | UNCERTAIN | Model assumption — confirm at RFQ |
| Test equipment — megohmmeter hire/rental | Per-day | UNCERTAIN | Model assumption — confirm at RFQ |
| Test equipment — thermal camera hire/rental | Per-day | UNCERTAIN | Model assumption — confirm at RFQ |
| Documentation & cert handling fee | Per evidence pack | UNCERTAIN | Model assumption — confirm at RFQ |
| Contingency allowance | % of subtotal | UNCERTAIN | Model assumption — confirm at RFQ |
| HS reference | Description (illustrative) | Rate | Status / lookup tool |
|---|---|---|---|
| 8541.43 | Photovoltaic cells, assembled in modules or made up into panels (LONGi Hi-MO 6 LR5-66HTH) | PENDING | Verify at USITC HTS · EU TARIC · UK Global Tariff · Japan Customs · ABF · SARS · GRA · URA |
| 8504.40 | Static converters — Sungrow SG125HT inverter | PENDING | Verify at the destination tariff lookup tool above |
| 8504.40 | Static converters — SolarEdge S440/S500 power optimiser (optimiser classification per destination authority) | PENDING | Verify at the destination tariff lookup tool above |
| 8536.69 | Plugs, sockets and connectors for photovoltaic use (Stäubli MC4) | PENDING | Verify at the destination tariff lookup tool above |
| 8544.49 | Other electric conductors, PV-rated | PENDING | Verify at the destination tariff lookup tool above |
Disclaimer: Rates above are marked PENDING and must be verified against the destination customs authority at the time of shipment using the linked WCO HS nomenclature framework and the national tariff lookup tool for the corridor leg (EU TARIC, USITC HTS, UK Global Tariff, Japan Customs, ABF, SARS, GRA, or URA as applicable). TradVolt does not warrant the accuracy of duty rates and is not liable for misclassification. Final classification is the importer of record's responsibility.
cn-sea-evidence-pack-r14.zip) is filled in and countersigned. Trade compliance retains the final say on whether the pack is admissible against the destination tariff lookup tool.oem-datasheet-pack.zip.| Claim | Source | File / section |
|---|---|---|
| Guide covers a maintenance/process sequence for DC string reverse events on solar PV assets. | Project convention (TradVolt editorial layout). | §Scope; lead decision table |
| One owner per step in the step-sequence table. | Project convention (TradVolt editorial layout). | §Step-sequence table |
| Voc tolerance band of ±5% relative to LONGi LR5-66HTH STC value. | LONGi Hi-MO X6 product page — Hi-MO 6 LR5-66HTH datasheet rev 2024-03 (Voc STC and tolerance; ±5% treated as project-convention comparator band). | string-test-results-r14.csv header notes; §Step-sequence row 5 |
| Isc tolerance per SolarEdge S440/S500 max-input Isc. | SolarEdge S-Series S440/S500 datasheet rev 2024-01, S-Series datasheet pack (full datasheet PDF published by SolarEdge in the S-Series family pack, retrieved 2026-09-22). | string-test-results-r14.csv; §Step-sequence row 5 |
| Insulation resistance minimum ≥ 1 MΩ per string. | UL 61730-1 PV Module Safety Qualification — Part 1 (insulation-resistance test method) and IEC 62446-1:2016 — PV systems, requirements for testing, documentation and maintenance — Part 1: Grid connected systems (TC 82). | iv-test-procedure-r14.pdf §3; §Step-sequence row 5 |
| Thermal imaging minimum irradiance threshold (≥ 600 W/m²) for PV thermography. | IEC 62446-1:2016 PV system commissioning/inspection guidance. Threshold is project convention. | thermogram-set-r14.zip EXIF metadata; §Step-sequence row 9 |
| Stäubli MC4 connector housing torque 2.5 N·m. | Stäubli MC4 installation manual (OEM manual; rev confirmed at RFQ). | remediation-log-r14.pdf torque column; §Step-sequence row 7 |
| LOTO zero-DC verification at inverter DC switch and string combiner, two-person sign-off. | Project convention (TradVolt editorial layout). | §Step-sequence row 3; loto-record-r14.pdf |
| HS code 8541.43 is the illustrative reference for PV modules. | USITC Harmonized Tariff Schedule (search 8541.43) and EU TARIC — WCO HS nomenclature 8541.43 (photovoltaic cells assembled in modules or panels). | §HS code & duty block |
| HS code 8504.40 covers static converters (Sungrow SG125HT inverter; SolarEdge S440/S500 optimiser classification per destination authority). | USITC HTS and EU TARIC — WCO HS nomenclature 8504.40 (static converters). | §HS code & duty block |
| HS code 8536.69 covers plugs and sockets (Stäubli MC4). | UK Global Tariff and USITC HTS — WCO HS nomenclature 8536.69 (plugs and sockets). | §HS code & duty block |
| HS code 8544.49 covers other electric conductors (PV-rated cable). | USITC HTS and UK Global Tariff — WCO HS nomenclature 8544.49 (other electric conductors). | §HS code & duty block |
| Duty rates are pending and require lookup at point of entry against the destination tariff lookup tool. | EU TARIC · USITC HTS · UK Global Tariff · Japan Customs · ABF · SARS · GRA · URA. | §HS code & duty block disclaimer |
| Cost slots are indicative placeholders, not prices; classified as model assumptions pending RFQ. | Project convention (TradVolt editorial layout). | §Indicative cost slots |
| Lithium-battery handling and sea-corridor transport provisions are adjacent to (not covered by) this guide. | UN Manual of Tests and Criteria (UN 38.3, ST/SG/AC.10/11/Rev.7) — cited only as adjacent reference where batteries are part of the corridor pack; IATA DGR for adjacent air-leg note. Not part of the DC string reverse scope. | §Scope (adjacent reference only) |