# PG-04 — Protection, Bonding & Grounding Architecture **Project:** Open Solar Trailer **Revision:** A — 17 September 2026 **Status:** Design-review draft. Not a construction drawing, permit determination, or instruction to energize the system. ## Design basis and boundaries This continues [DC-02](https://open-solar-trailer.pages.dev/electrical.html#dc-02) and [AC-03](https://open-solar-trailer.pages.dev/electrical.html#ac-03), without changing the selected architecture: two SmartSolar 150/35 controllers, roof and wing arrays separately wired 2S2P, two 51.2 V batteries in parallel, and one MultiPlus-II 48/5000/70-95 **120 V** inverter/charger. The optional shore inlet and optional 12 V converter remain optional. [P1, P2] The tables distinguish the existing project choices, manufacturer requirements, and proposed implementation. A protection block describes a function; it does not necessarily require a separate purchased enclosure. No new protection hardware has been priced on this sheet. **Construction hold: the DC/PV ground-fault protection and system-reference arrangement is not selected.** The SmartSolar manual states that these controllers have no internal ground-fault protection and describes an external GFPD/GFDI arrangement for US NEC installations. This must be resolved for the actual mobile installation before approving a DC-negative-to-chassis connection. [M2] ## A. Keep three electrical roles distinct | Label | Role in this project | Connection rule | |---|---|---| | **PE1 / AC-PE** | Common protective bonding network | Connects equipment enclosures, outlet grounds and trailer metalwork. Not a normal load-return conductor. | | **AC-N** | 120 V AC neutral | Returns AC load current. Downstream neutral remains isolated from panel metal and PE, except for the approved source bond described in Section C. | | **N1** | System-side DC negative | Returns DC load and charger current through the battery-monitor shunt. Its single proposed connection to PE is a separate, unresolved DC ground-fault design issue. | Do not install a direct AC-N-to-N1 jumper. Their source references can be related through the approved bonding network; that does not make the conductors interchangeable. P0/P1 (positive) and N0/N1 (negative) retain their meanings from DC-02. [P1, P2] ## B. Common equipment-bonding network **Proposed physical arrangement:** a protected PE terminal bar in the equipment compartment, securely bonded to a designated trailer-chassis point, with documented connections to each relevant exposed conductive component. The principle is a continuous, adequately rated, low-impedance fault-return network. [M9] ```mermaid flowchart TB PE["PE1: COMMON EQUIPMENT-BONDING NETWORK
Protective conductors; not normal load returns"] CH["TRAILER CHASSIS / FRAME
Designated durable bonding point"] INV["INVERTER CHASSIS / PE"] MPPT["ROOF AND WING MPPTs
Manufacturer ground terminals"] AC["AC PANEL ENCLOSURE / AC-PE BAR
Receptacle equipment grounds
Not the isolated AC-N bar"] ENC["OTHER CONDUCTIVE EQUIPMENT ENCLOSURES
Battery cases and rack per manufacturer instructions"] RAILS["FIXED ROOF AND SIDE STRUCTURES
Steel backbones / mounting rails"] ROOF["ROOF MODULE FRAMES
Approved module-bonding hardware"] WINGS["FOUR MOVING WING MODULES
Module frames and metal carriers
Dedicated flexible bonds across moving joints"] SHORE["OPTIONAL SHORE PE
Continuous through cord and inlet when connected"] PE --- CH PE --- INV PE --- MPPT PE --- AC PE --- ENC PE --- RAILS RAILS --- ROOF RAILS --- WINGS SHORE -.- PE ``` Solid links show proposed bonding paths, not a mandatory star-shaped cable layout. The dashed shore link denotes equipment absent from the baseline, not a switch in PE. Protective conductors run with the circuits they protect where required; physical routing will be specified on the cable sheet. ### Trailer-specific design details I propose a flexible bonding jumper at **each of the four moving panel assemblies**, with module-to-carrier bonds and fixed-rail-to-chassis bonds documented separately. Do not credit hinges, brace pins, lubricated pivots, painted joints or tow-hitch contact as the sole electrical path. Validate the arrangement through the full folding travel and after transport. Use module-approved lugs or bonding hardware rather than assuming ordinary mounting bolts establish continuity. Do not improvise extra holes in module frames. Specify corrosion-compatible connections, strain relief and protection from sharp edges, UV and pinching. These are implementation requirements to verify against the final panel and mounting manuals, not an assertion that a particular lug or jumper has already been approved. Maintain local chassis bonding when the tow vehicle and shore cord are disconnected. Follow the inverter's mobile-installation instructions. [M1] Battery-case grounding terminals, case-to-negative isolation and any internal bonds must be checked before connection; those battery details remain unverified. **No routine switch or fuse is placed in an equipment protective-earth conductor.** The specialized DC system-reference/GFDI function below is not an equipment-ground switch. [P2] ## C. AC neutral-to-ground behavior The proposed AC configuration retains the MultiPlus's intended internal ground-relay function. Its configuration manual describes bonding output neutral to the chassis when the AC-input relays are open. [M7] | Mode | Source-reference behavior to verify | Downstream requirement | |---|---|---| | Inverter supplies loads; no accepted external AC | Internal relay supplies the inverter's neutral-to-PE source bond. | AC-N bar remains insulated from the enclosure and AC-PE. | | Approved shore AC accepted | Internal ground relay opens before AC transfer; the accepted supply must have the appropriate source grounding arrangement. | No extra neutral-ground bond in the trailer panel or adapters. | | External supply disappears | Verify the transfer sequence restores the inverter's intended source reference. | Local protective bonding remains intact. | The transfer behavior is described in the installation manual. [M1] These are commissioning requirements, not instructions to manually wire around the relay. Do not bridge AC input and output neutrals around the inverter. A future generator, particularly one with a floating neutral, needs a separate source/bonding review; no bonding-plug solution is assumed. [P2] ### AC ground-fault and overcurrent protection Keep AC-03's **Q-OUT/GF-OUT** functions downstream of AC-out-1. Victron specifies UL 943-compliant output residual-current protection plus overcurrent protection. [M1] Retain the proposed 30 A output main, 30 A RV branch and two 20 A branches only as project planning selections. [P2] Select a compatible personnel-GFCI assembly rather than substituting an unspecified leakage device. The load hot and neutral follow its specified sensing paths; PE does not become a neutral bypass. Final whole-output versus coordinated branch implementation requires review. An input-side GFCI alone is not the proposed output protection when inverting. Do not remove GFCI protection or the intended bond to stop a trip. The shared-output arrangement may stop mobility charging when another load faults; selective protection is an open design question, not an existing capability. [P2] ## D. DC system reference and ground-fault protection — unresolved This is **not** a drawing of an approved hard jumper from DC negative to chassis. ```mermaid flowchart LR N0["N0: BATTERY NEGATIVES ONLY"] SH["SH1: BATTERY-MONITOR SHUNT"] N1["N1: SYSTEM NEGATIVE
All charger and load returns"] GFD["GF-DC: PROPOSED SINGLE DC REFERENCE
WITH COORDINATED GROUND-FAULT PROTECTION
HOLD: device, trip coverage and topology unresolved"] PE["PE1 / CHASSIS BONDING NETWORK"] N0 --- SH SH --- N1 N1 -.- GFD GFD -.- PE ``` The **N1 location is a project design proposal**, derived from preserving the shunt boundary: the SmartShunt manual places all load/charger returns on its system side and excludes other connections from its battery side. [M3] Final GFPD instructions and manufacturer review must confirm this topology. The SmartSolar instructions call for a single system grounding point through a GFDI in the described US arrangement, and no separate grounding of PV positive or PV negative. [M2] Therefore: - Do not add one battery-negative/chassis jumper per battery or controller. - Do not install a parallel hard bond that bypasses the selected ground-fault sensing path. - Do not create a shunt bypass through N0, a battery case, a communications cable or a non-isolated accessory. - Do not treat an AC GFCI or a battery fuse as the missing DC/PV ground-fault function. **GF-DC is a functional placeholder, not a component already present.** The installer must select the method, covered circuits, trip devices and reset behavior for both MPPTs and the shared battery bus. The exact installation classification and governing requirements also need determination. This sheet does not approve a homemade ground-fuse circuit, an unmonitored floating DC system, or an exemption. A ground-fault trip may alter the circuit's reference to chassis; treat the system as faulted and potentially hazardous until diagnosed. [M2] ## E. Protection and isolation schedule This schedule elaborates the functions already reserved in DC-02 and AC-03. It does not duplicate devices automatically. [P1, P2] | ID / location | Required function in the proposed design | Selection status | |---|---|---| | **F-B1 / F-B2**, individual battery positives | Source fault protection and a safe service-isolation arrangement for each battery | Class T remains the BOM approach; ratings, holders, source isolation and backfeed coordination unresolved. | | **Q-BANK**, common bank feeder | Protect/isolate combined feeder as required by its routing and all connected sources | Must coordinate with individual battery protection; not an all-source shutdown. | | **F-INV / S-INV**, P1 to inverter | Protect inverter feeder and isolate it from the battery bus | Coordinate with Q-BANK; do not add redundant hardware without an identified purpose. | | **F-MR / S-MR**, P1 to roof MPPT BAT+ | Protect and isolate battery-side controller branch | Separate function from roof PV isolator. | | **F-MW / S-MW**, P1 to wing MPPT BAT+ | Protect and isolate battery-side controller branch | Separate function from wing PV isolators. | | **S-R / S-L / S-W**, PV inputs | Simultaneous isolation of each circuit's PV conductors | PV-rated load-break devices; coordinate poles with final grounded-conductor scheme. No independently opened negative-only switch. | | **PV string/combiner protection** | Protect conductors/modules against applicable reverse feed and faults | Assess final module maximum series-fuse rating, parallel-string contributions, current corrections and equipment instructions. Two parallel strings do not by themselves settle the fuse decision. | | **GF-DC** | DC/PV ground-fault detection and coordinated interruption | **Not selected or priced.** | | **Q-OUT / GF-OUT** | AC output overcurrent/disconnect and personnel-GFCI protection | Existing AC-03 proposal; exact assembly and neutral path unresolved. | | **Q-RV / Q-MOB / Q-CAMP** | AC branch protection | Existing 30/20/20 A proposals; share the one source limit. | | **Q-IN**, optional shore input | Protect/isolate accepted external AC input | Source, cord, inlet and transfer coordination required. | | **Optional DC-DC branch** | Protected converter input and separately protected 12 V outputs | No direct 12 V load connection to the 51.2 V bank; converter/reference choice unresolved. | | **Monitor and sense leads** | Protect small conductors from their source | Include the manufacturer-fused SmartShunt supply at P0; it can remain powered with Q-BANK open. | ### Manufacturer rating references — not a cable release | Equipment | Published reference | Application limit | |---|---|---| | MultiPlus-II **48/5000/70** | **200 A DC fuse** in the manufacturer's sizing table | Inverter-feeder starting point, **not 200 A for each 100 Ah battery**. Cable, source capability, fault current and upstream coordination still control. [M1] | | Each SmartSolar **150/35** | **40–45 A battery fuse range** | Battery-side protection, not PV-string fuse sizing. [M2] | Confirm an explicit DC voltage rating, adequate interrupting rating at that voltage, and suitability for current in every possible direction. A fuse/breaker's amperage alone is insufficient. Do not presume a 12/24 V automotive part works on this bank, or that an upstream fuse automatically makes a low-interrupting-capacity downstream breaker acceptable. [M5] Battery BMS protection is not credited as a substitute for the external cable/protection functions in this design. Before release, confirm battery temperature and charge/discharge limits, all simultaneous charging sources, and operation after one parallel battery disconnects. [P1] ## F. Chassis bonding versus an earth electrode The equipment-bonding network must function locally; the design does not use soil as its intentional return conductor. It is intended to give a fault a metallic path back to the relevant source/protection system. [D1; M9] **Whether a deployed earth electrode is required remains an installation/event review item.** The mobile grounding discussion in Wiring Unlimited describes interconnected metalwork as the local reference, but that is not an exemption decision for a trailer supplying equipment around a temporary event. [M4] If an electrode is required, integrate it into the approved common grounding design. A separate rod is not a replacement for PE conductors, and a mechanical wing anchor is not automatically an electrical electrode. No lightning-protection rating is claimed. ## G. Shutdown and service boundaries An accessible **AC OFF** control is a proposed operational feature, not proof that PV, batteries or the inverter's DC input are de-energized. No automatic all-source emergency-stop system has been designed. [P1, P2] The completed installation needs an approved, labeled service procedure covering external AC, inverter operation, both PV arrays, controller battery supplies, battery branches, optional DC loads, small sense supplies and stored charge. For the SmartSolar controllers, the published sequence is **PV disconnected before battery supply; battery restored before PV**. [M6] Folding a panel is not electrical isolation. Source-side solar wiring can remain energized in daylight, and a battery remains a source upstream of its disconnect. Never use unmating PV connectors as a load-break operation. [D1; M8] Service work must prevent reconnection and account for retained energy; verify absence of voltage at the actual work location using appropriate procedures. An app's off setting, a blank screen or an open output breaker is not an all-source lockout. The cited safety-order material supports lockout and stored-energy precautions; applicability to this exact project is not determined here. [M10] ## H. Proposed commissioning record **Qualified-person work; not a request to create live short circuits or touch energized terminals.** Use appropriate test instruments and manufacturer procedures. | Check | Evidence to retain | |---|---| | Equipment identities and polarity | Exact models; both PV inputs and battery paths checked before energizing. | | PE continuity | Document paths to chassis, receptacle grounds, equipment cases, roof frames, side rails and every wing in both positions. | | AC source modes | Verify intended bond/transfer behavior and personnel-protection operation in every enabled mode. A GFCI test button alone is not proof of the complete grounding network. | | DC reference and GF-DC | Document only the approved reference path, ground-fault detection/trip coverage and no bypassing second bond. | | Shunt and case isolation | Confirm no battery-negative case/accessory route bypasses SH1 or GF-DC. | | Protection coordination | Record device DC ratings, interrupting capacity, time-current coordination, conductor sizing and terminal torque requirements. | | Thermal/load and battery controls | Verify ventilation, charger settings, low/high-temperature behavior and one-battery-unavailable response without intentionally overloading hardware. | | Isolation and restart | Validate the final tagged procedure and identify all still-live source-side terminals. | ## I. Budget and drawing updates before procurement Obtain a quote for **the approved DC/PV ground-fault arrangement, AC output GFCI/protection assembly, four wing bonding jumpers, approved module-bonding hardware, equipment-ground conductors and terminals, and any missing service disconnects**. Reconcile these against existing BOM allowances rather than adding everything twice. Do not change inverter/MPPT quantities or budget a third MPPT as a substitute for protection. No total-cost change is asserted until the selected hardware is priced. **Release gates:** approved grounding/GF-DC design; exact protective devices and fault-current/ampacity coordination; final battery/control integration; optional-shore decision; installer/event acceptance requirements; and a completed commissioning record. --- ## Source notes **Project-derived** [P1] Supplied **Open_Solar_Trailer_DC_Architecture.md**, DC-02: P0/P1/N0/N1 definitions, shunt boundary, protective functions, unresolved battery integration and all-source shutdown. [P2] Supplied **Open_Solar_Trailer_AC_Architecture.md**, AC-03 Revision A: one 120 V source, AC-out-1, proposed main/branches, UL 943 output-protection function, optional shore input and no downstream neutral bond. **External manufacturer/safety checks — accessed 17 September 2026** [M1] Victron MultiPlus-II 120V, Installation, sections 4.1, 4.3 and 4.4: DC disconnection/fuse reference, mobile chassis bonding and output protection. https://www.victronenergy.com/media/pg/MultiPlus-II_120V/en/installation.html [M2] Victron SmartSolar 150/35–150/45, Installation, sections 4.2–4.4: battery-fuse range, PV isolation, single grounding point and external ground-fault protection. https://www.victronenergy.com/media/pg/Manual_SmartSolar_MPPT_150-35__150-45/en/installation.html [M3] Victron SmartShunt, Installation, section 3.4: battery/system sides and fused supply lead. https://www.victronenergy.com/media/pg/SmartShunt/en/installation.html [M4] Victron Wiring Unlimited, Ground, earth and electrical safety, especially mobile installations and system grounding. General background, not a jurisdiction-specific installation approval. https://www.victronenergy.com/media/pg/The_Wiring_Unlimited_book/en/ground,-earth-and-electrical-safety.html [M5] Victron Wiring Unlimited, DC wiring, sections 4.6–4.7: fusing, interrupting capacity and isolation-switch selection. https://www.victronenergy.com/media/pg/The_Wiring_Unlimited_book/en/dc-wiring.html [M6] Victron SmartSolar 150/35–150/45, Operation, section 6.5: shutdown and restart order. https://www.victronenergy.com/media/pg/Manual_SmartSolar_MPPT_150-35__150-45/en/operation.html [M7] Victron MultiPlus-II 120V, Configuration: ground-relay behavior and battery-specific settings. https://www.victronenergy.com/media/pg/MultiPlus-II_120V/en/configuration.html [M8] Victron SmartSolar 150/35–150/45, Safety precautions: PV illumination, terminals, operating environment and strain relief. https://www.victronenergy.com/media/pg/Manual_SmartSolar_MPPT_150-35__150-45/en/safety-precautions.html [M9] California DIR, Title 8 section 2395.51, Effective Grounding. Used for the fault-path principle, not an applicability finding. https://www.dir.ca.gov/title8/2395_51.html [M10] California DIR, Title 8 section 2320.4, De-Energized Equipment or Systems. Used for lockout/stored-energy principles, not an applicability finding. https://www.dir.ca.gov/title8/2320_4.html [D1] Project-specific design reasoning and proposed review/commissioning actions. The source manuals support the component requirements, not approval of this complete custom installation.