BESS Installation Electrical Scope of Work: How Responsibility Is Split Between the Battery Supplier, the EPC Contractor and the Electrical Contractor

A BESS (battery energy storage system) installation typically consists of six work packages: engineering and design, civil works, main equipment supply, site electrical works, communications infrastructure, and testing and commissioning. The main equipment includes the battery containers, the power conversion system (PCS), the step-up transformer and the medium-voltage (MV) switchgear. Site electrical works cover the cabling, grounding and auxiliary power that connect this equipment to each other and to the grid.

Each package falls within a different party's area of expertise, and problems usually surface at the interfaces where the packages meet. Take the grounding tails cast into a container foundation: they look like civil work, but if they are left in the wrong position, they directly affect the electrical contractor's work. That is why the most important document at the bid stage of an energy storage project is a responsibility matrix that defines every work package and every interface, one by one.

Site electrical works themselves progress in three waves. Before the equipment arrives, the grounding grid, conduits and cable trench infrastructure are completed; once the containers and PCS units are set in place, cable pulling and terminations follow; the final wave is preparation for testing and commissioning. Because cable crews cannot work in the same area on the days when containers are being lifted into position, the crane schedule and the electrical works schedule should be prepared together.

In the most common model, connections inside the containers and the PCS sit with the battery supplier, site connections between equipment sit with the electrical contractor, and overall system integrity and coordination remain with the EPC contractor. This split varies from contract to contract; in skid-type solutions, where the PCS, transformer and MV switchgear arrive factory-assembled on a single skid, the number of site connections drops and the boundaries shift. The breakdown below summarizes a model frequently encountered on site and can serve as a starting point for bid discussions.

Battery supplier: the battery container (racks, modules, BMS, HVAC, fire detection and suppression), DC cabling inside the container, factory testing and commissioning supervision. Depending on the contract, the PCS and the EMS software may belong to the supplier or to a separate system integrator. Civil works, meaning foundations, cable trenches, ducts and site roads, are usually handled by the EPC contractor's civil subcontractor.

Electrical contractor: DC cabling between the containers and the PCS, the LV connection between the PCS and the transformer, and the MV cabling and cable terminations running from the transformer to the MV switchgear and from the switchgear to the switchyard. The site grounding grid, equipotential bonding, auxiliary power panels, and fiber optic installation and splicing also fall within this scope. The EPC contractor is responsible for design approval, the grid connection process, defining the protection settings and managing all interfaces.

The matrix must answer "who supplies it" as clearly as "who installs it." If it does not state which party provides cable lugs, MV termination kits, cable glands and fiber patch panels, crews waiting on materials and variation claims become inevitable on site.

Cabling on a BESS site is planned by treating the DC and AC sides on separate routes and under separate rules. On the DC side, voltage in current systems commonly reaches up to 1500 V DC; the cable insulation class is selected for this voltage level, the cross-section for current-carrying capacity and voltage drop, and the short-circuit rating for the expected fault current of the battery system. Labeling positive and negative conductors, recording tightening torques at every connection point and protecting cable ends from moisture are the core disciplines of DC cabling.

On the AC side, the low-voltage output of the PCS is stepped up to MV through the step-up transformer and carried by MV cables to the switchgear or the switchyard. Here, cable sizing is based not only on current-carrying capacity but also on the installation method, cable grouping, soil thermal resistivity and short-circuit conditions. The screen bonding method and the termination type for the MV cables should also be defined at the design stage.

A frequently overlooked item is auxiliary power: container HVAC, fire detection and suppression systems, lighting and control equipment all require a separate LV distribution network. This supply usually comes from an auxiliary service transformer or a separate grid connection, and critical loads are backed up by UPS against outages. The responsibility matrix should state separately which party owns the auxiliary power panels and cables.

Route planning keeps power cables separated from communications cables, runs road crossings through protective conduit and leaves access for future maintenance. If cable quantities are calculated before the container layout is finalized, reels that turn out too short or too long on site cost both time and money.

Grounding of BESS containers is critical because it is the system that prevents dangerous touch voltages on metal enclosures during a fault and ensures that protective devices operate correctly. The battery containers, PCS, transformer and MV switchgear must all be connected to the same site grounding grid, with no potential difference left between pieces of equipment. This equipotential arrangement is necessary both for personnel safety and for protecting sensitive control and communications equipment.

In practice, grounding work starts before the foundations are poured: the buried grounding conductor and the container connection tails must be left in the correct position in coordination with the civil team. Connections are made by exothermic welding or with suitable connectors, and points that will later become inaccessible are documented with photos and records. The relationship between the lightning protection system and the site grounding grid should also be clearly defined in the design.

Once the installation is complete, grounding resistance and continuity measurements are taken, and the results are evaluated against Türkiye's Regulation on Grounding in Electrical Installations (Elektrik Tesislerinde Topraklamalar Yönetmeliği) and the project specification. Having the team that built the grounding also report the measurement results removes any later ambiguity over responsibility.

In most projects, the physical installation of fiber optic and communications cables is part of the electrical works, while the software and configuration side of communications usually stays with the supplier or the system integrator. The BMS monitors the battery cells and reports operating limits to the PCS; the EMS manages the charge and discharge strategy and passes data to SCADA. On site, the physical backbone of this chain consists of fiber optic cables, splice enclosures, patch panels and copper communications cables.

The electrical contractor's scope typically covers pulling fiber cable through conduit or ducts, making fusion splices, terminating at patch panels and reporting with OTDR measurements. Communication protocol settings, the IP plan, EMS software parameterization and SCADA integration should be written up as a separate line item. If the contract does not draw this line, a responsibility gap opens at exactly the point where "the cable is pulled, but the system isn't communicating."

Before the system is energized, the electrical contractor completes pre-commissioning tests and hands over the records demonstrating that every connection it installed is correct and safe. These tests are a prerequisite for the supplier to move on to functional commissioning. Which tests will be witnessed by the owner's or the EPC contractor's representative should be defined in an inspection and test plan (ITP) before work begins.

A typical test package includes insulation resistance and continuity measurements on DC and LV cables, polarity checks on the DC side, and torque checks and marking at connection points. Added to these are VLF withstand testing and outer sheath testing on MV cables, phase sequence checks, OTDR measurements on fiber links, and grounding resistance and continuity measurements. Every test is performed with instruments in current calibration, and readings are recorded together with the date and instrument details.

Beyond the test results, the handover file includes as-built drawings, the cable schedule, termination and splice records, and the punch list. Secondary injection testing of the protection relays and the energization program are usually planned together with the EPC contractor or a specialist testing team.

When requesting a quote for BESS electrical works, at least five topics should be clarified in writing: scope boundaries, material supply split, quantity basis, test list and site conditions. For scope boundaries, ask exactly which terminal or busbar each connection starts from and where it ends; for the supply split, ask who provides the cable, termination kits, lugs, fiber and grounding materials.

For the quantity basis, establish whether excavation and backfill are included, who owns the cable tray and conduit work, and how quantity variations will be priced. For site conditions, discuss crane and heavy equipment support, work permits at an operating plant, lockout/tagout (LOTO) procedures and how standby time will be treated. A reliable price emerges only once these items and the site survey are settled.

Miratek Elektrik undertakes cable pulling, MV cable terminations, fiber optics, grounding and testing on BESS, solar power plant (SPP) and wind farm sites across Türkiye. The BESS electrical works we are carrying out for Chint Power Systems at the Killik Wind Farm site in Tokat are a concrete example of how the responsibility split described here works in the field; we have shared the details in our project article. Reviewing the scope matrix together before bidding is the step that saves the most time on site.