The grid‑connected photovoltaic cabinet serves as the “interface” between a solar power plant and the grid, performing multiple functions such as power collection, protection, isolation, and metering. Many newcomers to the PV field often wonder: Is its wiring really that complicated?

The answer is: The principle is straightforward, but the standards are extremely stringent. — Wiring errors not only affect power generation but may also lead to safety accidents. This article will examine… Main circuit (primary) wiring, secondary circuit wiring, grounding system Three dimensions to thoroughly explain the wiring process.

1. First, clarify: Where is the grid‑connected photovoltaic cabinet connected?

Before officially starting the wiring, it is essential to first understand the grid‑connection cabinet’s role within the overall system:

Photovoltaic module → Inverter → Grid‑connection cabinet → Grid/load

Inbound side : Connect the AC output terminals of the inverter

Outbound side : Connect to the low-voltage side of the grid‑connected transformer or to the incoming switchgear in the distribution room.

Location Selection : It is recommended that the distance between the grid‑connected cabinet and the inverter be ≤5 meters to minimize line voltage drop, and the distance to the grid connection point must comply with the requirements of the local power authority.

Now that the location has been confirmed, let’s move on to the main topic: the wiring stage.

II. Preparations Before Wiring: The Three Bottom Lines Must Be Upheld

1. Environmental Condition Verification

The installation location of the grid‑connection cabinet must… Ventilated, dry, and free of corrosive gases

When installed outdoors, the protection rating must meet IP54 and above

The installation base must be level and stable, with a maintenance access passage provided (width ≥ 1 meter).

2. Grounding System Preparation

Ground resistance ≤ 4 Ω (In areas with high soil resistivity, the limit may be relaxed to 10 Ω.)

This is the foundation of the entire system’s security and must be verified in advance.

3. Equipment and Parameter Verification

Confirm the grid‑connected cabinet’s rated voltage (380 V) and rated current (based on the inverter’s maximum output current). 1.2 to 1.5 times Selection)

Inspect internal components: verify that the circuit breaker, surge protective device (SPD), busbars, and terminal blocks are all present and in good condition.

III. Main Circuit (Primary Circuit) Wiring: The Core of the Power Transmission System

The primary circuit wiring involves establishing the power path from the inverter, through the grid‑connection cabinet, to the utility grid; this constitutes the core task of grid‑connection cabinet wiring.

1. Basic Wiring Sequence

Step 1: Connect the inverter’s output cable to the incoming terminal of the grid‑connection cabinet.

Connect the cable from the inverter’s AC output terminal to the grid‑connection cabinet. Incoming circuit breaker (or isolating switch) For a three-phase system, the L1, L2, and L3 phase conductors, as well as the N neutral conductor, must be connected.

Step 2: Connect the outgoing terminals of the grid‑connection cabinet to the power grid.

A cable is routed from the outgoing circuit breaker of the grid‑connection cabinet and connected to… Low-voltage side of the power grid transformer Alternatively, the incoming switchgear in the distribution room. The cable cross-sectional area must be determined based on the current-carrying capacity—for example, a 50 kW inverter has an output current of approximately 90 A; it is recommended to use a 50 mm² copper cable.

Step 3: Busbar Connection Inside the Cabinet

When multiple inverters are paralleled, the outgoing terminals of the incoming circuit breakers must be connected to the main busbar inside the cabinet, from which the power is then uniformly routed to the grid side.

2. Key Wiring Details

The phase sequence must be strictly distinguished. ：

Incorrect phase sequence connection can prevent equipment from operating properly and may even cause damage.

Cable Crimping Specifications ：

After the cable enters the cabinet, it must be fitted with copper lugs of the appropriate specifications.

Use Specialized crimping pliers Single-time compression

All bolts must be used with Torque wrench Tighten to the specified torque as required by the equipment—loosening under high current can easily lead to overheating.

Circuit Breaker Wiring Orientation: A Key Detail Often Overlooked

In photovoltaic grid‑connected switchgear, since the inverter is on the supply side, it is common for… “Bottom in, top out” The wiring method.

Here is a common misconception: Not all circuit breakers support reverse wiring. . Ordinary miniature circuit breakers are generally not permitted to have the incoming conductor connected in reverse; otherwise, arc extinction becomes difficult when interrupting fault currents, which may result in the breaker being damaged or even causing a short circuit.

Solution : If a bottom-entry wiring method must be used, a model explicitly labeled as supporting reverse entry should be selected. Photovoltaic-specific circuit breaker or a specific model of molded-case circuit breaker.

IV. Secondary Circuit Wiring: Metering, Protection, and Control

The secondary circuit is responsible for signal acquisition, protection and control, and electrical energy metering, serving as the “nervous system” of the grid‑connection cabinet.

1. Electrical Energy Metering Wiring

Grid‑connected cabinets are typically built‑in. Two-way energy meter , used to measure both the electricity fed into and drawn from the grid.

Key Wiring Points ：

Voltage circuit: Obtain the voltage signal (L1/L2/L3/N) from the upstream side of the circuit breaker.

Current circuit: The wiring of current transformers (CTs) is strictly directional. — P1 faces the busbar side; S1/S2 are connected to the corresponding terminals of the meter. Reversing the connections may cause the meter to run backward or result in inaccurate measurements.

Secondary circuit cross-section: The cross-sectional area of control circuit conductors shall not be less than 1.5mm² (Multi-strand copper stranded wire), with terminal blocks having a rated voltage of not less than 1000 V and a rated current of not less than 10 A.

2. Wiring of Protective Devices

The dedicated circuit breakers built into grid‑connection cabinets typically provide the following protection functions:

Wiring logic : Overcurrent relays and undervoltage relays shall be connected to their respective monitoring circuits, with signal outputs routed to the monitoring system (RS485/Ethernet).

3. Anti-Islanding Protection and Communication

The anti-islanding protection device shall be connected to the incoming side of the grid‑connection cabinet and, upon detecting a grid outage, shall automatically disconnect the inverter output. The communication line (RS485) must be properly interfaced with the monitoring system to enable remote data acquisition and control.

4. Secondary Wiring Standards

Neatly arranged, use Numbered casing Marking wire number

Terminal block reservation 20% spare terminals

Adopt Flame-retardant terminal , both ends of the wire are marked with numbers.

V. Grounding System: The Lifeline of Safety

Grounding of the grid‑connection cabinet is fundamental to ensuring safety and must be carried out in strict accordance with relevant standards.

1. Arrangement of the grounding busbar

The cabinet is equipped with a dedicated… Grounding copper busbar (PE busbar) , All of the following equipment must be consolidated here:

Inverter grounding wire

Grounding of the cabinet body and doors

Surge Protective Device (SPD) Grounding Conductor

The PE conductor of the incoming cable

2. Final Ground Connection

The grounding busbar shall be connected via a conductor of adequate cross-sectional area to… Independent grounding electrode Reliable connection; the grounding resistance shall meet the design requirements (typically ≤4 Ω).

3. Key Wiring Points for Surge Protective Devices (SPDs)

The SPD is connected in parallel at the incoming line terminal of the grid‑connection cabinet.

The grounding conductor shall be routed separately to the grounding busbar. , length ≤ 0.5 meters

An excessively long SPD grounding conductor can severely compromise protective performance.

VI. Commissioning and Acceptance After Wiring Is Completed

Wiring is only the first step; verifying correctness is what truly matters.

Only after all tests have been confirmed to be satisfactory may the system be commissioned and connected to the grid.

VII. Overview of Common Wiring Errors

Key Considerations for Wiring Photovoltaic Grid-Connected Cabinets

Returning to the original question— How exactly should a grid‑connected photovoltaic cabinet be wired? To summarize, the following core principles apply:

Primary circuit : Inverter → incoming circuit breaker → busbar → outgoing circuit breaker → grid; the three phases must strictly follow the phase sequence, and the circuit breakers must be selected to support reverse incoming connections.

Secondary circuit : The CT polarity must not be reversed, the energy meter wiring must be correct, and the protection settings must be configured in accordance with grid requirements.

Grounding system All grounding conductors are routed to the PE busbar and ultimately connected to an independent grounding electrode, with a grounding resistance not exceeding 4 Ω.

Acceptance testing : Phase sequence inspection, insulation testing, grounding testing, and meter verification—none of these can be omitted.

The wiring of a grid‑connected photovoltaic cabinet is not merely a matter of cable connections; it is an electrical engineering task directly linked to system safety and power generation revenue. Rigorous, standardized installation is the cornerstone for ensuring the long‑term, stable operation of a photovoltaic system.

Hunan Electrical Appliance Co., Ltd. As a professional manufacturer of complete electrical equipment covering the entire value chain, we possess in-house R&D, production, and service capabilities for photovoltaic grid‑connected switchgear (boxes). Our product range includes residential‑grade grid‑connected boxes and commercial/industrial grid‑connected switchgear, which can be configured with dedicated circuit breakers, metering devices, and anti‑islanding protection in accordance with grid‑operator requirements. For technical consultation or assistance with product selection, please feel free to contact us.