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Can you Combine AC and DC Ground in a Solar Installation?

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Is it Permissible to Interconnect AC and DC Grounding in a Solar Installation?

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Is It Allowed to Use the Same Ground Rod for DC and AC Grounding in a PV System?

The short answer is YES!. The long answer, which includes the pros and cons, depends on your system requirements and applications. Factors affecting the final solution include the nature of grounding, ungrounded AC (floating AC), negative DC floating, whether the equipment chassis is floating, and whether all or any part of the system shares a common ground or none at all.

Outside the U.S., the decision depends on the type of earthing used on the AC side (TT, IT, TN). Despite the TN system typically requiring separate grounding, AC and DC grounding can be combined in TT and IT systems.

Related Post: Why Doesn’t DC System Require a Grounding System Similar to AC System?

Combined Grounding

Grounding and earthing are not designed to indefinitely carry fault current. Instead, protective devices such as ground-fault detection devices (GFDs) and residual current devices (RCDs) are used for automatic isolation during transients and short circuits.

For instance, DC and AC grounding in a solar PV system can be combined. This must follow specific standards (NEC and IEC) and the manufacturer’s instructions. To combine AC and DC grounding, bond the DC system’s common (usually the negative in a non-isolated array) to the inverter’s enclosure. The inverter’s enclosure is then tied to the AC equipment grounding conductor (EGC) at a single defined point. This point is physically connected to the earth using a grounding electrode conductor (GEC) and a ground rod.

The National Electrical Code (NEC) – 690.41 and 690.47(C)(3) allows combining AC and DC grounding and bonding based on system design and requirements. However, it is recommended to use a separate DC grounding electrode for PV arrays and frames. This enhances protection against lightning and transient voltage. For lightning protection associated with grounding systems, refer to NFPA 780 and NEC 250.106.

Similarly, IEC 60364, IEC 62305-3, and BS 7430 suggest connecting the lightning arresters used for PV arrays to the main grounding system. On the other hand, IEC 1100-2005 and IEC 61000-5-2 recommend dedicated and isolated earthing for DC and electronic equipment.

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Separate Grounding

While you are allowed to use the nearest ground rod without installing an additional one to ground the frames of a PV array (especially for lightning protection to safely carry high fault currents back to the earth). However, it is recommended to ground the frames of solar panels directly to the earth using a separate grounding system rather than the building’s grounding system. The reason behind this recommendation is that transients will follow the shortest path to the earth. Hence, high transient voltage will safely dissipate into the ground without affecting the building’s wiring.

Floating DC systems do not require a grounding system because there is no return path for fault currents to the earth. However, in a separate DC grounding system, the ground electrodes should be bonded together to reduce ground resistance.

A separate grounding system for solar panels is beneficial in cases of lightning strikes or faults on transmission lines. The transient current generated during a fault can cause a high transient voltage, which may exceed the operating voltage of DC systems (e.g., 12V, 24V, 48V), potentially damaging the solar cells and other DC components.

An additional advantage of a separate DC grounding system, utilizing a dedicated ground electrode, is the reduction of noise induced by AC-grounded circuits. This separate grounding minimizes the impact of ground loops, which can occur when the inverter’s negative terminal inadvertently forms a secondary ground path.

Related Post: Difference Between Grounding, Earthing and Bonding

AC and DC Grounding in NEC

A grounding system is required for both AC and DC PV systems in accordance with NEC 690.47(C). According to NEC 690.41, one conductor of a 2-wire PV system (either -Ve or +Ve, depending on inverter design) must be grounded if the system voltage exceeds 50 volts.

According to NEC, all metal parts, supporting structures, frames, and equipment in PV systems, or any circuit likely to become energized, must be connected to the grounding system. In modern PV applications, grounded inverters and PV arrays are often not isolated from the grounded output circuits of other inverters.

In such systems, the output neutral connects to the input AC neutral when the system is connected to the AC supply. When the AC disconnects, the back-feed relays open, and a ground relay connects the outgoing neutral to the chassis. This setup ensures the proper operation of ground fault detection devices (GFCI/RCDs).

The NEC provides three grounding methods for solar panels, inverters, DC equipment, and AC mains-connected appliances, depending on system requirements and applications:

Separate DC Grounding Electrode while it is bonded to the AC grounding electrode.
New Grounding Electrode Conductor (GEC) from the Inverter and an Equipment Grounding Conductor (EGC) to the Existing AC Grounding Electrode
Combined DC Grounding Electrode Conductor (GEC) and AC Equipment Grounding Conductor (EGC)

NEC Article 690 (Photovoltaic Systems) and NEC Article 250 (Grounding and Bonding) require that all grounding connections be made at a single point to avoid multiple ground paths, which can lead to ground loops or unwanted circulating currents. Many grid‐tied inverters are designed with their DC common (or negative) internally bonded to the inverter’s chassis, which is then connected to the AC ground via the inverter’s enclosure. This setup is acceptable as long as it meets NEC requirements.

NEC 690.47(C)(3) permits an equipment grounding conductor (EGC) to serve as a bonding conductor between AC and DC systems when using an inverter with ground fault protection. NEC 690.47(D) states that ground-mounted arrays require a local grounding electrode separate from the building grounding electrode system if the array is more than 6 feet (1.8 m) from the premises.

As an exception, NEC emphasizes that installations must follow the listing and labeling provided by the equipment manufacturer’s instructions. Inverters and other components are tested and approved with specific grounding schemes. If the manufacturer specifies that the DC negative can be bonded to the AC grounding system (often via the inverter), then doing so is code-compliant.

The EGC and GEC conductors used for grounding (both DC and AC) must be sized and installed according to NEC 250.104, 250.122 (Table 250.122), 250.134, 250.136, 250.66, and Table 250.66. For example, the DC grounding conductor (sometimes called a bonding conductor) must be continuous and properly sized to handle fault currents.

This means that it is possible to connect the equipment grounding conductor (EGC) of the PV circuit to the grounding point of the inverter. The inverter’s ground point is then connected to the ground electrode in the premises’ main grounding system. This practice eliminates the need for a separate ground rod or a dedicated DC grounding system.

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AC and DC Grounding in IEC

IEC (International Electrotechnical Commission) standards, such as IEC 60364-7-712 for PV installations, require that the system be referenced to earth at a single point. This ensures that all exposed non-current-carrying conductors and metallic parts remain at the same potential. It is acceptable—and often desirable—to tie the DC side (e.g., module frames and the inverter’s DC common) to the same earth reference as the AC side, provided that this connection is made at a designated bonding point.

According to BS 3043 and IEEE 80, combining both earthing systems in close proximity helps reduce potential difference (ΔV). This is important because a voltage difference between both earthing systems can cause serious issues.

IEC 62305-3 and BS 7430 recommend connecting the lightning arrester to the earth electrode and earth pit used for general earthing in a building.

According to IEEE 142-2007, IEC 1100-2005, and IEC 61000-5-2, a dedicated and isolated earthing system is advised for DC and electronic equipment, as required by most manufacturers. However, IEC 61000-5-2 states that an isolated and independent earth electrode for DC-operated electronic systems (such as computers) is not recommended and can be connected to the general earthing system. Additionally, IEEE 1100-2003 discourages the use of isolated grounding for electronic equipment.

According to IEEE 142-2007, IEC-1100-2005 and IEC-6100-5-2, a dedicated and isolated earthing for DC and electronic equipment are advised as required by most of the manufacturers. On the other hand, isolated and independent earth electrode for DC operated electronic systems such as computers is not recommended and can be connected to the general earthing system – IEC-61000-5-2. Additionally, IEEE-1100-2003 discourages the use of isolated ground and isolated grounds for electronic equipment.

According to these standards, a separate earth pit and dedicated terminals should be used for:

Neutral earthing
Lightning protection system earthing
Electronic equipment earthing

However, these earthing points should not be isolated from the main earthing system.

Like the NEC, IEC standards caution against multiple or redundant ground paths. The goal is to prevent unintended current flow, which can lead to electromagnetic interference (EMI) or safety hazards. Therefore, any connection between DC and AC grounding must be carefully engineered.

What This Means for Your Solar System

Allowed? Yes – combining the DC and AC grounds is allowed if it is done at a single bonding point, with proper conductor sizing and routing, and in strict compliance with NEC Article 690/250 and the relevant IEC standards.
How? Typically by bonding the inverter’s DC common (or negative) to its enclosure, which is then tied to the AC equipment grounding system, following the manufacturer’s instructions.
Inverter Design: Many modern inverters are “non-isolated” on the DC side, meaning they are designed to have their DC negative bonded to the AC ground at a specific point. This is a common and accepted practice as long as all components (modules, wiring, disconnects, etc.) are installed according to the applicable codes and standards.
Isolated vs. Non-Isolated Systems:
If you have an inverter with galvanic isolation between the DC and AC sides (or if the system design calls for the DC array to remain “floating”), then you must follow the isolation scheme provided by the manufacturer. In such cases, you would not combine the DC and AC grounds beyond the single point specified (if at all).
Local Codes and Professional Judgment:
Even though NEC and IEC provide general guidelines, local jurisdictions may have additional requirements. It is always a good idea to consult with a qualified electrical professional or inspector familiar with local practices.
Caveats: Ensure that you avoid multiple bonding points to prevent ground loops, and verify that your system (and any isolation requirements) are properly addressed.

Resources:

Can you Combine AC and DC Ground in a Solar Installation?

Is it Permissible to Interconnect AC and DC Grounding in a Solar Installation?