Sunsynk Essential Load Subboard and ATS Wiring Guide

Key Takeaways

• Sunsynk inverters provide backup power to essential loads connected to their dedicated UPS or load output port.
• Neutral-earth bonding is critical for safe islanded operation in South Africa and is managed by inverter settings and external relays.
• Automatic Transfer Switches (ATS) or generator auto-start features allow seamless transition to a generator during grid outages.
• Wiring for essential loads, E-N bonding, and ATS integration must comply with South African standards like NRS 097-2-1.
• Any work involving AC wiring, earthing, or grid-protection settings requires a registered person and a Certificate of Compliance (CoC).

Understanding Sunsynk Essential Load Wiring

Sunsynk hybrid inverters are designed to provide uninterrupted power to critical circuits during grid outages, a common requirement in South Africa due to load-shedding. This is achieved by separating your home's electrical circuits into "essential" and "non-essential" loads. Essential loads are those you need to keep running, such as lights, refrigeration, and Wi-Fi. Non-essential loads, like geysers or pool pumps, can be shed during backup operation.

Your Sunsynk inverter has a dedicated UPS port or load output port specifically for these essential loads. When the grid fails, the inverter automatically switches to battery and PV power to supply only the circuits connected to this port.

To ensure only essential loads are powered, the inverter is typically configured in a mode such as "Zero export + Limit to Load only". In this mode, the inverter will only provide power to any essential loads connected to the inverter's load terminals. This prevents the inverter from attempting to power the entire property or export power to the grid when operating in backup mode.

Neutral-Earth Bonding for Backup Power in South Africa

Neutral-earth (E-N) bonding is a critical safety requirement for electrical installations, particularly when an inverter operates in islanded mode (disconnected from the grid). In South Africa, compliance with NRS 097-2-1 and SANS 10142 is essential. the manufacturer documentation indicates that an E-N bond is required to change the classification of a Sunsynk Inverter from a Class II to a Class I.

Sunsynk inverters manage E-N bonding using specific settings and, in some cases, external relays:

E-N Bond Configuration

Important Note for South Africa: The provided documentation is primarily UK-centric. While the principles of E-N bonding are universal, the specific implementation must adhere to South African wiring codes and standards, such as NRS 097-2-1 and SANS 10142. Always consult with a qualified electrician for compliance.

Integrating an Automatic Transfer Switch (ATS) or Generator Auto-Start

An Automatic Transfer Switch (ATS) or generator auto-start system ensures a seamless transition to a backup generator when grid power is lost. Sunsynk inverters offer features to integrate with compatible generators.

Generator Auto-Start Connections and Requirements

Connecting a Generator with an RCD

If your generator has a built-in Residual Current Device (RCD), specific wiring and settings are required:

• Connection Point: When using a generator that has built in leakage current detection such as an RCD, it is not possible to use the GEN input terminals on the inverter. Instead, the generator MUST be connected to the GRID input terminals.
• Inverter Setting: The "Gen connect to grid" setting MUST be enabled in the inverter settings.
• E-N Bond with RCD Generator: It is not possible to create a permanent earth-neutral bond on the LOAD output side of the inverter if your generator has an RCD. The reason the GRID terminals must be used is because the earth-neutral bond will need to be created when the generator is off and disconnected when the generator is on which is done using 'Signal Island Mode' which operates through the GRID terminals only.
• Three-phase Units: Three-phase units have the built in Earth-Neutral bond switching and all you will need to do is enable 'Signal-Island Mode' in the inverter settings.
• Single-phase Units: On single-phase units, you will need to use the hot/dry contacts on the inverter and a contact relay for E-N bonding.
• Off-grid Systems with RCD Generator: Because there is no grid, an E-N bond needs to be created at the generator itself which should also be earthed using a local earth rod. On the load side, create an E-N bond in the distribution board connected to the load terminals using an NC or NO relay. Common both earth rods to each other so they share a reference to earth.

Generator Charge Conditions

For the inverter to automatically start and charge from the generator, specific battery settings must be enabled:

• The ‘Gen Charge’ and ‘Gen Signal’ must be enabled in the battery settings.
• The battery SOC% must be lower than the ‘GEN Load ON Batt’%.
• Enabling ‘Gen Force’ in the battery settings will override the SOC conditions.

Wiring Considerations for Essential Load Subboards

While the manufacturer documentation does not provide detailed wiring diagrams for essential load subboards, the principle involves physically separating the essential circuits from the non-essential ones.

1. Dedicated Subboard: A common practice is to install a dedicated subboard that receives power exclusively from the Sunsynk inverter's UPS/load output terminals.
2. Circuit Separation: All essential circuits (e.g., specific lights, plugs for critical appliances) are then wired into this new subboard. Non-essential circuits remain connected to the main distribution board, which is supplied by the grid (and potentially the inverter when the grid is active).
3. CT Placement: For accurate load readings, the corresponding CT should always be placed on the live incomer of the property before any henley blocks, distribution boards etc. so that the inverter can read the full load demand as well as import and export before they come in/out of the property. Ensure CT cables are not run closely paralleled to any AC cables or contained in the same trunking to avoid interference.

What you can change yourself, and what you cannot

Understanding the boundary between user-adjustable settings and those requiring a qualified professional is crucial for safety and compliance in South Africa.

What you can change yourself:

You can typically adjust settings related to the inverter's operational mode, such as:

• System Mode: Changing between modes like "Zero export + Limit to Load only" (see /za/guides/fixes/sunsynk-system-mode-and-timer-settings).
• Generator Charge Conditions: Enabling ‘Gen Charge’ and ‘Gen Signal’, and setting the ‘GEN Load ON Batt’% threshold.
• Signal Island Mode: Enabling this in battery settings to activate E-N bonding or ATS port output.

These settings primarily affect how your system uses its stored energy and interacts with your loads, and generally do not impact grid protection.

What you cannot change yourself:

Any work involving AC wiring, earthing, or grid-protection settings must be performed by a registered person (qualified electrician) and requires a Certificate of Compliance (CoC). This includes:

• Physical Wiring: Connecting essential load subboards, ATS units, or generators to the inverter's AC terminals.
• Neutral-Earth Bonding Hardware: Installing contact relays for E-N bonding.
• Grid Settings: Adjusting any parameters that affect the inverter's interaction with the Eskom or municipal grid. the manufacturer documentation explicitly states for UK regulations: "YOU MUST NOT TAKE YOUR INVERTER GRID SETTINGS OUTSIDE OF G98/G99 THIS WILL EFFECT YOUR INVERTER COMPLIANCE WITH UK GRID REGULATIONS." While this refers to UK standards, the principle applies equally to South African NRS 097-2-1 compliance.
• Opening the Inverter Enclosure: This is authorised-service work. If you need to replace a fan, clean heatsink fins, or re-pin a connector, you must isolate PV, battery, and AC breakers, wait the manual's capacitor-discharge time, and ensure the work is done by a qualified technician.

Failure to comply with these requirements can lead to unsafe conditions, damage to equipment, and invalidate your Certificate of Compliance.

What the published sources do not tell you

The Sunsynk documentation provides robust guidance on inverter settings and general wiring principles. However, for a South African context, there are specific gaps:

• South African Standards: The documentation is largely UK-centric, referencing G98/G99 regulations. It does not explicitly detail compliance with South African standards such as NRS 097-2-1 or SANS 10142 for neutral-earth bonding or wiring configurations. Installers must ensure local compliance independently.
• Detailed Essential Load Subboard Wiring Diagrams: While the concept of connecting essential loads to the UPS port is clear, detailed wiring schematics for physically separating an essential load subboard from the main distribution board are not explicitly provided. This requires an installer's expertise to design and implement according to local codes.
• Specific Inverter E-N Bond Capabilities by Model: The documents state that some inverter models have built-in E-N bonds, while others use hot or dry contacts. However, they do not list which specific models fall into each category, requiring installers to consult individual product manuals.
• Manual Transfer Switch Bypass: The articles focus on automatic generator start/stop and relay-based E-N bonding. There is no explicit information regarding the installation or operation of a manual transfer switch bypass for the inverter system itself, which some installations might require for maintenance or fault isolation.