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Analysis by Marcus & Team

Generic Smart Circuit Backup Load Shedding Failure

Troubleshoot a Backup Load Shedding Failure on a Generic Smart Circuit Hybrid Inverter. Identify causes and solutions for residential power systems.

Frequently Asked Questions

•What is the typical lifespan of load shedding relays in a hybrid inverter?

The lifespan of load shedding relays depends on their duty cycle and operating conditions. Generally, they are rated for several thousand to tens of thousands of cycles. Regular inspection and testing can help identify relays that are nearing the end of their service life.

•How can I determine the correct load shedding settings for my Smart Circuit inverter?

The correct load shedding settings depend on the size of the battery bank and the power consumption of the protected loads. Consult the inverter's manual or contact the manufacturer for guidance on determining the appropriate settings.

•What are the NEC requirements for rapid shutdown in residential solar systems?

NEC Article 690.12 specifies the requirements for rapid shutdown of PV systems. It mandates that a means be provided to reduce the voltage of PV circuits to 30 volts or less within 30 seconds of initiating the shutdown. This is typically achieved using rapid shutdown devices (RSDs) located at the module level or string level.

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Marcus leads the technical research department at Storage Faults. Together with a team of systems analysts, he specializes in translating complex solar storage error codes into actionable diagnostic steps for the US market.

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What to Look For:

During a grid outage, critical loads connected to the Smart Circuit are not powered, despite the battery bank having sufficient state of charge (SOC) and the inverter being in backup mode. The system may report a “Load Shedding Failure” or similar error in the monitoring app. Voltage measurements at the protected load terminals are zero or significantly below the expected AC voltage (e.g., less than 100VAC when 120VAC is expected).

Why This Happens:

Defective load shedding relay or contactor within the Smart Circuit inverter.
Firmware bug or software error in the inverter's control system.
Incorrect configuration of load shedding parameters in the inverter's settings.
Low battery state of charge (SOC) preventing the inverter from switching to backup mode, even if load shedding is not active.
Communication failure between the inverter and the load shedding module (if a separate module is used).
Overload condition on the protected loads exceeding the inverter's backup capacity, causing it to shut down the output.

Technical Background:

Hybrid inverters manage power flow between solar panels, battery storage, the grid, and protected loads. The backup load shedding function is designed to disconnect non-critical loads during an outage to preserve battery capacity for essential circuits. This is typically achieved using internal relays or contactors controlled by the inverter's control system. Failure can occur in the control logic, relay hardware, or communication pathways responsible for shedding loads. Proper operation depends on accurate voltage/current sensing and adherence to programmed load shedding profiles. AC coupling from the grid and rapid shutdown compliance per NEC 2017/2020 also influences functionality.

Safety Warning:

Hybrid inverters operate with high DC voltages (up to 600V or more). Always disconnect the DC disconnect switch and AC breaker before performing any maintenance or troubleshooting. Arc flash hazards exist when working with energized equipment. Only qualified electricians should perform invasive measurements or repairs. Follow all NEC guidelines for rapid shutdown and personal protective equipment (PPE). Never work on live circuits without proper training and safety precautions.

Recommended Action:

1

Verify the battery SOC using the inverter's monitoring app or display. If the SOC is below the minimum threshold for backup operation (typically 20-30%), charge the battery using solar or grid power.
2

Inspect the load shedding relay or contactor (if accessible) for signs of physical damage or overheating. Use a multimeter to check for continuity across the relay contacts in both the open and closed positions. Disconnect AC power before inspection.
3

Review the load shedding configuration settings in the inverter's programming interface. Ensure that the correct loads are designated as non-critical and that the load shedding thresholds (e.g., voltage, current, SOC) are properly configured.
4

Check for any error codes or alarms in the inverter's monitoring system. Consult the inverter's manual for troubleshooting guidance specific to the reported error.
5

Measure the AC voltage and current at the protected load terminals during a simulated outage (by disconnecting grid power). Use a clamp meter to verify that the current draw of the connected loads does not exceed the inverter's backup capacity.
6

If the inverter has a separate load shedding module, verify the communication link between the inverter and the module. Check the wiring connections and ensure that the module is powered on.
7

Update the inverter's firmware to the latest version. Firmware updates often include bug fixes and performance improvements that can resolve load shedding issues.

Pro Tip:

Access the inverter's service menu (refer to the manufacturer's service manual for the key combination) to view real-time relay status and load shedding parameters. This can provide valuable insights into the cause of the failure and help to isolate the problem to a specific component or setting. Also, some inverters have a “test load shed” function that allows you to manually activate the load shedding relays for testing purposes.

Maintenance Tips:

Regularly monitor the battery SOC and state of health (SOH) using the inverter's monitoring system
Perform periodic capacity tests to ensure that the battery can provide the expected backup power
Check the tightness of electrical connections and inspect for signs of corrosion
Keep the inverter's firmware up-to-date
Perform thermal scans of the inverter enclosure using an IR thermometer to identify hotspots which may indicate failing components