NRS 097-2-1:2024 is the standard that every grid-tied solar system in South Africa must comply with. It governs how inverters interact with the low-voltage distribution network — specifically the protection settings that ensure a solar system disconnects safely when the grid fails. If an inverter stays connected during a grid fault, it can endanger the safety of utility workers trying to restore power. That is why NRS 097 compliance is non-negotiable for Eskom and every municipality.
This guide covers the standard’s key requirements, the inverter protection settings it mandates, and what changed in the 2024 update.
Factory Default Settings Are Not NRS 097-Compliant
Inverters configured for European or global markets typically have a default frequency operating range of 47–53 Hz. NRS 097 requires a trip at 51.5 Hz. If you commission a South African system with factory defaults, the inverter will not comply — and Eskom or the municipality will reject or revoke the SSEG approval when they check commissioning documentation.
What NRS 097-2-1 Covers
NRS 097-2-1 addresses the interface between a solar PV system and the distribution network. Its scope covers:
| Topic | NRS 097-2-1 Requirement |
|---|---|
| Inverter type approval | Type-test certificate from accredited lab mandatory |
| Frequency protection | Over/under frequency trip thresholds and clearing times |
| Voltage protection | Over/under voltage trip thresholds |
| Anti-islanding | Active and passive detection both required |
| Power factor | 0.9 lag to 0.9 lead at rated output |
| Reconnection | Mandatory delay after grid restoration (typically 60 seconds) |
| Export limiting | Provisions for active power limitation where required by network |
| Metering | Bidirectional metering requirements for net metering SSEG |
| Hybrid systems | Additional requirements for battery storage in grid-tied systems (2024 update) |
Protection Settings in Detail
Frequency Protection
The South African grid operates at 50 Hz. NRS 097-2-1:2024 requires inverters to disconnect when the grid frequency deviates significantly from 50 Hz:
| Condition | Trip Threshold | Clearing Time |
|---|---|---|
| Over-frequency | 51.5 Hz | 10 cycles (200 ms at 50 Hz) |
| Under-frequency | 47.5 Hz | 10 cycles (200 ms at 50 Hz) |
Why 51.5 Hz matters: Eskom’s grid has historically experienced frequency excursions above 51 Hz during load shedding block transitions. The 51.5 Hz trip threshold ensures solar inverters disconnect before the grid frequency reaches an unsafe level. The European default of 52 Hz would leave inverters connected well into a frequency excursion — hence the NRS 097 requirement is stricter.
Voltage Protection
| Condition | Trip Threshold | Notes |
|---|---|---|
| Over-voltage | 110% of nominal (253 V for 230 V nominal) | |
| Under-voltage | 80% of nominal (184 V for 230 V nominal) |
Nominal voltage in South Africa is 230 V (single-phase) or 400 V (three-phase line-to-line). The over-voltage threshold is relatively tight at 110% — some network areas with high SSEG penetration experience voltage rise during peak generation periods, and the 110% trip protects the network.
Anti-Islanding Protection
Anti-islanding is the inverter’s ability to detect when it is operating in isolation (the grid has disconnected) and shut down immediately. NRS 097-2-1 requires both:
- Passive methods: Detecting frequency or voltage deviations that indicate grid loss
- Active methods: Injecting a small perturbation to detect impedance changes that indicate islanding
Passive detection alone is insufficient under NRS 097 because in a perfectly balanced island condition (load exactly equals generation), passive detection can fail to detect islanding. Active detection provides the backup.
Reconnection After Grid Restoration
After the grid is restored following a disconnection, the inverter must wait before reconnecting. NRS 097-2-1 specifies a minimum reconnection delay (typically 60 seconds) after frequency and voltage return to normal limits. This prevents multiple inverters from reconnecting simultaneously and creating a transient overload.
The 2024 Update: Key Changes
The 2024 revision of NRS 097-2-1 is the most significant update since the 2017 edition. The key changes for installers:
1. Hybrid system provisions: The 2024 edition includes a dedicated annexure for battery-hybrid systems, covering the interaction between the battery inverter and grid protection. Hybrid systems must maintain anti-islanding protection even when operating in battery backup mode.
2. Reactive power requirements: The power factor requirement was clarified and the reactive power capability requirement for larger systems (above 5 kVA) was tightened.
3. Type-testing methodology: The anti-islanding test methodology was updated to require more rigorous testing procedures, particularly for active anti-islanding methods.
4. Active power limitation: New provisions for active power limitation (export curtailment) were added to address network operator requirements in constrained areas.
Inverter Acceptance: Practical Steps
The inverter acceptance process with Eskom and municipalities is a common point of delay. Here is how to avoid it:
Check the network operator’s accepted list first
Before specifying an inverter, check Eskom’s website or contact the relevant municipality to verify the model is accepted. Eskom publishes an accepted inverter list at eskom.co.za. This takes 5 minutes and can prevent a 30-day delay.
Request the NRS 097 type-test certificate from the distributor
If the model is not on the accepted list, request the NRS 097-2-1 type-test certificate from the manufacturer or local distributor. Confirm it was tested against NRS 097-2-1 (not just IEC 62109). Submit the certificate with the SSEG application and note that it is being submitted for Eskom technical review.
Verify settings in the commissioning manual before installation
Download the commissioning manual for the specific inverter model and confirm you can access and modify the protection settings. Some inverters lock protection settings — verify you have the installer password or tool needed to access the grid protection parameters. If the settings are locked and cannot be changed to NRS 097 values, the inverter is not usable for South African SSEG.
Document all settings during commissioning
Record every protection parameter in the commissioning report: over/under frequency thresholds, over/under voltage thresholds, reconnection delay, anti-islanding mode, and power factor setting. The commissioning report is submitted to the network operator as part of the as-built documentation. A comprehensive commissioning report reduces the likelihood of additional queries from the network operator.
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Medium Voltage Systems (NRS 097-2-3)
For SSEG systems connecting at medium voltage (typically above 75 kVA or systems requiring MV connection), the relevant standard is NRS 097-2-3. Medium voltage SSEG requires:
- Dedicated protection relay (not just inverter-integrated protection)
- Power system study for protection coordination
- NERSA or Eskom distribution engineering approval
- Directional over-current and earth fault protection
Systems in this category generally require the involvement of a Professional Electrical Engineer registered with ECSA.
Frequently Asked Questions
Is NRS 097-2-1:2024 the same as the European EN 50549? They address the same fundamental concern — safe grid integration of distributed generation — but they are separate standards with different threshold values. South Africa developed NRS 097 independently to reflect Eskom’s specific grid characteristics, particularly the historical frequency excursion behaviour and voltage profiles of the South African network. Do not configure an inverter to EN 50549 settings for a South African SSEG installation.
My inverter was accepted under the 2017 edition of NRS 097. Does it need re-testing for the 2024 edition? Contact your network operator to confirm their acceptance policy for certificates issued against the 2017 edition. Some network operators continue to accept valid 2017-era type-test certificates if the protection settings meet the 2024 requirements. Others require a 2024-edition certificate for new SSEG applications. Do not assume continued acceptance without confirmation.
Where can I purchase NRS 097-2-1:2024? The standard is available for purchase from the South African Bureau of Standards at sabs.co.za. It is also available through the SANS portal. It is not freely available — it is a paid standard.
See the full South Africa compliance guide or the Eskom SSEG registration guide for the complete application process. Use solar software that supports South African system documentation requirements.
