TNB’s grid connection approval is the second of two mandatory approvals for a Malaysian NEM solar installation — SEDA quota approval comes first, TNB technical approval comes second. TNB’s technical review is more detailed than SEDA’s; it assesses the system’s actual impact on the distribution network. For commercial systems above 75 kWp, TNB’s protection relay requirements and potential request for load flow studies can extend the approval timeline significantly. This guide covers what TNB requires, in what format, and in what order.
Never Energise a Grid-Connected Solar System Before TNB Connection Approval
Energising a solar system connected to the TNB grid without TNB’s connection approval is a violation of the Electricity Supply Act 1990. TNB can disconnect the system, issue penalties, and require the customer to reapply from scratch. The cost and delay of an unauthorised connection far exceeds the time saved by skipping the approval process.
TNB Application Documentation
Document Checklist by System Type
| Document | Residential (≤12 kWp) | Commercial (12–75 kWp) | Large Commercial (>75 kWp) |
|---|---|---|---|
| SEDA NEM Approval Letter | Required | Required | Required |
| PE-stamped SLD | Required | Required | Required |
| Inverter datasheet | Required | Required | Required |
| Panel datasheet | Required | Required | Required |
| Contractor CIDB registration | Required | Required | Required |
| ST Electrical Contractor Licence | Required | Required | Required |
| TNB account details | Required | Required | Required |
| Protection relay schedule | Not required | May be required | Required |
| Load flow study | Not required | Not required | May be required |
| Metering arrangement diagram | Part of SLD | Separate document | Separate document |
Single-Line Diagram (SLD) Requirements
The PE-stamped SLD must show:
- Solar array configuration (number of strings, panels per string, total kWp)
- DC disconnect and protection (DC isolator, DC fuse, surge protection device)
- Inverter (make, model, AC output rating, protection relay functions)
- AC protection (AC isolator, residual current device, over-current protection)
- Bi-directional NEM meter location (metering point at the TNB boundary)
- Main distribution board (MDB) connection and main switch
- Earthing and bonding arrangement (PV array, inverter, MDB)
- Labels and ratings for all components
- For systems above 75 kWp: dedicated protection relay, metering cubicle, point of common coupling (PCC) with TNB’s network
Technical Protection Requirements
Anti-Islanding Protection
All grid-connected inverters must include automatic anti-islanding protection per IEC 62116. The function must:
- Detect loss of TNB supply within 2 seconds
- Automatically disconnect the inverter from the grid upon detection
- Prevent re-connection until TNB supply has been restored and is stable for a defined period (typically 30–300 seconds — confirm with the inverter manufacturer)
Verification during inspection: TNB inspectors simulate a grid outage condition and verify that the inverter disconnects within the required timeframe. Confirm during commissioning that the anti-islanding setting is enabled (some inverters ship with this function disabled by default).
Voltage and Frequency Protection
| Protection Function | Trip Threshold (Peninsular Malaysia) |
|---|---|
| Under-voltage | Disconnect if voltage falls below 87% of nominal (196V for 230V nominal) |
| Over-voltage | Disconnect if voltage exceeds 110% of nominal (253V for 230V nominal) |
| Under-frequency | Disconnect if frequency falls below 47.5 Hz |
| Over-frequency | Disconnect if frequency exceeds 52.0 Hz |
| Reconnection | Only reconnect after supply stable for 30–300 seconds |
These thresholds are the general TNB Distribution Code requirements. TNB’s technical assessment may specify different or tighter thresholds for specific connection points — follow the technical assessment letter for site-specific requirements.
Protection Relay for Systems Above 75 kWp
For commercial NEM installations above 75 kWp, TNB typically requires a dedicated protection relay at the point of connection with the distribution network — separate from the inverter’s built-in protection functions. The protection relay:
- Monitors voltage, frequency, and earth fault conditions at the grid connection point
- Trips the main circuit breaker between the solar system and the TNB network if thresholds are exceeded
- Must be type-approved and settings verified against TNB’s relay setting schedule
- Settings must be documented in the SLD and confirmed with TNB’s protection engineer during the technical assessment
Common approved protection relay types for Malaysian solar installations include numerical protection relays from manufacturers such as Schneider Electric, ABB, SEL, and similar. Confirm the approved relay list with TNB — using an unapproved relay type will delay the connection approval.
Metering Requirements
Bi-Directional NEM Meter
TNB supplies and installs the bi-directional NEM meter as part of the NEM approval process. The customer pays the metering point preparation cost (metering cubicle, wiring to the metering point) but not the meter itself.
For large commercial systems, TNB may require a dedicated metering cubicle with a CT (Current Transformer) metering arrangement — the design of this cubicle must be approved by TNB before installation.
Metering Point Location
The NEM meter must be installed at the boundary between the customer’s installation and TNB’s network. For most buildings, this is at the main incoming supply point (the existing TNB supply meter location). The SLD must clearly show the metering point and confirm that no generation equipment is connected upstream (on the TNB side) of the meter.
TNB Inspection Process
Booking the Inspection
Book the TNB site inspection via the myTNB portal or the regional TNB office after system installation is complete. TNB schedules inspection appointments based on technician availability in the area — advance notice of 2–4 weeks is typical.
What TNB Inspects
| Item | What TNB Checks |
|---|---|
| System capacity | Confirms installed kWp matches approved SLD and SEDA approval |
| Inverter model | Verifies model matches approved documentation and is on ST approved list |
| Anti-islanding | Tests automatic disconnection under simulated grid outage condition |
| Protection relay (>75 kWp) | Verifies relay model, settings, and trip function |
| Metering arrangement | Confirms meter location and that no generation is connected upstream of the meter |
| Earthing | Checks earthing connections at PV array, inverter, and MDB |
| Labelling | Verifies DC and AC isolation points are clearly labelled and accessible |
| AC and DC isolators | Tests operation and confirms accessible location for KPLC technicians |
Inspection Outcomes
| Outcome | Description | Next Step |
|---|---|---|
| Pass | All items comply | TNB installs bi-directional NEM meter; NEM billing begins next cycle |
| Conditional pass | Minor items need correction | Correct items; notify TNB for re-inspection of specific items only |
| Fail | Significant non-compliance | Address all defects; book full re-inspection |
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Common TNB Application Issues
| Issue | Cause | Resolution |
|---|---|---|
| SLD rejected — no PE stamp | Drawing signed by draftsman but not stamped by PE | Engage BEM-registered PE; resubmit stamped SLD |
| Inverter not on approved list | Specified inverter not in ST’s approved equipment register | Check ST approved list before specifying; change inverter model if needed |
| Application held — no SEDA letter | TNB application submitted before SEDA approval | Wait for SEDA Approval Letter; resubmit to TNB |
| Technical assessment requests load flow | System large enough to impact local network | Engage a PE with load flow analysis capability; complete and resubmit |
| Inspection fails — anti-islanding disabled | Inverter shipped with anti-islanding in standby mode | Enable and test anti-islanding during commissioning before booking inspection |
| Meter cubicle design not approved | Large commercial system requires dedicated cubicle | Submit cubicle design to TNB for pre-approval before fabrication |
Related Malaysia Compliance Guides
- Malaysia Solar Regulations Overview — full country compliance stack
- Malaysia NEM 3.0 Guide — quota system and NEM billing mechanics
- SEDA Application Process — SEDA NEM portal steps
- C&I Solar Malaysia — NEM vs SELCO decisions for commercial buyers
Use solar design software with Malaysian irradiance data and TNB-aligned SLD outputs to reduce preparation time for grid connection applications.
Frequently Asked Questions
Does TNB charge a fee for the solar connection application? TNB charges a connection assessment fee for solar applications. The fee structure depends on the system size — residential applications have a lower assessment fee than large commercial applications. TNB may also charge a service fee for the bi-directional NEM meter installation. Confirm current fee schedules with TNB’s regional commercial office, as fees are reviewed periodically and vary by system category.
Can I submit the TNB application before installation is complete? Yes — and this is recommended for commercial systems. Submit the TNB application as soon as you receive the SEDA Approval Letter, even if the installation has not yet started. TNB’s technical assessment process (which can take 10–16 weeks for commercial systems) can run in parallel with equipment procurement and site preparation. This parallelism can save 2–3 months compared to submitting the TNB application after installation is complete.
Who is responsible for the earthing system at the PV array? The electrical contractor is responsible for the earthing system design and installation. The earthing arrangement must be shown on the PE-stamped SLD and must comply with the Electricity Regulations 1994 and MS IEC 60364-7-712. TNB’s inspector will check that the array frame, inverter chassis, and MDB are all properly earthed and bonded. Common issues: PV array frame not bonded to the building’s main earthing system, or undersized earthing conductors.
What happens if I change the inverter model after TNB approval but before installation? Changing the inverter model after TNB connection approval requires notifying TNB and, if the new model is materially different (different protection settings, different AC output), potentially resubmitting the application with an updated PE-stamped SLD. Installing a different inverter model than what was approved without notifying TNB is a compliance violation that can delay the meter installation or trigger re-inspection requirements. Notify TNB proactively of any equipment changes — the cost of transparency is much lower than the cost of a failed inspection.
