Residential · TNB supply
Upgrading from Single-Phase to Three-Phase TNB Supply: When You Need It, Costs and Steps
More Malaysian homes are hitting the limits of single-phase supply: more aircond units, instant water heaters, induction hobs and now EV chargers. This guide explains how to tell whether you need three-phase, what TNB charges, and what the contractor does.
Single-phase or three-phase: what is the difference?
| Single-phase | Three-phase | |
|---|---|---|
| Wires at the TNB meter | 2 (one live, one neutral) | 4 (three live, one neutral) |
| Voltage | 230 V | 400 V between phases, 230 V to neutral |
| Suitable load (myTNB FAQ) | Up to 10 kW | Above 10 kW, up to 37 kW for homes |
| Maximum demand (ST guideline Table 6.2) | Up to 12 kVA | Above 12 kVA, up to 100 kVA |
| Typical homes | Condos, apartments, smaller terraces | Larger terraces, semi-Ds, bungalows |
Sources: myTNB FAQ; ST GP/ST/No.39/2024, Table 6.2.
Signs you need three-phase
- Your main switch or TNB cut-out trips when several big appliances run together.
- You have, or plan to have, three or more aircond units (TNB's rule of thumb).
- You want an 11 kW or 22 kW EV charger. A 7.4 kW home charger usually works on single-phase. See EV charger installation.
- You are adding an extension, a commercial kitchen, a lift or a pump that needs a three-phase motor.
- Lights dim noticeably when the aircond compressors start.
A registered contractor confirms this with a load calculation: adding up your appliances and applying diversity, to get the maximum demand.
How much does TNB charge?
myTNB publishes worked examples for upgrading an existing single-phase supply to three-phase. The charge is the new three-phase connection fee minus the single-phase fee you already paid:
| Supply type | Calculation | TNB connection charge |
|---|---|---|
| Overhead cable | RM750 (new three-phase) − RM450 (existing single-phase) | RM300 |
| Underground cable | RM1,700 − RM450 | RM1,250 |
Extra works such as horizontal directional drilling are charged separately, and your security deposit is adjusted to the higher supply. Online applications on myTNB are limited to a maximum demand of 60 kW (100 A). Source: myTNB, Upgrade or Downgrade Electricity.
What the electrical work costs
The TNB charge is only part of the total. Inside your home, the contractor must:
- Install a new three-phase meter board for TNB's meter.
- Replace your DB with a three-phase (TPN) distribution board, with circuits balanced across the three phases.
- Upgrade the main incoming cable if needed (ST Table 8.2: 10 mm² up to 40 A, 16 mm² up to 63 A, 25 mm² up to 100 A).
- Test the installation and issue Borang G and Borang H.
| Item | Typical cost |
|---|---|
| TNB connection charge | RM300 (overhead) or RM1,250 (underground) |
| Deposit adjustment | Set by TNB based on your supply |
| Three-phase DB change (Luco Group, standard terrace) | from RM1,880 |
| Meter board, incoming cable, extra circuits | Depends on distance and layout |
Forum users on Lowyat have reported paying separately for a meter board (about RM900) and an agent fee to handle TNB paperwork (RM1,000 to RM1,100) (source). These are anecdotal figures. A registered contractor normally handles the application as part of the job.
For a specific board, price a three-phase TPN DB in our DB & panel configurator.
Step-by-step: how the upgrade works
- Site visit and load calculation by a registered electrical contractor.
- Application on myTNB submitted by the contractor with the load details.
- TNB site check and estimate of charges.
- Payment of the connection charge and deposit adjustment.
- Internal works: new meter board, three-phase DB, incoming cable, circuit balancing.
- Testing and certification: the contractor issues Borang G (supervision and completion) and Borang H (test results).
- TNB installs the three-phase meter and connects the new supply.
How long does it take? There is no official TNB timeline for homes. Installers report anything from 1–3 weeks (Bani Venture) to 2–6 weeks (EvGuru), depending on the area and whether cable works are needed.
Will three-phase increase my electricity bill?
No. Your bill is based on the kWh you use, not on the number of phases. Three-phase only gives you more capacity. See how your TNB bill is calculated.
Who can do the work?
Only an electrical contractor registered with Suruhanjaya Tenaga, with a competent person (wireman) qualified for three-phase work, can do the installation and sign the certificates. A Class C contractor such as Luco Group must employ a PW4 wireman, who is qualified for three-phase installations. Installations above 100 A must be designed by a professional engineer or a registered electrical contractor, according to the ST guideline. How to check a contractor's registration.
Frequently asked questions
Do I need three-phase for an EV charger? Not for a 7.4 kW charger in most homes. You need three-phase for 11 kW or 22 kW chargers, or if the charger pushes your total load above about 10 kW.
Can I downgrade back to single-phase? Yes, TNB handles downgrades through the same myTNB process.
Can I apply to TNB myself? The application needs load details and the contractor's certification, so in practice your registered contractor submits it.
Will my old appliances still work? Yes. Normal appliances still run on 230 V; the contractor spreads the circuits across the three phases.
Sources
- myTNB, Upgrade or Downgrade Electricity (residential). mytnb.com.my
- myTNB, FAQ. mytnb.com.my/faq
- Suruhanjaya Tenaga, GP/ST/No.39/2024, Tables 6.2 and 8.2. st.gov.my PDF
- Lowyat Forum, user discussion on three-phase upgrade costs. forum.lowyat.net
- Bani Venture, Upgrade atau downgrade meter TNB. baniventure.net
- EvGuru, Do you need TNB approval to install a home EV charger. evguru.com.my
This guide is general information, not a substitute for an inspection by a registered electrical contractor. Regulations and TNB charges change; always check the linked official sources.