TNB Compact Substation for a Factory in Rawang or Serendah: When You Need One and What to Check

Key Takeaways

• A TNB compact substation (CSU) is a factory-built, fully enclosed 11kV to 400V unit on a concrete plinth. TNB has treated it as its standard substation for new developments since 2016, and for industrial users it goes up to 1,000 kVA (TNB CSU guidelines).
• The trigger is maximum demand above 350 kVA, about 505A at 400V. Above that, TNB's handbook requires supply by direct underground cable from a new substation (ESAH 3.1). Between 100 kVA and 350 kVA, TNB decides after a system study.
• The land is the owner's job. The standard CSU plot is 5m x 7m, handed to TNB by transfer or lease at a nominal RM10. For applications after 22 November 2024, TNB builds the plinth and installs the unit at its own cost.
• TNB may use your substation to supply other consumers, and a fenced factory's substation should sit at the front with its own access, separate from the factory's main gate (TNB Substation Design Booklet).
• Plan the time. TNB's typical lead time for 400V supply with a new substation is 3 to 12 months, provided council approvals are not delayed.

What is a TNB compact substation, and why do factory owners keep hearing about it?

A compact substation unit is a pre-fabricated, fully enclosed substation that combines the transformer, switchgear and low-voltage feeder pillar in one transportable unit. TNB says it saves space, civil work and installation time compared with a substation building, and its CSU guidelines state that it has been considered the standard substation for new development projects since 2016. TNB's Substation Design Booklet, Edition 2.0 (2024) goes further: the compact type should be the first choice among 11/0.4kV substations for domestic, commercial and industrial development alike.

In practice that means the green or grey kiosk you see near the gate of many newer factories in Rawang and Serendah. If you are building on industrial land, or asking TNB for more power at an existing factory, there is a good chance a compact unit is what TNB will offer you.

When does a factory need its own compact substation?

TNB plans supply around maximum demand (MD), the highest load your factory draws. Table 3-1 of the Electricity Supply Application Handbook (ESAH 3.1) sets the minimum supply scheme for each band. Buyers and tenants usually talk in amps, so the amps below are worked out at 400V three phase (amps = kVA x 1,000 / (1.732 x 400)).

Maximum demand	Roughly in amps at 400V	What TNB's handbook sets as the minimum scheme
Above 12 kVA to 100 kVA	Up to about 144A	Cable from the existing low-voltage network, subject to TNB study
Above 100 kVA to 350 kVA	About 145A to 505A	Cable from a feeder pillar or a new or existing substation, subject to TNB study
Above 350 kVA to 1,000 kVA	About 505A to 1,440A	Direct underground cable from a new substation
1,000 kVA and above	Above about 1,440A	11kV supply through a TNB switching station; you own the transformers

So the compact substation question sits mainly in the 350 kVA to 1,000 kVA band. A factory that needs 800A works out at about 554 kVA, inside that band. A compact unit tops out at 1,000 kVA for commercial and industrial development, and TNB adds a condition: a metering kiosk of matching size must be available for a single-customer connection. Above 1,000 kVA (850 kW), TNB's Connection Charge Book 2025 says supply must be taken at medium voltage, which is a different project.

To turn a machine list into kVA and amps before you talk to anyone, FactoryHub's factory power calculator is a quick start. For the full range of substation types and building sizes, see FactoryHub's TNB substation guide.

Who gives the land, who builds what, and what does it cost?

This is where most surprises come from. TNB's CSU guidelines split the work by application date:

• Applications submitted before 22 November 2024: the developer or user hands over the land and builds the CSU plinth and its accessories; TNB installs the unit.
• Applications submitted after 22 November 2024: the developer or user hands over the land through the proper legal process; TNB builds the plinth and accessories and installs the CSU, with all related costs borne by TNB.

The owner's side of the job is still real work. According to TNB, the applicant must identify a 7m x 5m site agreed with TNB, get planning permission or other authority approval for it from the local council or land office, mark the boundary on the ground, make sure the site is free of legal issues, encroachment and existing utilities (verified by a licensed land surveyor), make the land and access road ready, and submit a soil investigation report certified by a competent engineer.

The ESAH lets the substation land go to TNB by transfer or lease at a nominal RM10. If the land title has not been issued, the applicant gives TNB a bank guarantee for 12 months, renewed until the transfer or lease is registered. The Connection Charge Book adds that where the title is not yet issued, TNB's cost of getting the land through alienation is borne by the consumer or developer, and if owner and TNB cannot agree on the land, its cost is set under the Electricity Supply Act 1990.

Connection charges for a 400V factory with current transformer metering start at RM4,050 for 61 to 90 kW and reach RM38,250 for 721 to 850 kW. Those rates apply where the substation land is handed over or leased at RM10, or no substation is needed, and where the supply source is within 6km.

Where on the lot does the compact substation go?

TNB's Substation Design Booklet gives siting rules that matter when you lay out a factory or judge an existing one:

• For a fenced factory, the substation should be at the front of the factory area, with an access gate different from the factory's main entrance.
• The site must be at least 300 mm above flood level for drainage.
• Keep it at least 15m from refuse areas, and away from a sewage treatment plant (100m from an STP boundary, or 15m where the substation serves the STP or a small shared development).
• Avoid monsoon drains or drains deeper than 1.0m in front of it, so outgoing cables can keep their bending radius.
• Avoid hill edges and slopes, following the federal planning guidelines for hill and highland areas.

The hill and slope rule is worth a thought on undulating land in Serendah and Batang Kali, where a level platform at the front of the lot may already be planned for the guardhouse or truck queue. TNB also says compact units are not used where a circuit breaker installation is needed for important or sensitive premises, where there are more than two 11kV feeders, or in MSC status areas; those cases need an indoor substation building.

What do I check when a factory already has a compact substation?

When I view a factory with a client who needs real power, the substation is one of the first things I look at, because it says a lot about what the building can do. My checklist:

1. Is the substation inside the lot or outside it? A kiosk inside the fence usually means the land was handed to TNB, so the title or a separate lot may show it. Ask the lawyer to check the title and any lease registered to TNB.
2. Who else does it feed? The ESAH states that TNB has the right to use the substation to supply other consumers, so a unit on your lot is not reserved for you.
3. What did the factory actually draw? Ask the owner for recent TNB bills showing maximum demand, and look at the main switchboard rating and the current transformer ratio on the meter. TNB's charge book pairs each load band with a CT ratio, for example 800/5 for 361 to 480 kW.
4. Is there headroom? A compact unit stops at 1,000 kVA. If your plan is well above the current supply, ask an electrical consultant engineer before you sign, because the next step may be 11kV supply and your own switchgear.
5. Access and flooding. Check the TNB gate and the ground level around the kiosk, since TNB needs to reach it and the booklet asks for 300 mm above flood level.

For any load above 100A, TNB requires the application to go through an Electrical Consultant Engineer registered with the Board of Engineers Malaysia. As a tenant, remember that the substation land must come from the registered owner, so a power upgrade that needs new substation land needs the landlord's agreement in writing before anyone applies.

How long does it take, and how does it fit a build or an upgrade?

TNB's handbook gives typical lead times of 3 to 12 months for 400V supply with a substation, less than 3 months without one, and 6 to 12 months for 11kV, all provided there is no delay in local authority approvals. The steps run from the consultant's application and TNB's work plan, through payment of connection charges, to site works, substation energising and meter installation by your electrical contractor.

For a new build on industrial land in north Selangor, I suggest the substation site is fixed on the layout plan before building plans go in, so the CSU approval runs alongside your planning permission instead of after it. My guides on Rawang or Serendah for a new factory and building a factory in Rawang or Serendah cover the other approvals and the insurance during construction. Registered prices for land and factories in each area are on FactoryHub's transactions page.

If you are weighing a factory in the north Selangor corridor and power is the deciding point, send me your load and I will check what each shortlisted unit already has.

WhatsApp Jason Low, Probationary Estate Agent PEA 1478 with CID Realtors Sdn Bhd, on +60 12-288 1834.