What an Installer Needs to Know About Your Electrical Supply Before Solar Design

Inhome Solar home planning note

The first useful conversation is not about squeezing in the maximum number of panels. It is about how a proposed solar system will connect to the electricity supply that already serves the home.

Two houses can have similar roof space and very different electrical arrangements. One may have a normal family load. Another may run several air-conditioners, a water pump, a workshop, an EV charger or a renovation load. The installer needs to see the whole picture before fixing a layout or quotation.

Start with the supply arrangement

TNB's supply application guidance says domestic premises are generally given either a single-phase 2-wire supply or a three-phase 4-wire supply. It also says the actual supply voltage depends on the individual applicant's load requirements.^[20]

For a homeowner, that means the installer should not rely on a guess from a package name or a quick look at the roof. Send the latest bill, tell the team what normally runs in the home, and say whether the supply type is known or still needs to be confirmed. If you have recently added heavy loads, include that change instead of treating the older bill as the whole story.

Future plans belong in the first conversation too. An EV charger, extra cooling, a kitchen extension or a home workshop can change the electrical discussion even when the roof itself stays the same. You do not need to calculate a new solar size yourself. You do need to tell the installer what may be added and when.

Bring the meter and distribution board into view

A bill shows consumption. It does not show the physical route from the incoming supply to the distribution board, the space available for protection equipment or the practical route for solar cables. A few clear photographs taken from a safe position can help the team prepare better questions before the visit.

TNB's metering guidance says the meters used to measure imported or exported electricity are provided and maintained by TNB. It also places responsibility on the customer to keep the point where the supply line terminates accessible to TNB personnel.^[21] That is one reason the meter area should be shown early, especially when a proposed layout may affect access or cable routing.

Inhome Solar's authorised project archive includes close views of an inverter, protective enclosures and a distribution board. The photograph is useful for showing the kind of equipment that may sit beside a solar installation. It does not prove that another home has the same supply, wiring, equipment or available space.

Take the photo from outside the enclosure. Do not remove covers, touch wiring or alter a TNB meter or fuse. If a label is unclear, write "not sure" and let a qualified person check it rather than filling in the gap from a guess.

Ask where the connection work sits

The Energy Commission's June 2026 guideline for solar photovoltaic installation for self-consumption in Peninsular Malaysia says the design, equipment, installation work, testing, commissioning and maintenance of a solar PV installation must follow the relevant Act, Regulations, utility requirements and other applicable rules.^[23]

Within that guideline's scope, the drawings and calculations are to be prepared and certified by a qualified and competent person. The electrical installation work, supervision, testing and commissioning are to be carried out by qualified Electrical Contractors and Competent Persons registered with the Commission.^[23] The Commission's installation page also says contractors and wiremen must hold a valid licence before carrying out electrical installation works.^[24]

Ask the installer to name the party responsible for each part of the work. The proposal should make clear what has been reviewed, what still needs a site check, whether any supply work is separate from the solar installation, and who will handle the required technical documents. A neat roof layout is not enough if the electrical handover is vague.

Supply type is not a system size

TNB's public solar page says its calculator uses the bill or consumption as an input and notes that the final installation size will be determined after a site assessment.^[18] Use that as a useful guardrail. A single-phase or three-phase label can help the installer understand the starting point, but it does not replace a property-specific review of the roof, load, electrical board, protection, cable route and proposed operating method.

Be careful with programme names as well. The June 2026 Energy Commission guideline cited above says it does not apply to premises installed with or applying to install solar PV under the Net Energy Metering Programme or Solar Accelerated Transition Action Programme.^[23] If a proposal follows a named route, ask the installer to state which current requirements apply to that route. Do not copy an old limit or application step from another property.

Send a useful first message

Before the first visit, send the latest TNB bill or bills, a clear photo of the meter area and distribution board, the property type, and a short note about when the home is occupied. Add the main loads that run during the day and at night. Mention any EV charger, renovation, new air-conditioners or other change that may arrive after the solar system.

If you know the home is single phase or three phase, include that information and say how it was confirmed. If you do not know, say so. Honest uncertainty gives the installer something to verify; a confident guess can send the conversation in the wrong direction.

Inhome Solar lists solar consultancy advisory, solar documentation and TNB NEM application, and solar system installation among its public services.^[3] Send the bill, the safe-to-share photographs and the usage note through the solar services page or the Inhome Solar contact page.

This guide helps you prepare information for a solar consultation. It is not a system-size recommendation or a remote electrical assessment. Final design, protection, connection method, installation and commissioning must be confirmed for the individual property by qualified professionals under the requirements that apply to the chosen route.