Downlight Wiring Diagram
This is a free printable downlight wiring diagram: download the diagram as SVG or open it and print to paper or PDF.
A downlight wiring diagram shows how to connect recessed ceiling lights in a loop or radial circuit, covering both mains-voltage LED downlights and transformer-fed low-voltage fittings.
Downlights are recessed luminaires installed flush or near-flush with the ceiling surface. They are among the most common domestic and commercial lighting fittings, but their installation involves several electrical and building fabric considerations that are specific to this type of fitting.
The two main circuit configurations used for downlights are the radial circuit and the loop-at-the-fitting (looped) arrangement. In a radial circuit, the supply cable runs from the ceiling rose or junction box to the first downlight, then on to the next, and so on, in a daisy-chain sequence. In a looped arrangement, each fitting has its own dedicated cable run back to the distribution board or a central junction, but this is less common in domestic installations. The most frequent arrangement in practice is the looped-at-the-fitting method: one cable arrives carrying live, neutral, and earth; a second cable departs to the next fitting using the same conductors. The live conductors are joined with a connector, then routed through the switch before returning as a switched live to the fitting.
Mains-voltage LED downlights (230 V AC in the UK/Australia/EU; 120 V AC in North America) connect directly to the supply without a transformer. Low-voltage downlights (12 V AC or DC) require a driver or transformer, either integral to the fitting or mounted above the ceiling. Integral drivers simplify installation and are the norm for modern LED downlights. External drivers or transformers need adequate ventilation in the ceiling void.
Fire-rated downlights are critical when installed in a floor/ceiling assembly or in a ceiling below a habitable space above. A standard downlight creates a hole in the fire-separating element of the ceiling. Fire-rated fittings are tested to maintain the fire rating of the ceiling assembly for a specified period. Using non-fire-rated fittings in these locations is a building code violation in most jurisdictions.
Insulation contact (IC) and air-tight (AT) ratings are also critical: standard downlights cannot have thermal insulation placed over them, as this causes the fitting to overheat. IC-rated fittings are designed and tested to allow insulation contact. Consult your local electrical code and have the installation performed or inspected by a licenced electrician.
How to wire downlight wiring diagram
- Plan the layout and circuit Mark downlight positions on the ceiling according to the room dimensions and the light distribution angle of the chosen fittings. For a standard 38° beam angle, a spacing of 1.0–1.5 m from walls and 1.0–2.0 m between fittings is typical in rooms with 2.4 m ceiling height, though this varies with the fitting's lux output. Confirm the circuit breaker rating, existing cable size, and how many fittings the circuit can accommodate.
- Isolate the circuit and verify dead Switch off the circuit breaker for the lighting circuit and lock it if possible. Use a non-contact voltage tester at the switch position and at the ceiling rose or existing fitting to confirm all conductors are de-energised. Do not touch any wiring before confirming zero voltage.
- Cut the ceiling holes and run cables Use a hole saw or jab saw to cut holes to the downlight's specified cutout diameter — check the fitting's installation sheet. Before cutting, check above the ceiling with a torch or borescope to confirm there are no structural elements, pipes, or existing cables in the cutting path. Run the cable from the switch position to the first fitting location and between fitting locations. Fit cable to the ceiling joists with cable clips at maximum 400 mm centres in the ceiling void.
- Connect the switch At the switch, connect the incoming permanent live to the switch's line terminal, and the switched live to the load terminal. Where older switch loop wiring (two-core cable with no separate neutral) is used, re-identify the white wire used as the switched live with red or brown tape. In new installations, the switch must be supplied with a three-core cable (line, neutral, and earth) to provide a neutral for smart switches.
- Wire the first downlight In the first fitting's ceiling hole, connect the incoming supply conductors to the fitting's terminal block or connector. Connect the outgoing cable conductors (line, neutral, earth) at the same connector block so the supply is looped through to the next fitting. Earth conductors must be connected to the earth terminal of every metal fitting. For fittings with integral terminal blocks, use the connection method specified in the fitting's instructions.
- Wire subsequent downlights in the loop Each subsequent fitting receives the supply looped from the previous fitting and passes it on to the next one, until the final fitting in the chain. The final fitting receives the supply but has no outgoing cable to the next fitting. All intermediate earth conductors must be jointed and connected. Ensure all connector blocks are fully closed and no bare conductors are exposed.
- Restore power and test each fitting Switch on the circuit breaker. Operate the switch and verify all downlights illuminate. If any fitting fails to light, switch off, check the connector block connections at that fitting, and verify the terminal block is properly closed. For dimmable fittings, test the full dimming range to check for flicker or incompatibility with the dimmer switch.
Specifications
| Typical cutout diameter (UK/AU standard downlight) | 70–90 mm (verify against individual fitting specification) |
|---|---|
| Supply voltage (UK / AU / EU) | 230–240 V AC, 50 Hz |
| Supply voltage (North America) | 120 V AC, 60 Hz |
| Minimum cable size (UK/AU lighting circuit) | 1.0 mm² (permitted in some regulations) — 1.5 mm² recommended |
| Typical ceiling cutout clearance from joists | Minimum 50 mm from the edge of any joist |
| Minimum IP rating (domestic bathroom zone 1) | IPX4 (splash proof) — verify against local standard |
| Fire resistance period (fire-rated downlights) | 30 min or 60 min depending on the floor/ceiling assembly rating |
| Applicable standards | IEC 60598 (luminaires), BS 7671 (UK), AS/NZS 3000 (AU/NZ), NFPA 70 (USA) |
Safety warnings
- Electrical installation work including adding or rewiring downlights must comply with your local electrical code. In the UK, fixed electrical work in dwellings requires notification under Part P of the Building Regulations and must be either performed by a competent person registered under a government-approved scheme or notified to and inspected by your local building authority. In Australia, all electrical work must be performed by a licenced electrician.
- Always isolate the circuit at the distribution board and verify all conductors are dead with a non-contact voltage tester before touching any wiring or cutting any ceiling holes. This applies even if the switch is in the off position — the permanent live conductor at the ceiling is always energised regardless of switch position.
- Use fire-rated downlights in any ceiling that forms part of a fire-compartment boundary, including ceilings between floors in multi-storey buildings, and ceilings between habitable rooms and garage spaces. A non-fire-rated fitting creates a breach in the fire barrier.
- Never place thermal insulation in direct contact with or over a non-IC-rated downlight. Overheating of the lamp, driver, or fitting body is a fire hazard. Ensure the installed fitting has an IC rating before allowing insulation contact.
- Downlights in bathrooms and other wet areas are subject to IP (Ingress Protection) rating requirements that specify the minimum dust and moisture protection for each zone. Refer to IEC 60529, BS 7671, or AS/NZS 3000 for zone requirements and ensure the fitting is rated accordingly.
Tools needed
- Non-contact voltage tester
- Hole saw (diameter matched to fitting's cutout specification)
- Flat-head and Phillips screwdrivers
- Cable strippers
- Wire cutters
- Borescope or inspection torch (for checking above ceiling before cutting)
- Circuit tester or multimeter
- Cable clips and hammer or staple gun for cable securing
Common mistakes
- Cutting ceiling holes without checking for cables, pipes, and structural elements above — always use a borescope or inspection torch before cutting.
- Using non-fire-rated fittings in a fire-compartment ceiling — this is a building code violation and a life-safety issue. Check the fitting's fire rating before purchase.
- Placing insulation over non-IC-rated downlights — overheating causes premature lamp failure and presents a fire hazard. Only use IC-rated fittings where insulation contact is possible.
- Not re-identifying the white switched live conductor in a switch loop — the white conductor used as a live must be marked with brown or red tape at both ends to indicate it is not a neutral.
- Connecting more fittings to a circuit than the cable and breaker can handle — calculate the total load (watts) and divide by the supply voltage to get amperage. Do not exceed 80% of the circuit breaker's rating for continuous loads.
- Installing a leading-edge (trailing-arm) dimmer switch designed for halogen lamps with LED downlights — this causes flicker, buzzing, and premature driver failure. Use a dimmer specifically designed for LED loads.
Troubleshooting
- One or more downlights in a loop fail to illuminate
- Cause: Open circuit in the supply loop, either a failed connector at one fitting or a break in the cable between fittings Fix: Isolate the circuit. Start from the last functioning fitting and test continuity forward. Check that all push-fit or screw connector blocks are fully closed. A single loose connection breaks the supply to all fittings downstream of that point in the loop.
- Downlights flicker or buzz when dimmed
- Cause: Dimmer is incompatible with the LED driver type, or the minimum load requirement of the dimmer is not met Fix: Check the dimmer's specification for LED compatibility and minimum load rating. Replace with a dimmer designed for LED loads. If the total wattage of the fittings is below the dimmer's minimum load specification, add an LED dummy load module or select a dimmer with a lower minimum load rating.
- Circuit breaker trips when all downlights are switched on
- Cause: Total load exceeds the circuit breaker rating, or there is a wiring fault causing an overload or short Fix: Calculate the total connected wattage and compare to the circuit capacity. If the load is within rating, an intermittent short circuit is likely the cause. Isolate the circuit, disconnect all fittings, and restore power to check if the breaker still trips. If it does, the fault is in the fixed wiring. If not, reconnect fittings one at a time to identify the faulty fitting.
- Downlight operates but LED module runs excessively hot
- Cause: Insulation is covering the fitting, there is inadequate ventilation in the ceiling void, or the driver is incompatible with the LED module Fix: Remove any insulation in contact with non-IC-rated fittings. Ensure fittings have adequate clearance for convective cooling. If the heat is coming from the driver, verify the driver's output current matches the LED module specification. Replace a failed or incompatible driver.
Frequently asked questions
Do I need fire-rated downlights?
Fire-rated downlights are required wherever the ceiling forms part of a fire-separating element — typically between floors in a multi-storey building, or between a habitable room and a roof space that could allow fire to spread. In many jurisdictions, fire-rated fittings are mandatory in these locations under the building code. Check your local building regulations and consult an electrician or building inspector.
Can I put thermal insulation over downlights?
Only if the downlight is rated for insulation contact (IC rating). Standard downlights must have a minimum clearance of 75–100 mm from insulation on all sides, and insulation must not be placed over the top of the fitting. Installing insulation over a non-IC-rated fitting creates a fire hazard from overheating. Modern LED downlights with integral drivers often have an IC-AT rating — check the fitting's datasheet.
What is the maximum number of downlights on one circuit?
This depends on the circuit breaker rating, cable gauge, and the wattage of the fittings. On a 6 A lighting circuit (UK) with 5 W LED fittings, the theoretical maximum is very high, but circuit designers typically limit each circuit to 10–12 fittings for practical reasons. On a 15 A North American circuit with 10 W fittings, the load limit is 1440 W (80% of 1800 W), allowing up to 144 such fittings — but cable voltage drop should also be checked.
What is the difference between a constant current and constant voltage LED driver?
A constant current driver maintains a fixed output current (for example, 350 mA or 700 mA) and varies voltage to suit the LED load — this is the correct driver type for most LED modules. A constant voltage driver maintains a fixed output voltage (for example, 12 V or 24 V DC) and is used with LED strips or modules designed to regulate their own current. Using the wrong driver type for the LED module will cause premature failure.
Why do my LED downlights flicker when dimmed?
LED flicker on dimming usually has one of three causes: the dimmer switch is not compatible with the LED driver type (leading-edge dimmers designed for halogen lamps often conflict with LED drivers); the minimum load on the dimmer is not met (modern LEDs draw so little power that many dimmers do not function at the bottom of their range); or the LED driver itself is not dimmable. Replace with a dimmer rated for LED loads and confirm the driver is marked as dimmable.