Planning smart lighting in a villa before the plaster goes on

First fix decides most of a lighting system. Cable routes, the number of switched circuits, where the drivers sit and whether a control pair reaches every fitting are all settled before the plaster goes on. The luminaires get chosen later. That order is backwards. It is why a villa ends up with dimming that dies at the bottom of its range, or scenes that cannot change without opening a ceiling.

Two control methods cover most residential work: DALI, standardised as IEC 62386, and the analogue input marked DIM+ and DIM-, which accepts 0-10 V. They place different demands on first fix. DALI needs one pair that reaches every driver, every wall plate and every sensor. The analogue input needs a separate pair for each dimming channel, and the number of channels is frozen the day the conduit is capped.

The control pair, and why it counts as a mains circuit

The DALI Alliance publishes the wiring limits plainly. Each subnet takes 64 control gear and 64 control devices. Bus power supplies provide typically 16 V and up to 250 mA. The maximum cabling length, measured as the distance between the furthest-apart devices, is 300 m, typically using standard 2-core 1.5 mm² cable. Those figures decide how a plot is divided. A villa with a guard house, a pool plant room and a roof terrace can pass 300 m on one subnet unnoticed, because the limit counts the whole run, not one leg.

Power and data share the same pair, so there is no separate bus cable to pull. Polarity does not matter.

None of that makes the pair harmless. On the Mean Well ELG-150 series the terminals are listed as "DALI Interface (primary side; for DA-Type)". They sit on the mains side of the driver's isolation barrier. Route and insulate the bus on that basis.

The analogue input, and the count you cannot change later

On both the Mean Well LCM-25 and ELG-150 series the same terminal pair accepts one of three things: 0 to 10 VDC, a 10 V PWM signal between 100 Hz and 3 kHz, or a resistance. The driver itself supplies the current, 100 µA typical on both series. Polarity is marked and has to be respected.

The resistance table on those datasheets shows what the analogue input really is. Values run from 10K/N to 100K/N, N being the number of drivers dimmed together. Every driver on the pair moves as one. There is no address. Adding a separately dimmable group later means a new pair back to the control position, which is a chase, not a commissioning job.

The bottom of the range is set by the driver. On the LCM-25 the minimum dimming level is about 6 per cent, and the datasheet states that output current is not defined below it. On the ELG-150 the figure is about 8 per cent, and under DALI control the first step is fixed at 8 per cent of output. Output reaches zero only at about 0 kΩ, 0 Vdc, or a 10 V PWM signal at 0 per cent duty cycle. Show a client those numbers before the fittings are ordered.

Breaker allocation follows inrush, not load

Lighting circuits are usually counted in watts. LED drivers break that habit. What trips the breaker at switch-on is the cold-start inrush, not the running load. Both datasheets state the figure, then state, per NEMA 410, how many units may share one 16 A breaker at 230 VAC.

Two products from one manufacturer, the same breaker, a factor of eight between them. Three ELG-150 drivers on a type B breaker is very little lighting for one circuit. A type C breaker doubles the allowance, a choice made on the board schedule, before anybody has picked a driver. Where the fittings are unspecified, allocate circuits against the worst inrush the design might land on, and leave spare ways.

Driver position is a thermal decision

Every driver carries a tc point, a marked spot the manufacturer measures against. The ELG-150 gives a maximum case temperature of 90°C and a working range of -40 to +90°C at the case. The LCM-25 gives 85°C maximum and -30 to +85°C. Those are the limits at which it still functions. The figure that governs its life is lower.

Ten degrees on the case separates a driver with a published life expectancy from one the manufacturer makes no such claim about. A sealed void above an insulated slab, in a hot climate, is not a neutral place for one. Access is the second half of the same decision. Drivers that implement DALI Part 253 report operating time, start counter, supply voltage and frequency, power factor, temperature and output current. A driver that reports its own temperature helps nobody if reaching it means cutting plaster.

One line in both datasheets affects the circuit design directly: to meet the ErP regulation for lighting fixtures, the power supply "can only be used behind a switch without permanently connected to the mains". There has to be a switching device upstream. Decide what that device is, and where it lives, alongside the driver position.

Scenes are software, circuits are not

Scene levels live in the control gear. Each item of DALI control gear holds 16 scenes, and the protocol provides 16 groups alongside its 64 addresses. Devices can be addressed individually, by group or by broadcast, and the benefit worth repeating to a client deciding whether to pay for a bus is this: the lighting system can be reconfigured by software reprogramming, without the need to change the wiring.

That sentence is the whole commercial argument. A scene that turns out wrong after the family moves in is a commissioning visit on DALI. On separate analogue pairs it can be a rewire, and by then the ceiling is closed and painted.

Tunable white changes the cable to the fitting

Colour control sits in Part 209 of IEC 62386, device type 8. It covers Tc, moving correlated colour temperature along the black-body line; xy chromaticity from the CIE 1931 diagram; and RGBWAF for up to six channels. DALI-2 certification for tunable white became available in February 2020, with RGB and multi-type following in September 2021.

In a villa this usually means two LED channels in each fitting, warm and cool. Whether those run from one DT8 driver or from two drivers on separate addresses changes the cores pulled to the fitting and the space needed at the driver. Decide it before the conduit is capped.

Wall plates and sensors take addresses too

Input devices have their own parts in the standard: 301 for push buttons, 302 for absolute input devices, 303 for occupancy sensors and 304 for light sensors. They are multi-master, and up to 32 instances can sit in one product using a single address. A six-button plate is one address, not six. The bus still has to reach every plate and sensor position, including the corridor nobody has thought about.

Fix these on the drawing

• Bus continuity to every driver position, wall plate and sensor, with the 300 m limit measured device to device, not leg to leg.
• A spare draw wire in every conduit run into a ceiling void.
• Driver positions with permanent access and room for the case you might actually fit. An ELG-150 is 219 x 63 x 35.5 mm.
• Circuit allocation taken from the inrush figure of the intended driver, with spare ways left in the board.
• Cores to every fitting that may become tunable white, decided before the ceiling closes.
• An upstream switching device for each driver, as the datasheets require.

This is general information about how the standards and the hardware behave. Electrical design and installation should be carried out by a qualified engineer working to the rules in force where the villa is being built.

Before the ceiling closes, walk the drawing with a measuring wheel and total the bus device to device rather than room to room. If the answer sits anywhere near 300 m, split the subnet while splitting it still costs nothing.