DALI dimming and wiring

How the system works

DALI carries bus power and digital messages on the same pair. Drivers still need their own power supply and connect to their LED loads separately. An application controller sends commands; switches and sensors provide input. Broadcast can operate without individually addressing every fitting; individual and group control needs commissioning.

DALI: mains power plus bus power

Two functions, not a universal requirement for two independent 230 V circuits. The lighting driver needs its rated power supply (normally 230 V AC in this UK example), while the control interface has a separate function. An electronic controller may also require a permanent 230 V line and neutral, or a specified DC supply; a passive analogue controller may need no separate operating supply. The exact controller instructions decide this.

DALI drivers normally retain permanent mains L and N for commands to work, even when commanded off. The DA/DA bus also needs a DALI bus PSU, typically around 16 V DC, often integrated in a controller. A controller's own operating supply and its bus-PSU function are not the same thing: confirm whether a bus PSU is actually included. Some switches and sensors are bus-powered and need no separate mains feed; other controllers need their own mains or DC supply. Never apply 230 V to DA/DA.

Multiple supplies and emergency fittings

One control group or DALI bus can include equipment fed from more than one mains circuit. Identify and safely isolate every relevant source, including separately powered controllers, bus PSUs and emergency batteries, before working; label multiple supplies and provide the required isolation arrangements. Do not disconnect or bridge control wiring live. Emergency luminaires may require a permanent 230 V charging/monitoring feed as well as a switched maintained-lighting input, depending on the exact product. Do not assume a dimming command or a lighting switch isolates that permanent feed. Follow the emergency gear's wiring and testing instructions.

Bus limits and cable planning

A DALI-2 subnet supports up to 64 control gear and 64 control devices, subject to actual controller capability and bus-current budget. The bus is typically about 16 V, with total maximum PSU current limited to 250 mA. DALI Alliance recommends no more than 300 m between any two devices when using adjacent 1.5 mm² conductors at 250 mA; this is not simply a 300 m total-cable allowance. Check voltage drop, cable characteristics and all manufacturer limits.

Wiring and commissioning sequence

1. 1

   Specify the whole system

   Select DALI-compatible control gear, an application controller, input devices and a bus power supply. The PSU may be integrated in a controller. Check the DALI Alliance product database where certification is claimed; a generic dimmable lamp or a pair of control terminals does not establish DALI compatibility.

2. 2

   Design the bus and supplies

   Connect the bus PSU, controller, input devices and drivers to the same two-wire bus in parallel. A line, star or tree layout may be used within the equipment rules; avoid closed rings. Plan mains power separately for drivers and any externally powered control equipment. Do not join unrelated DALI subnets.

3. 3

   Isolate all associated sources and wire

   Prove dead at the work location after identifying every relevant mains circuit and bus power source. Connect the pair to DA/DA (or the maker's equivalent terminals); standard DALI bus connections are not polarity-sensitive. Use CPC only for protective earthing, never for DA. Follow the actual LED-output polarity and ratings separately.

4. 4

   Check insulation, cable and bus loading

   Standard DALI must not be assumed SELV. Use the insulation and segregation required by the equipment and BS 7671; sharing a suitably rated multicore with mains is conditional, not automatic. Add up device bus-current demand and all PSU maximum outputs. Do not exceed 250 mA total maximum bus supply current.

5. 5

   Test the installation without damaging electronics

   Do not apply an insulation-resistance tester to connected DA terminals, LED outputs or sensitive electronics. Disconnect or protect equipment and choose the test arrangement from BS 7671 and manufacturer instructions. Dead wiring tests and a successful bus scan are different checks; neither substitutes for the other.

6. 6

   Commission and document

   Discover devices, identify which fitting each address operates, allocate short addresses, groups and scenes, then set minimum/maximum levels, fade behaviour, power-on and system-failure levels where supported. Test occupancy/daylight inputs and bus/mains failure behaviour, save the configuration and label circuits and addresses. Emergency lighting needs its own design, commissioning and test regime.

Common fault checks

No response: check driver mains supplies, bus PSU presence, shorts, loading, controller configuration and discovery. A glowing lamp does not prove healthy communications. Wrong group: check addresses and mapping. Unexpected behaviour after a power cut: check configured power-on and failure levels. Do not bridge DA to line or apply mains to a bus-only switch interface; some products have separate mains-rated push inputs, but only their own wiring diagram authorises that connection.

Where it makes sense

Offices, classrooms, corridors and larger residential schemes where scenes, zoning, sensors and future reconfiguration matter. DALI-2 colour-control features depend on the correct device type and controller; ordinary DALI brightness control does not establish tunable-white capability.

Paul's products: do not assume every Kosnic DD lamp, Blanca fitting, BELL tube or Aurora lamp accepts this interface. Confirm the exact driver/module code and accessories first. A Blanca enclosure alone does not determine the dimming system.