DALI Installation: Bus Power, Cabling and Commissioning
DALI’s wiring rules are far more relaxed than DMX’s, which makes installation easy and carelessness tempting in equal measure. When a DALI line does not work, the cause is almost always one of three things: insufficient bus power, too many devices, or the wrong cable.
In short
- Bus power is capped at 250 mA and each driver draws 2 mA — do the sum first.
- Cable must be mains-rated; size is chosen to keep voltage drop under 2 V.
- 1.5 mm² reaches roughly 300 m. Screening is not required.
- Topology is free; only a ring is forbidden, and no terminator is needed.
- Mains on the DALI pair destroys every driver on the line — label and measure.
- Always back up the commissioning file and set the system failure level deliberately.
Bus power: calculate this first
A DALI line needs its own power supply. The limits in the standard are clear:
- Bus voltage 9.5 – 22.5 V DC (typically 16 V).
- Total current available on the line: 250 mA maximum.
- Each item of control gear (driver or ballast) draws 2 mA maximum.
- Control devices such as sensors and panels draw more — check the datasheet.
The sum is simple but frequently skipped:
48 drivers x 2 mA = 96 mA 4 sensors x 8 mA = 32 mA 2 wall panels x 10 mA = 20 mA ------------------------------------ total = 148 mA -> within the 250 mA limit
How undersized power shows itself
The line does not die outright, which makes diagnosis harder. Instead the system becomes erratic: some luminaires ignore commands, devices appear and vanish during commissioning, or the bus collapses when everything is addressed at once via broadcast. Symptoms that worsen as the system grows almost always point at the power supply.
Choosing cable
Although the DALI bus is low voltage, in practice it runs in the same containment as mains cable, so it must use mains-rated insulation. Most installations simply dedicate two cores of a standard three-core mains cable to DALI.
The only criterion driving conductor size is keeping the voltage drop below 2 V across the line:
| Conductor size | Approximate maximum run |
|---|---|
| 0.5 mm² | ~100 m |
| 0.75 mm² | ~150 m |
| 1.0 mm² | ~200 m |
| 1.5 mm² | ~300 m (the standard’s upper limit) |
Screened cable is not required. At 1200 bit/s with Manchester coding the signal is already noise-tolerant. If you do use a screen, earth it at one point only.
Topology: almost anything goes
Star, tree, bus or any mixture is allowed. The only prohibition is a ring. No terminator is needed.
Polarity does not matter on most devices, so reversing the two conductors causes no harm. Even so, keeping a consistent colour convention throughout the installation makes future maintenance far easier.
The expensive mistake: mains on the DALI pair
When 230 V and DALI share a multicore cable, mixing up the cores at one end instantly destroys every driver on the line. This is the costliest DALI fault in the field.
- Mark the DALI cores with a distinct colour or label at every terminal.
- Measure the bus before commissioning: you should see 9.5–22.5 V DC.
- Measure the line before connecting drivers, not after.
Commissioning
Once wiring is complete the devices have no addresses and respond only to broadcast commands. Addressing is done with a commissioning tool — a USB DALI interface, an application controller or the manufacturer’s software:
- The tool runs a random addressing cycle; every device takes a temporary address.
- Devices are flashed one by one to identify their physical location and reassigned to meaningful addresses (0–63).
- Groups are defined. A luminaire can belong to several groups at once — both “perimeter” and “open office”, for example.
- Scenes are programmed. Each luminaire writes its own level for each of 16 scenes into its memory.
- Parameters such as fade curve, power-on level and system failure level are set.
- The commissioning file is backed up. Skip this and replacing one driver may mean re-addressing the whole line.
Set the system failure level deliberately
Every DALI device holds a system failure level it falls back to when the controller stops communicating. The default is usually 100%. That may be sensible in a shop; it is not sensible in a hotel corridor at midnight. Decide this value consciously during commissioning.
Going beyond 64 devices
A DALI line carries at most 64 addresses. Larger buildings use multiple lines managed by an application controller or DALI gateway. Split the lines along a sensible boundary — floor, zone or lighting scenario — because groups and scenes cannot cross a line.
Common faults
| Symptom | Likely cause |
|---|---|
| Nothing responds at all | No bus power, or a short on the line |
| Devices intermittently disappear | Undersized supply, excessive run length or voltage drop |
| Commissioning stalls halfway | More than 64 addresses, or a duplicated address |
| Commands randomly delayed | Ring topology, or a second power supply wired in parallel |
| Every driver destroyed | Mains voltage applied to the DALI pair |
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