I measure a DALI voltage but communication is unreliable, how do I fix it?

Why voltage alone is not enough

A DALI line can show a correct idle voltage of around 16 V and still fail to communicate reliably. Voltage tells you the bus power supply is alive, it does not tell you whether the line can carry the modulated low-level signal that DALI uses to transmit data. Reliability depends on signal margins, current headroom, and the integrity of the wiring, all of which can degrade silently while the multimeter still reads fine.

The three usual causes

Most reliability problems on a powered bus come down to one of three things. First, more than 64 devices on a single line. The DALI standard hard-caps a line at 64 short addresses, and exceeding that, even with input devices that do not count themselves, overloads the supply and corrupts framing. Second, excess current draw from incorrect wiring, typically mains crossed with DALI, water in a junction box, or a faulty device pulling the line low. Third, an undersized or aging bus power supply that cannot hold the line during heavy traffic.

How to isolate it

Disconnect branches of the installation systematically and check whether communication improves after each step. Start with the longest run or the branch with the most devices. The branch that restores reliability contains the fault, and from there you can sub-divide until you reach the individual device or junction.

How ProbitSite pinpoints it

ProbitSite's signal-quality measurement reports the actual high and low signal levels on the line, not just the idle voltage, so you can see immediately which segment or device is dragging the bus down. The green / yellow / red rating maps directly to DALI-2 timing tolerances, so you do not have to guess which branch to chase or replace devices on suspicion.