Similar to the 1...10 V interface, DALI is also based on low voltage, which is not implemented as extra-safety low voltage. DALI lines must be mains voltage-stable and can be installed in a joint sheathed cable with the mains voltage line (e.g. NYM, 5-core, see figure). In contrast to the DMX signal, the transmission frequency of the DALI signal is low enough to avoid the need for a terminating resistor or a limitation to line section installation. A 5-core wiring with generally applied cable routing for functional lighting has proven expedient. Line length is limited to 300 m (with 1.5 mm²).
The control power in the DALI system used for operating the control gear units is not provided by the control gear units, in contrast to the 1…10 V interface. Hence, the control gear unit is a passive component and requires control power generated by a DALI power source. Many control devices feature an integrated DALI power source, but it can also be realised as a separate component.
The permissible control power on a DALI line is limited to a maximum value of 250 mA. The control power requirement of connected control gear units is 2 mA per DALI address at maximum. DALI power sources integrated in commercially available control devices usually supply 128 mA or less, which can mean that the number of participants that can be operated in broadcast mode is limited to 64 or fewer. When connecting DALI-2 control components, it may be necessary to consider their control power requirements as well.
Generally, observing polarity is not required when connecting DALI participants to the interface. However, this is left up to the respective manufacture and not part of the definitions of the DALI standard. When operating several DALI-2 control devices in multi master operation in parallel, their interface polarity must generally be observed (see figure).