A DALI communication line runs at ELV – so why do I need to use LV double insulated cable?
The DALI bus voltage (the DALI Line) is in the range 9.5 V dc – 22.5 V dc. This is normally considered Extra Low Voltage, or ELV: a voltage not exceeding 50 V ac or 120 V ripple free dc.
The DALI standard requires only Basic Isolation between Mains (Low Voltage – LV) and the DALI electronics within the control gear.
When the DALI control gear is in a Luminaire, the internal wiring – both DALI and mains power – normally uses single insulated cables.
These two practices make many aspects of installation easier, but they also mean that there is no double insulation and DALI can’t be considered Safety Extra Low Voltage (SELV).
From an electrical safety perspective: DALI Line signals should be treated as mains (LV).
This leads to some interesting situations:
- A DALI Line can be run in the same tray, bundle and conduit as LV wiring.
- Segregation practices when wiring DALI to Control Gear can be the same as mains wiring.
- If using a DALI switch to control lighting, the switch plate needs to be kept the same distance from baths, sinks, showers etc as a normal mains switch.
Also: Every DALI line needs a DALI Power Supply, and these are specialised products. Those DALI power supplies need to internally have only single isolation between mains and DALI. DALI power supplies are not all created equal, and high quality power supplies take a conservative design approach by using double insulation. However from a safety point of view – and in spite of your selection of DALI power supply manufacturer – always assume that single insulation faults in a DALI power supply or anywhere else can result in the DALI line being at live mains potential.
Summary: For proper electrical safety when working on a DALI Line: isolate the DALI power, and the lighting circuit to that particular luminaire and also all the lighting circuits to any of the (up to) 64 DALI Control Gear that are on the same line. This might apply for example when fixing a broken connection or replacing a luminaire or DALI Control Gear.