Overview
For storefront LED displays, two common wiring methods are the straight-line ("I") configuration and the T-shaped configuration. Many advertising installers do not understand basic electrical principles and tend to use the straight-line method. This wiring is simple: arrange the switching power supplies in a line and power them on.
Voltage Drop and Cable Load
If the incoming power cable is too long, voltage drop increases and the risk of cable overheating or fire also rises. Based on LED display power consumption and cable calculations, a 2.5 mm2 copper power conductor has a safe continuous current rating of about 28 A. Using 200 W switching power supplies as an example, one 2.5 mm2 feeder could theoretically serve up to 30 supplies in a straight-line layout. In practice, using up to 24 units is recommended.
With 30 supplies laid out in a line and approximately 1 m of cable between each unit, the daisy-chained cable from the 220 V input to the last supply totals about 29 m. Measured at the last supply, the voltage can drop to around 200 V. The cable segment nearest the last supply carries only one 200 W load, while the first segment from the mains carries the load of the remaining 29 supplies, equivalent to about 5.8 kW. If users save cost by using non-standard cable or downgrading to 1.5 mm2 cable, the safety risk is significant. For installations with many power supplies, the T-shaped wiring method is recommended.
T-Shaped Wiring Summary
Wiring summary: bring the 220 V input in at the middle of a run of 30 switching power supplies, with 15 units on each side. Fifteen 200 W supplies total 3 kW, resulting in a cable current of about 13.6 A. A 1.5 mm2 cable is sufficient for that current, and the voltage drop described above will not occur. This method improves safety and reduces voltage drop. When sizing power and cables, do not use the power supply maximum rated output as the continuous design load.
