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Designing a DALI application
DALI Manual | 08-2013 | en
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Calculating the voltage drop
The formula for calculating the voltage drop is as follows:
U
v
Voltage drop in V
I
Current in A (0.25 A)
S Cross section in mm
2
l
Cable length in m
γ Electrical conductivity in m / (Ω mm ),
2
for copper cable: 56 m / (Ω mm )
2
Example: DALI circuit with a cable length of 300 m and a cable cross-section of 1.5 mm²
Exact result:
This example shows that:
Rule of thump:
As it is somewhat tricky to calculate the cable length based on the voltage drop the rule of thumb is as follows:
I NOTICE
The maximum current of 250 mA must be used for calculating the voltage drop.
for a cable length of 300 m the voltage drop along the cable is 1.786 V
a further voltage drop of 0.214 V is available for terminal points (contact resistance)
If a cross-section of 1.5 mm² is used, the maximum cable length is 300 m.
If a smaller cross-section is used the possible cable length is reduced accordingly.
I NOTICE
Tridonic recommends always using a cable cross-section of 1,5 mm² for DALI control lines.