User Manual

Planning (har
dware)
Power requirements
7
24 | 35 A6V11666339_en--_b
7.4.3 Power requirements for DC 24 V
Operating voltage
The operating voltage is DC 24 V. It must meet the requirements for SELV or PELV per IEC 60364-4-41.
NEC: Class 2 circuits.
Permissible deviation to nominal voltage DC 24 V on the power supply: +15% / -10%.
This guarantees a tolerance of +15/-15% on the devices after considering line and contact resistance (web
server: -20%).
Wire lengths: Power supply DC 24 V
The basis for calculation is the permissible voltage drop off of 2.4 V (10%, web server) or 1.2 V (5%, touch
panels on the power line between the power supply and the farthest power point).
The following tables outline the wire lengths and diameters based on load.
Cross-section/power Cable length DC 24 V – Web server
10 VA 20 VA 50 VA 100 VA 200 VA
2.50 mm
2
/ AWG14
350 m 175 m 75 m 35 m 18 m
1.50 mm
2
/ AWG16
210 m 105 m 42 m 20 m 10 m
1.00 mm
2
/ AWG18
135 m 68 m 27 m 14 m 7 m
Cross-section/power Cable length DC 24 V – Touch panels
20 VA 50 VA 100 VA 200 VA
2.50 mm
2
/ AWG14
75 m 35 m 18 m 9 m
1.50 mm
2
/ AWG16
42 m 20 m 10 m 5 m
1.00 mm
2
/ AWG18
27 m 14 m 7 m 3.5 m
The supply wire (AC 24 V) and return wire (⊥) can each have the indicated lengths.
Each power point is either connected separately to the terminal bar on the power supply (star wiring) or looped.
Power is added together for multiple back-to-back looped devices which reduces the cable length accordingly.
Cables may be wired in parallel to increase the cross section.
In practice, the small level of permissible voltage drop off means that the power supply must always be installed
in close proximity to the devices and that any cascading powering of devices is only possible over short
distances or at small outputs.