Power Supply - Siemens FDA241 Technical Manual

4.3
Building Technologies
Fire Safety

Power supply

The normal status and the alarm status must be taken into account when
dimensioning the power supply. When the normal status applies, the power supply
must provide the quiescent current for the smoke aspiration systems and ensure
that the emergency batteries are charged in accordance with VDE 0883, Part 1.
When the alarm status applies, additional power is required. Take this into account
when dimensioning the batteries. The batteries must be designed to support a
bridging time of 24 hours in the normal status and 1 hour in the alarm status.
You will find details of the aspirating smoke detector's current consumption in
chapter 'Technical data for FDA241, FDA221 [➙ 105]'.
Line calculation
The maximum length of the line is calculated on the basis of the permissible
voltage drop on the supply line. The permissible voltage drop is the difference
between the final voltage of the batteries (21.5 V) and the lower operating voltage
limit of the smoke aspiration systems.
L
= Maximum length of line in [m]
max
∆U = Max. voltage drop on supply line
A
= Wire cross-section in [mm²]
I
= Maximum current of all aspirating smoke detectors in alarm status in [A]
alarm
Ƴ = Specific resistance: Cu = 0.0175 Ω mm²/m
To ensure the housing remains properly sealed, select the relevant grommet for
the cable concerned.
M20 cable grommet: Ø 8...12 mm

M25 cable grommet: Ø 9...14 mm

Also observe the notices in the 'Technical data for FDA241, FDA221 [➙ 105]'
chapter.
Capacity calculation
Use the following formula to calculate the nominal capacity of the batteries:
K = Nominal capacity of emergency battery in [Ah]
nominal
I
= Quiescent current [A]
quiescent
I
= Maximum current of all aspirating smoke detectors in alarm status in [A]
alarm
n
= Number of aspirating smoke detectors
t
= Required bridging time during operation in [h] (typically 24 h)
1
t
= Required bridging time in the case of an alarm in [h] (typically 1 h)
2
1.25 = The factor of 1.25 ceases to apply with bridging times of more than 24 hours.
See also
 External power unit and batteries [➙ 31]
Planning
4
Power supply
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2015-09-29