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ABB i-bus
KNX
Device technology
2.8
Ballast calculation
The electronic ballast is a device for operating gas discharge lamps, e.g. fluorescent lamps. During normal
operation, it converts the mains voltage to an optimum operating voltage for gas discharge lamps. It also
enables them to ignite (start) via capacitor circuitry.
With the original choke/starter circuitry the lamps switch on consecutively, with the electronic ballast all
fluorescent lamps switch on practically simultaneously. If switch-on occurs at the mains voltage peak, the
buffer capacitors of the electronic ballast cause a high but very short current pulse. When using several
ballasts on the same circuit, the simultaneous charging of the capacitors may result in very large system
inrush currents.
This peak inrush current I
selecting the respective circuit protection. The effects of the electronic ballast peak inrush current and the
associated limitation of the number of electronic ballasts on the SA/S are examined below.
The inrush current of the electronic ballast depends not only on the wattage but also on the type,
the number of elements (lamps) and on the manufacturer. For this reason, the given maximum number
of connectible electronic ballasts per output can only relate to a defined type of electronic ballast.
For a different ballast type, this value can only represent an estimation.
In order to properly estimate the number of electronic ballasts, the peak inrush current I
associated pulse width of the electronic ballast must be known. In the meantime, these values are stated
by manufacturers in the technical data or are available on request.
Typical values for single element electronic ballasts with T5/T8 lamps are:
Peak inrush current 15...50 A with a pulse time of 120...200 µs.
The Switch Actuator relays have the following maximum starting values:
(150 µs)
Max. peak inrush current I
p
(250 µs)
Max. peak inrush current I
p
(600 µs)
Max. peak inrush current I
p
*) x = 5 or 6, C-load types with and without load current detection
Caution
Do not exceed the threshold values.
Exceeding the value leads to destruction of the relay, e.g. due to welding.
42 2CDC 505 056 D0208 | SA/S
is to be considered when designing the switch contacts as well as when
p
SA/S 4.6.1.1
SA/S 2.6.2.1
SA/S 8.6.1.1
SA/S 4.6.2.1
SA/S 12.6.1.1
SA/S 8.6.2.1
SA/S 12.6.2.1
200 A
400 A
320 A
160 A
100 A
200 A
SA/S 2.10.2.1
SA/S 2.16.2.1
SA/S 4.10.2.1
SA/S 4.16.2.1
SA/S 8.10.2.1
SA/S 8.16.2.1
SA/S 12.10.2.1
SA/S 12.16.2.1
400 A
400 A
320 A
320 A
200 A
200 A
and the
p
SA/S 2.16.5.1
SA/S 2.16.6.1
SA/S 4.16.5.1
SA/S 4.16.6.1
SA/S 8.16.5.1
SA/S 8.16.6.1
SA/S 12.16.5.1
SA/S 12.16.6.1
600 A
600 A
480 A
480 A
300 A
300 A
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