Lighting, socket circuits 19.02.2020 17:35 19.02.2020 17:35

Electronic ballasts, whether they are controlled by a 0 to 10 V signal or by a DALI or DSI interface, have very often a significant capacitive load, and at the moment of switching the supply voltage, they draw for a short period multiple times higher current.



  • some OSRAM ballasts draw up to 10 times higher current than the standard rated current,

  • the Helvar ballast EL1/2x18-42TCS can take during the first 192 μs (the so-called cold start) the current up to 40 A.


These maximum current values also dependent on the length and cross section of the wires.

When several ballasts are being switched simultaneously, what must be taken into account is both the maximum through the switching relay contact, and also upstream fusing (to avoid the release of the upstream circuit breaker).


The Tridonic ballast PCA 1x14 T5 BASIC Ip x! Tec II draws up to 19.6 A for 147 μs, with the 2.5 mm2 cross-section of the supply cable (yet the rated ballast current is only 0.08A!). The manufacturer provides a tabular chart with the maximum number of ballasts that can be connected simultaneously without tripping the circuit breaker; this is listed for each specific type of ballast, the cable cross-section and the front-end circuit breaker (characteristics and rated current).


Therefore, it is always necessary - when choosing a suitable connection (the type of relays, the number of simultaneously switching ballasts) - to take into account the parameters provided by the manufacturer.


We recommend using a relay contact with minimum switching current of 80 A for switching a single ballast, such as the C-OR-0008M or C-LC-0202B (it can be stated that a relay with inrush switching current below 40 A is of very little use for switching ballasts); when switching several ballasts simultaneously it is necessary to use a relay with a higher switching current: we recommend using modules fitted with relays with switching current of 800 A - e.g. the C-OR-0011M.

If there are more than 4 simultaneously switching ballasts, it is necessary to thoroughly examine the maximum switching currents of the ballasts and the type of circuit breaker used in order to make sure that the front-end protection is reliable; sometimes it is necessary to divide the ballasts on several relay contacts and the SW should handle the consecutive switching (in large premises, such as industrial halls, etc., this method of control is acceptable).