The HF-ballast senses the voltage in the control circuit. The lower the voltage, the lower the lighting level. If the control circuit is left open, the luminaire lights at full strength in the same way as an non-controlled luminaire operates. If the circuit is closed the lighting level drops to the minimum value. The minimum level of luminous flux varies depending on the manufacturer, type and light source. Normal minimum levels for linear fluorescent lamps are 1–5 %, and 3–10 % for compact fluorescent lamps. Check which levels apply for the luminaire you are interested in.
Apart from the phase, neutral and protective conductors, two other control circuit wires are connected to the luminaire. The control wires can be placed in the same conduit as the mains voltage cable feeding the luminaire. Even if the control voltage is a maximum of 10 V the insulation on the control wires must conform to the demands for a heavy current installation. You must ensure the polarity is correct when connecting the control circuit as incorrect connection can mean the installation drops to its minimum state.
In addition to the control wires, the phase conductor should also be connected via the control unit or combined potentiometer/mains switch, as the luminaires can only be switched on and off via the mains voltage. It is important to remember this when planning the cabling, as changes to the installation may be difficult at a later stage.
The breaking capacity of the potentiometer’s switch should be taken into consideration during installation. Even if the potentiometer is capable of regulating up to 50 HF-ballasts, the capacity of the switch is usually 5–10 luminaires depending on their load. Contactors are needed for greater loads.
- When selecting the control system you should take the system’s and luminaire’s compatibility into consideration. Luminaires designed according to the standard EN 60929 feed the control circuits themselves, which not all analogue control units permit.
- There are special demands for running control cables in enclosures together with other high current cables.
- The polarity of the control circuit must be maintained throughout. Regulation does not work correctly if the polarity is crossed on any of the luminaires in a group.