PlantFlow 3D › Guides › Lighting control with a photocell and a HAND–0–AUTO switch
Lighting control with a photocell and a HAND–0–AUTO switch
How outdoor and street lighting is switched automatically by a photocell through a lighting contactor, with a selector for maintenance.
The circuit
Outdoor floodlights and street lights are usually switched by a lighting contactor rather than directly by a switch, because the total current is high and the control should come from several places. A small control circuit energises the contactor coil, and its main contacts switch the line and neutral of the lighting circuit.
The photocell
A photocell measures the daylight. When the light falls below its switch-on level it closes its output contact; when the light rises above a higher switch-off level it opens again. The difference between the two levels (hysteresis) and a short delay stop clouds, shadows or car headlights from switching the lights on and off repeatedly.
The photocell needs its own supply on terminals such as A1 and A2. If that supply is missing the contact never closes.
HAND–0–AUTO
A selector switch gives three choices. HAND switches the lights on regardless of the daylight, which is useful for maintenance and testing. 0 keeps them off. AUTO passes control to the photocell. The panel often has a pilot lamp that shows when the contactor is energised.
Safety and selection
The switch or contact must always break the line conductor; a switch in the neutral leaves the lamp holders live. LED drivers draw a high inrush current when they switch on, so choose the contactor and the circuit breaker from the manufacturer’s lamp-load tables, not only from the normal current. Earth the metal bodies of the luminaires.
Try it yourself
Choose “Lighting control” in the simulator. In AUTO press the day/night button and watch the photocell switch the floodlights after its delay, then try HAND and 0.
Open the PlantFlow 3D simulator →Safety: this guide explains principles for learning. Real installations must follow the applicable codes, the equipment manufacturer's instructions and the approval of a competent, qualified person. Isolate, lock off and prove dead before touching any circuit.