however , most of the street lighting in Europe falls in protection class II .
For luminaires in protection class II , all the live parts have protective insulation but there is no defined connection to the protective earth . Surge protection devices ( surge arresters ) must not compromise the protective insulation in accordance with IEC61643-11 even for the very short timespans of a lightning strike . Optimum surge protection in the form of a conductor connected to the metal housing or to earth is not possible in a protection class II luminaire . In protection class II a distinction is made between designs featuring a luminaire head made of metal and ones in which the luminaire head is made from a non-conductive material .
With a luminaire head made of metal it is best to provide equipotential bonding between the control gear and the LED module , to prevent potential drag and increased overvoltages . Even if the luminaire head is connected to earth via the mast this connection may have a high or undefined impedance and the system should be provided with appropriate insulation in accordance with protection class II .
If the luminaire head is made of nonconductive material , all the exposed parts must also be made of non-conductive material or be insulated in accordance with protection class II . Equipotential bonding is not necessary here . The weakest link here is the LED module and it depends on the insulation material and its thickness as to whether surge protection of 10kV can be achieved . Without reliable surge protection the light sources may be subject to premature ageing and even complete failure .
Recommendations for reliable surge protection
According to the ZVEI , the Central Association for the German Electrical and Electronics Industry , the requirement for surge protection up to 10kV for luminaires in protection class II is being included in more and more tenders for street lighting projects . If there is an option of converting the lighting to protection class I this would be the best solution .
There are high quality drivers for LED luminaires such as the Premium Outdoor Drivers from Tridonic . These drivers have built-in surge protection against fluctuations in voltage that result from switching operations in the power supply system and occur between L and N . The drivers also offer surge protection up to 10kV between the power lines ( L and N ) and earth . This level of protection is
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tested to IEC61000-4-5 and will withstand even multiple overvoltage events . A special voltage splitting arrangement in the driver based on different capacitors ensure that even in the case of high input transients a maximum of only 500V reaches the output side of the driver . Most of the voltage decreases from the power side to the output side . For regions with only low to average frequency of lightning strikes control gear with 10kV offers high surge protection which previously could only be achieved with an additional surge module in the luminaire head . This is no longer permitted in protection class II luminaires however .
Lightning strikes that occur within a radius of 150m from an LED street light can no longer affect the reliable operation of the LED module . If lightning strikes a luminaire directly , and assuming a LED luminaire spacing of 30m , the first five would fail but not the luminaires in an entire street run .
For regions with a high incidence of lightning strikes a surge arrester in the main distributor for the lighting system is recommended in addition to the Tridonic drivers or , if the distributor is too far away , in the cable junction box . These external overvoltage devices must be tested in accordance with EN61643-11 and matched to the integrated surge protection in the luminaire , in other words in the control gear .
As high voltage tests on LED street lights in accordance with ÖVE / ÖNORM EN61547 at the certified AIT ( Austrian Institute of Technology ) have shown , compliance with the usual testing standards is not sufficient to guarantee the operational reliability of outdoor lighting installations . Actual practice shows that lamp failures occur even if the requirements of the standard are met , in some cases at overvoltages of only 2 to 4kV . In contrast to the standard tests , the tests carried out by the AIT involved increasing the voltage until the devices were destroyed . The results of the tests generally match the experiences from actual practice . Surge protection equipment only functions reliably if all the elements in the entire system are matched to one another . The higher the dielectric strength ( surge and ESD ) between L and N and also between L / N and earth ( PE ) the better the LED light sources will be able to withstand overvoltages during actual operation .
Protective earth is defined as earthing of one or more points in a system , installation or component for the purposes of electrical safety . This is generally understood to be the electrical connection of all the metal parts which are easily
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Overvoltages due to lightning strikes are much more difficult to calculate . |
accessible to touch and which do not belong to the operating current circuit ( ie . inactive metal parts ) to ground potential to prevent high contact voltages at the conductive components ( eg . the housing ) in the event of a fault .
In contrast to the protective earth , the functional earth or operational earth is provided not for the sake of safety or to protect people but to ensure trouble free operation of electrical installations . The functional earth can reliably protect against interference currents . The functional earth also provides common reference potentials between electrical devices .
Electrical devices in protection class I have a protective earth . Connecting the protective earth to the device housing ensures that in the event of a fault any fault current is routed to ground potential via the protective earth conductor . Equipment in protection class II has reinforced or double insulation between the mains circuit and the output voltage or metal casing . Even if the equipment has conductive surfaces they are protected by good insulation against contact with other live parts .
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