IEC 62109-1 is the general part of the safety standard for power converters used in photovoltaic power systems. It applies to the inverters, d.c. to d.c. converters and charge controllers that form part of a photovoltaic installation, from small module-level converters to the central inverters of utility scale plants. Photovoltaic converters present a particular safety problem because their source cannot be switched off: the array continues to generate while illuminated, so the input circuit remains live even when the converter is disconnected, and this must be accounted for in the design of the equipment and in the instructions supplied with it. The standard defines the protection against electric shock through insulation, clearances and creepage distances, the requirements for the enclosure and for protection against access to live parts, and the measures against fire, energy and thermal hazards. It specifies the tests for dielectric strength, insulation resistance, limited power source verification, temperature rise and abnormal operation, and it includes requirements for the safety of the control circuits and for the marking of the product.