1General Introduction Design and selection of equipment for low voltage electrical installations requires to consider and check the behavior of all devices on the current path in fault situation. High short-circuit current can damage equipment by electrodynamical and thermal effects. Each device can individually withstand the worst effects, but it may require significant oversizing and, on occasion, may be impossible. So the protection of each devices or equipment relies on upstream over-current protective device. In that case the proper “coordination” between the two devices shall be checked.Lower amplitude faults such as overloads or some earth faults can also create disturbances by causing trips and power interruptions for larger sections of the installation than expected.European Harmonization document HD60364-5-53 2015 for Low voltage electrical installation provides the following definition of coordination of electrical equipment: 530.3.5 Co-ordination of electrical equipment: correct way of selecting electrical devices in series to ensure safety and continuity of service of the installation taking into account short-circuit protection and/or overload protection and/or selectivitySchneider Electric provides "co-ordination" performances for two or three low voltage devices in the following cases: Coordination related to continuity of service bSelectivity (also called discrimination) bSelectivity enhanced by cascading bMotor starter coordination type 2 bCircuit-breaker and LV/LV transformersCoordination related to safety b Cascading (also called group short-circuit protection, or back up protection) bMotor starter coordination type 1 b Coordination between switch-disconnector and circuit breaker or fuses b Coordination between circuit breaker and busbar trunking (busway) systemFor coordination of Surge protection device with upstream overcurrent protection see our Design guide: https://download.schneider-electric.com/files?p_Doc_Ref=CA903014E
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