GE lp33 20 series Installation Manual

Critical PowerModifications reserved Page 22/43GE_UPS_ISG_LPS_3UL_20K_30K_2US_V010.docx Installation Guide LP33 Series 20 & 30 UL S24.7.2 Input/output over current protection and wire sizingThe cabling of the UPS system has to be sized according to the UPS power rating.Sizing of circuit breakers, fuses and cables for Input Utility, Output Load and Battery must meet therequirements of local and national electrical codes.Before connecting the UPS, verify that the Utility Voltage and Frequency, the Output Load Voltage andFrequency and Battery Data (cells number, floating voltage, autonomy) are according to the requiredspecifications.Output load configuration may be such that one phase may carry a load current at 100% of thatphase’s maximum current rating while the other two phases run at 0% or any combination in between.Ensure that the load does not consist of any equipment that may require high starting currents such aselectric motors, laser printers, etc.This may cause the UPS to occasionally go into Bypass due to overload conditionsTo choose the correct input fuses or circuit breaker, consider the available short-circuit current of thesystem up-stream.Choose the correct fuse or breaker using current data shown in the chart and the appropriate NECcode.The ratings indicated in the following chart do not consider any line voltage drop.In case of optional input transformer the input protective devices should be sized to allow thetransformer magnetization inrush current.Caution when using four-pole circuit breakers as protection.A potential problem exists for situations with non-linear loads:The neutral current could be greater than the phase currents.The three-phase Utility power supply must be symmetrical with respect to ground, due to the existenceof voltage surge protection devices inside the UPS.NOTE !If you use ELCB breaker (Earth Limiting Circuit Breaker) to protect the inputconnections, consider the high leakage current generated by the noise suppressioncapacitors.If these ELCB breakers are strictly necessary, we suggest using the largest typesuitable for non-linear current and for delayed operations.To ensure coordination when the UPS is configured for Separate Bypass and Rectifier Inputs, special caremust be taken in choosing the fuse or circuit breaker ratings installed in the output distribution circuits.Protective devices on the output of the UPS should be coordinated with the Bypass Input circuitprotection.Due to the relatively low short circuit capability of the UPS inverter, a short circuit in the load will causean immediate transfer to Bypass.The largest fuse or circuit breaker in the output distribution should be rated at no more than 60% of therating of the protective device supplying the Bypass line.If circuit selectivity is required while the load is fed from the inverter (Bypass Utility not available), thelargest fuse or circuit breaker should be rated at no more than 20% of the UPS output current rating.