Selective Coordination - Cooper Bussmann

Selective CoordinationFusesFor the next example, the Selectivity Ratio Guide suggests that the minimumratio between line side and load side fuse should be at least 2:1. The one-lineshows Low-Peak ® fuses KRP-C-1000SP feeding a LPS-RK-200SP. The ratioof amp ratings is 5:1 (1000:200) which indicates coordination between thesefuses. Continuing further into the system the LPS-RK-200SP feeds aLPJ-60SP. This ratio of amp ratings is 3.33:1 (200:60), which also indicatesa selectively coordinated system.I pAvailableShort-Circuit Current480/277VI 1 pKRP-C-1000SPAmp FuseLet Through EnergyLine SideLoad SideLow-PeakTime-Delay FuseKRP-C-1000SPt mt ct aLow-PeakLPS-RK-200SPDual-Element FuseLPS-RK-200SPAmp FuseLet Through EnergyLine SideLoad Sidet mt ct cLow-PeakLPJ-60SPDual-Element FuseFaultLPJ-60SPAmp FuseLet Through Energy*Requirements for selectivity—Total clearing energy of load side fuse is less than melting energy of line side fuse.*Area under the curves is not actual energy but is indicative of let-through energy. Actual let-through energy is I 2 rt.92 ©2005 Cooper Bussmann